qgsvectorlayer.h

/***************************************************************************
                          qgsvectorlayer.h  -  description
                             -------------------
    begin                : Oct 29, 2003
    copyright            : (C) 2003 by Gary E.Sherman
    email                : sherman at mrcc.com
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/

#ifndef QGSVECTORLAYER_H
#define QGSVECTORLAYER_H

#include <QMap>
#include <QSet>
#include <QList>
#include <QStringList>
#include <QFont>
#include <QMutex>

#include "qgis.h"
#include "qgsmaplayer.h"
#include "qgsfeature.h"
#include "qgsfeaturerequest.h"
#include "qgseditorwidgetconfig.h"
#include "qgsfields.h"
#include "qgssnapper.h"
#include "qgsvectorsimplifymethod.h"
#include "qgseditformconfig.h"
#include "qgsattributetableconfig.h"
#include "qgsaggregatecalculator.h"
#include "qgsfeatureiterator.h"
#include "qgsexpressioncontextgenerator.h"

class QPainter;
class QImage;

class QgsAbstractGeometrySimplifier;
class QgsActionManager;
class QgsConditionalLayerStyles;
class QgsCoordinateTransform;
class QgsCurve;
class QgsDiagramLayerSettings;
class QgsDiagramRenderer;
class QgsEditorWidgetWrapper;
class QgsExpressionFieldBuffer;
class QgsFeatureRenderer;
class QgsGeometry;
class QgsGeometryCache;
class QgsGeometryVertexIndex;
class QgsMapToPixel;
class QgsRectangle;
class QgsRectangle;
class QgsRelation;
class QgsRelationManager;
class QgsSingleSymbolRenderer;
class QgsSymbol;
class QgsVectorDataProvider;
class QgsVectorLayerEditBuffer;
class QgsVectorLayerJoinBuffer;
class QgsAbstractVectorLayerLabeling;
class QgsPointV2;

typedef QList<int> QgsAttributeList;
typedef QSet<int> QgsAttributeIds;
typedef QList<QgsPointV2> QgsPointSequence;


struct CORE_EXPORT QgsVectorJoinInfo
{
  QgsVectorJoinInfo()
      : memoryCache( false )
      , cacheDirty( true )
      , targetFieldIndex( -1 )
      , joinFieldIndex( -1 )
  {}

  //! Join field in the target layer
  QString targetFieldName;
  //! Source layer
  QString joinLayerId;
  //! Join field in the source layer
  QString joinFieldName;
  //! True if the join is cached in virtual memory
  bool memoryCache;
  //! True if the cached join attributes need to be updated
  bool cacheDirty;

  /** Cache for joined attributes to provide fast lookup (size is 0 if no memory caching)
   * @note not available in python bindings
   */
  QHash< QString, QgsAttributes> cachedAttributes;

  //! Join field index in the target layer. For backward compatibility with 1.x (x>=7)
  int targetFieldIndex;
  //! Join field index in the source layer. For backward compatibility with 1.x (x>=7)
  int joinFieldIndex;

  /** An optional prefix. If it is a Null string "{layername}_" will be used
   * @note Added in 2.8
   */
  QString prefix;

  bool operator==( const QgsVectorJoinInfo& other ) const
  {
    return targetFieldName == other.targetFieldName &&
           joinLayerId == other.joinLayerId &&
           joinFieldName == other.joinFieldName &&
           joinFieldsSubset == other.joinFieldsSubset &&
           memoryCache == other.memoryCache &&
           prefix == other.prefix;
  }

  /** Set subset of fields to be used from joined layer. Takes ownership of the passed pointer. Null pointer tells to use all fields.
    @note added in 2.6 */
  void setJoinFieldNamesSubset( QStringList* fieldNamesSubset ) { joinFieldsSubset = QSharedPointer<QStringList>( fieldNamesSubset ); }
  /** Get subset of fields to be used from joined layer. All fields will be used if null is returned.
    @note added in 2.6 */
  QStringList* joinFieldNamesSubset() const { return joinFieldsSubset.data(); }

protected:
  //! Subset of fields to use from joined layer. null = use all fields
  QSharedPointer<QStringList> joinFieldsSubset;
};



/** \ingroup core
 * Represents a vector layer which manages a vector based data sets.
 *
 * The QgsVectorLayer is instantiated by specifying the name of a data provider,
 * such as postgres or wfs, and url defining the specific data set to connect to.
 * The vector layer constructor in turn instantiates a QgsVectorDataProvider subclass
 * corresponding to the provider type, and passes it the url.  The data provider
 * connects to the data source.
 *
 * The QgsVectorLayer provides a common interface to the different data types.  It also
 * manages editing transactions.
 *
 *  Sample usage of the QgsVectorLayer class:
 *
 * \code
 *     QString uri = "point?crs=epsg:4326&field=id:integer";
 *     QgsVectorLayer *scratchLayer = new QgsVectorLayer(uri, "Scratch point layer",  "memory");
 * \endcode
 *
 * The main data providers supported by QGIS are listed below.
 *
 * \section providers Vector data providers
 *
 * \subsection memory Memory data providerType (memory)
 *
 * The memory data provider is used to construct in memory data, for example scratch
 * data or data generated from spatial operations such as contouring.  There is no
 * inherent persistent storage of the data.  The data source uri is constructed.  The
 * url specifies the geometry type ("point", "linestring", "polygon",
 * "multipoint","multilinestring","multipolygon"), optionally followed by url parameters
 * as follows:
 *
 * - crs=definition
 *   Defines the coordinate reference system to use for the layer.
 *   definition is any string accepted by QgsCoordinateReferenceSystem::createFromString()
 *
 * - index=yes
 *   Specifies that the layer will be constructed with a spatial index
 *
 * - field=name:type(length,precision)
 *   Defines an attribute of the layer.  Multiple field parameters can be added
 *   to the data provider definition.  type is one of "integer", "double", "string".
 *
 * An example url is "Point?crs=epsg:4326&field=id:integer&field=name:string(20)&index=yes"
 *
 * \subsection ogr OGR data provider (ogr)
 *
 * Accesses data using the OGR drivers (http://www.gdal.org/ogr/ogr_formats.html). The url
 * is the OGR connection string.  A wide variety of data formats can be accessed using this
 * driver, including file based formats used by many GIS systems, database formats, and
 * web services.  Some of these formats are also supported by custom data providers listed
 * below.
 *
 * \subsection spatialite Spatialite data provider (spatialite)
 *
 * Access data in a spatialite database. The url defines the connection parameters, table,
 * geometry column, and other attributes.  The url can be constructed using the
 * QgsDataSourceUri class.
 *
 * \subsection postgres Postgresql data provider (postgres)
 *
 * Connects to a postgresql database.  The url defines the connection parameters, table,
 * geometry column, and other attributes.  The url can be constructed using the
 * QgsDataSourceUri class.
 *
 * \subsection mssql Microsoft SQL server data provider (mssql)
 *
 * Connects to a Microsoft SQL server database.  The url defines the connection parameters, table,
 * geometry column, and other attributes.  The url can be constructed using the
 * QgsDataSourceUri class.
 *
 * \subsection wfs WFS (web feature service) data provider (wfs)
 *
 * Used to access data provided by a web feature service.
 *
 * The url can be a HTTP url to a WFS server (legacy, e.g. http://foobar/wfs?TYPENAME=xxx&SRSNAME=yyy[&FILTER=zzz]), or,
 * starting with QGIS 2.16, a URI constructed using the QgsDataSourceUri class with the following parameters :
 * - url=string (mandatory): HTTP url to a WFS server endpoint. e.g http://foobar/wfs
 * - typename=string (mandatory): WFS typename
 * - srsname=string (recommended): SRS like 'EPSG:XXXX'
 * - username=string
 * - password=string
 * - authcfg=string
 * - version=auto/1.0.0/1.1.0/2.0.0
 *  -sql=string: full SELECT SQL statement with optional WHERE, ORDER BY and possibly with JOIN if supported on server
 * - filter=string: QGIS expression or OGC/FES filter
 * - restrictToRequestBBOX=1: to download only features in the view extent (or more generally
 *   in the bounding box of the feature iterator)
 * - maxNumFeatures=number
 * - IgnoreAxisOrientation=1: to ignore EPSG axis order for WFS 1.1 or 2.0
 * - InvertAxisOrientation=1: to invert axis order
 * - hideDownloadProgressDialog=1: to hide the download progress dialog
 *
 * The ‘FILTER’ query string parameter can be used to filter
 * the WFS feature type. The ‘FILTER’ key value can either be a QGIS expression
 * or an OGC XML filter. If the value is set to a QGIS expression the driver will
 * turn it into OGC XML filter before passing it to the WFS server. Beware the
 * QGIS expression filter only supports” =, !=, <, >, <=, >=, AND, OR, NOT, LIKE, IS NULL”
 * attribute operators, “BBOX, Disjoint, Intersects, Touches, Crosses, Contains, Overlaps, Within”
 * spatial binary operators and the QGIS local “geomFromWKT, geomFromGML”
 * geometry constructor functions.
 *
 * Also note:
 *
 * - You can use various functions available in the QGIS Expression list,
 *   however the function must exist server side and have the same name and arguments to work.
 *
 * - Use the special $geometry parameter to provide the layer geometry column as input
 *   into the spatial binary operators e.g intersects($geometry, geomFromWKT('POINT (5 6)'))
 *
 * \subsection delimitedtext Delimited text file data provider (delimitedtext)
 *
 * Accesses data in a delimited text file, for example CSV files generated by
 * spreadsheets. The contents of the file are split into columns based on specified
 * delimiter characters.  Each record may be represented spatially either by an
 * X and Y coordinate column, or by a WKT (well known text) formatted columns.
 *
 * The url defines the filename, the formatting options (how the
 * text in the file is divided into data fields, and which fields contain the
 * X,Y coordinates or WKT text definition.  The options are specified as url query
 * items.
 *
 * At its simplest the url can just be the filename, in which case it will be loaded
 * as a CSV formatted file.
 *
 * The url may include the following items:
 *
 * - encoding=UTF-8
 *
 *   Defines the character encoding in the file.  The default is UTF-8.  To use
 *   the default encoding for the operating system use "System".
 *
 * - type=(csv|regexp|whitespace|plain)
 *
 *   Defines the algorithm used to split records into columns. Records are
 *   defined by new lines, except for csv format files for which quoted fields
 *   may span multiple records.  The default type is csv.
 *
 *   -  "csv" splits the file based on three sets of characters:
 *      delimiter characters, quote characters,
 *      and escape characters.  Delimiter characters mark the end
 *      of a field. Quote characters enclose a field which can contain
 *      delimiter characters, and newlines.  Escape characters cause the
 *      following character to be treated literally (including delimiter,
 *      quote, and newline characters).  Escape and quote characters must
 *      be different from delimiter characters. Escape characters that are
 *      also quote characters are treated specially - they can only
 *      escape themselves within quotes.  Elsewhere they are treated as
 *      quote characters.  The defaults for delimiter, quote, and escape
 *      are ',', '"', '"'.
 *   -  "regexp" splits each record using a regular expression (see QRegExp
 *      documentation for details).
 *   -  "whitespace" splits each record based on whitespace (on or more whitespace
 *      characters.  Leading whitespace in the record is ignored.
 *   -  "plain" is provided for backwards compatibility.  It is equivalent to
 *      CSV except that the default quote characters are single and double quotes,
 *      and there is no escape characters.
 *
 * - delimiter=characters
 *
 *   Defines the delimiter characters used for csv and plain type files, or the
 *   regular expression for regexp type files.  It is a literal string of characters
 *   except that "\t" may be used to represent a tab character.
 *
 * - quote=characters
 *
 *   Defines the characters that are used as quote characters for csv and plain type
 *   files.
 *
 * - escape=characters
 *
 *   Defines the characters used to escape delimiter, quote, and newline characters.
 *
 * - skipLines=n
 *
 *   Defines the number of lines to ignore at the beginning of the file (default 0)
 *
 * - useHeader=(yes|no)
 *
 *   Defines whether the first record in the file (after skipped lines) contains
 *   column names (default yes)
 *
 * - trimFields=(yes|no)
 *
 *   If yes then leading and trailing whitespace will be removed from fields
 *
 * - skipEmptyFields=(yes|no)
 *
 *   If yes then empty fields will be discarded (eqivalent to concatenating consecutive
 *   delimiters)
 *
 * - maxFields=#
 *
 *   Specifies the maximum number of fields to load for each record.  Additional
 *   fields will be discarded.  Default is 0 - load all fields.
 *
 * - decimalPoint=c
 *
 *   Defines a character that is used as a decimal point in the numeric columns
 *   The default is '.'.
 *
 * - xField=column yField=column
 *
 *   Defines the name of the columns holding the x and y coordinates for XY point geometries.
 *   If the useHeader is no (ie there are no column names), then this is the column
 *   number (with the first column as 1).
 *
 * - xyDms=(yes|no)
 *
 *   If yes then the X and Y coordinates are interpreted as
 *   degrees/minutes/seconds format (fairly permissively),
 *   or degree/minutes format.
 *
 * - wktField=column
 *
 *   Defines the name of the columns holding the WKT geometry definition for WKT geometries.
 *   If the useHeader is no (ie there are no column names), then this is the column
 *   number (with the first column as 1).
 *
 * - geomType=(point|line|polygon|none)
 *
 *   Defines the geometry type for WKT type geometries.  QGIS will only display one
 *   type of geometry for the layer - any others will be ignored when the file is
 *   loaded.  By default the provider uses the type of the first geometry in the file.
 *   Use geomType to override this type.
 *
 *   geomType can also be set to none, in which case the layer is loaded without
 *   geometries.
 *
 * - subset=expression
 *
 *   Defines an expression that will identify a subset of records to display
 *
 * - crs=crsstring
 *
 *   Defines the coordinate reference system used for the layer.  This can be
 *   any string accepted by QgsCoordinateReferenceSystem::createFromString()
 *
 * -subsetIndex=(yes|no)
 *
 *   Determines whether the provider generates an index to improve the efficiency
 *   of subsets.  The default is yes
 *
 * -spatialIndex=(yes|no)
 *
 *   Determines whether the provider generates a spatial index.  The default is no.
 *
 * -watchFile=(yes|no)
 *
 *   Defines whether the file will be monitored for changes. The default is
 *   to monitor for changes.
 *
 * - quiet
 *
 *   Errors encountered loading the file will not be reported in a user dialog if
 *   quiet is included (They will still be shown in the output log).
 *
 * \subsection gpx GPX data provider (gpx)
 *
 * Provider reads tracks, routes, and waypoints from a GPX file.  The url
 * defines the name of the file, and the type of data to retrieve from it
 * ("track", "route", or "waypoint").
 *
 * An example url is "/home/user/data/holiday.gpx?type=route"
 *
 * \subsection grass Grass data provider (grass)
 *
 * Provider to display vector data in a GRASS GIS layer.
 *
 * TODO QGIS3: Remove virtual from non-inherited methods (like isModified)
 */


class CORE_EXPORT QgsVectorLayer : public QgsMapLayer, public QgsExpressionContextGenerator
{
    Q_OBJECT

    Q_PROPERTY( QString displayExpression READ displayExpression WRITE setDisplayExpression NOTIFY displayExpressionChanged )
    Q_PROPERTY( QString mapTipTemplate READ mapTipTemplate WRITE setMapTipTemplate NOTIFY mapTipTemplateChanged )
    Q_PROPERTY( QgsEditFormConfig editFormConfig READ editFormConfig WRITE setEditFormConfig NOTIFY editFormConfigChanged )
    Q_PROPERTY( bool readOnly READ isReadOnly WRITE setReadOnly NOTIFY readOnlyChanged )

  public:

    //! Result of an edit operation
    enum EditResult
    {
      Success = 0, //!< Edit operation was successful
      EmptyGeometry = 1, //!< Edit operation resulted in an empty geometry
      EditFailed = 2, //!< Edit operation failed
      FetchFeatureFailed = 3, //!< Unable to fetch requested feature
      InvalidLayer = 4, //!< Edit failed due to invalid layer
    };

    //! Selection behaviour
    enum SelectBehaviour
    {
      SetSelection, //!< Set selection, removing any existing selection
      AddToSelection, //!< Add selection to current selection
      IntersectSelection, //!< Modify current selection to include only select features which match
      RemoveFromSelection, //!< Remove from current selection
    };

    /** Constructor - creates a vector layer
     *
     * The QgsVectorLayer is constructed by instantiating a data provider.  The provider
     * interprets the supplied path (url) of the data source to connect to and access the
     * data.
     *
     * @param  path  The path or url of the parameter.  Typically this encodes
     *               parameters used by the data provider as url query items.
     * @param  baseName The name used to represent the layer in the legend
     * @param  providerLib  The name of the data provider, eg "memory", "postgres"
     * @param  loadDefaultStyleFlag whether to load the default style
     *
     */
    QgsVectorLayer( const QString& path = QString::null, const QString& baseName = QString::null,
                    const QString& providerLib = QString::null, bool loadDefaultStyleFlag = true );

    //! Destructor
    virtual ~QgsVectorLayer();

    //! Returns the permanent storage type for this layer as a friendly name.
    QString storageType() const;

    //! Capabilities for this layer in a friendly format.
    QString capabilitiesString() const;

    //! Returns a comment for the data in the layer
    QString dataComment() const;

    /**
     * This is a shorthand for accessing the displayExpression if it is a simple field.
     * If the displayExpression is more complex than a simple field, a null string will
     * be returned.
     *
     * @see displayExpression
     */
    QString displayField() const;

    /** Set the preview expression, used to create a human readable preview string.
     *  Used e.g. in the attribute table feature list. Uses { @link QgsExpression }.
     *
     *  @param displayExpression The expression which will be used to preview features
     *                           for this layer
     */
    void setDisplayExpression( const QString& displayExpression );

    /**
     *  Get the preview expression, used to create a human readable preview string.
     *  Uses { @link QgsExpression }
     *
     *  @return The expression which will be used to preview features for this layer
     */
    QString displayExpression() const;

    //! Returns the data provider
    QgsVectorDataProvider* dataProvider();

    /** Returns the data provider in a const-correct manner
     * @note not available in python bindings
     */
    const QgsVectorDataProvider* dataProvider() const;

    //! Sets the textencoding of the data provider
    void setProviderEncoding( const QString& encoding );

    //! Setup the coordinate system transformation for the layer
    void setCoordinateSystem();

    /** Joins another vector layer to this layer
      @param joinInfo join object containing join layer id, target and source field
      @note since 2.6 returns bool indicating whether the join can be added */
    bool addJoin( const QgsVectorJoinInfo& joinInfo );

    /** Removes a vector layer join
      @returns true if join was found and successfully removed */
    bool removeJoin( const QString& joinLayerId );

    /**
     * Acccessor to the join buffer object
     * @note added 2.14.7
     */
    QgsVectorLayerJoinBuffer* joinBuffer() { return mJoinBuffer; }
    const QList<QgsVectorJoinInfo> vectorJoins() const;

    /**
     * Sets the list of dependencies.
     * @see dependencies()
     *
     * @param layers set of QgsMapLayerDependency. Only user-defined dependencies will be added
     * @returns false if a dependency cycle has been detected
     * @note added in QGIS 3.0
     */
    virtual bool setDependencies( const QSet<QgsMapLayerDependency>& layers ) override;

    /**
     * Gets the list of dependencies. This includes data dependencies set by the user (@see setDataDependencies)
     * as well as dependencies given by the provider
     *
     * @returns a set of QgsMapLayerDependency
     * @note added in QGIS 3.0
     */
    virtual QSet<QgsMapLayerDependency> dependencies() const override;

    /**
     * Add a new field which is calculated by the expression specified
     *
     * @param exp The expression which calculates the field
     * @param fld The field to calculate
     *
     * @return The index of the new field
     *
     * @note added in 2.6, return value added in 2.9
     */
    int addExpressionField( const QString& exp, const QgsField& fld );

    /**
     * Remove an expression field
     *
     * @param index The index of the field
     *
     * @note added in 2.6
     */
    void removeExpressionField( int index );

    /**
     * Returns the expression used for a given expression field
     *
     * @param index An index of an epxression based (virtual) field
     *
     * @return The expression for the field at index
     *
     * @note added in 2.9
     */
    QString expressionField( int index ) const;

    /**
     * Changes the expression used to define an expression based (virtual) field
     *
     * @param index The index of the expression to change
     *
     * @param exp The new expression to set
     *
     * @note added in 2.9
     */
    void updateExpressionField( int index, const QString& exp );

    /**
     * Get all layer actions defined on this layer.
     *
     * The pointer which is returned directly points to the actions object
     * which is used by the layer, so any changes are immediately applied.
     */
    QgsActionManager* actions() { return mActions; }

    /**
     * The number of features that are selected in this layer
     *
     * @return See description
     */
    int selectedFeatureCount() const;

    /**
     * Select features found within the search rectangle (in layer's coordinates)
     * @param rect search rectangle
     * @param behaviour selection type, allows adding to current selection, removing
     * from selection, etc.
     * @see invertSelectionInRectangle(QgsRectangle & rect)
     * @see selectByExpression()
     * @see selectByIds()
     */
    void selectByRect( QgsRectangle & rect, SelectBehaviour behaviour = SetSelection );

    /** Select matching features using an expression.
     * @param expression expression to evaluate to select features
     * @param behaviour selection type, allows adding to current selection, removing
     * from selection, etc.
     * @note added in QGIS 2.16
     * @see selectByRect()
     * @see selectByIds()
     */
    void selectByExpression( const QString& expression, SelectBehaviour behaviour = SetSelection );

    /** Select matching features using a list of feature IDs. Will emit the
     * selectionChanged() signal with the clearAndSelect flag set.
     * @param ids feature IDs to select
     * @param behaviour selection type, allows adding to current selection, removing
     * from selection, etc.
     * @note added in QGIS 2.16
     * @see selectByRect()
     * @see selectByExpression()
     */
    void selectByIds( const QgsFeatureIds &ids, SelectBehaviour behaviour = SetSelection );

    /**
     * Modifies the current selection on this layer
     *
     * @param selectIds    Select these ids
     * @param deselectIds  Deselect these ids
     *
     * @see   select(QgsFeatureIds)
     * @see   select(QgsFeatureId)
     * @see   deselect(QgsFeatureIds)
     * @see   deselect(QgsFeatureId)
     * @see selectByExpression()
     */
    void modifySelection( const QgsFeatureIds& selectIds, const QgsFeatureIds &deselectIds );

    //! Select not selected features and deselect selected ones
    void invertSelection();

    //! Select all the features
    void selectAll();

    //! Get all feature Ids
    QgsFeatureIds allFeatureIds() const;

    /**
     * Invert selection of features found within the search rectangle (in layer's coordinates)
     *
     * @param rect  The rectangle in which the selection of features will be inverted
     *
     * @see   invertSelection()
     */
    void invertSelectionInRectangle( QgsRectangle & rect );

    /**
     * Get a copy of the user-selected features
     *
     * @return A list of { @link QgsFeature } 's
     *
     * @see    selectedFeaturesIds()
     * @see    selectedFeaturesIterator() which is more memory friendly when handling large selections
     */
    QgsFeatureList selectedFeatures() const;

    /**
     * Get an iterator of the selected features
     *
     * @param request You may specify a request, e.g. to limit the set of requested attributes.
     *                Any filter on the request will be discarded.
     *
     * @return Iterator over the selected features
     *
     * @see    selectedFeaturesIds()
     * @see    selectedFeatures()
     */
    QgsFeatureIterator selectedFeaturesIterator( QgsFeatureRequest request = QgsFeatureRequest() ) const;

    /**
     * Return reference to identifiers of selected features
     *
     * @return A list of { @link QgsFeatureId } 's
     * @see selectedFeatures()
     */
    const QgsFeatureIds &selectedFeaturesIds() const;

    //! Returns the bounding box of the selected features. If there is no selection, QgsRectangle(0,0,0,0) is returned
    QgsRectangle boundingBoxOfSelected() const;

    /** Returns whether the layer contains labels which are enabled and should be drawn.
     * @return true if layer contains enabled labels
     * @note added in QGIS 2.9
     */
    bool labelsEnabled() const;

    /** Returns whether the layer contains diagrams which are enabled and should be drawn.
     * @return true if layer contains enabled diagrams
     * @note added in QGIS 2.9
     */
    bool diagramsEnabled() const;

    //! Sets diagram rendering object (takes ownership)
    void setDiagramRenderer( QgsDiagramRenderer* r );
    const QgsDiagramRenderer* diagramRenderer() const { return mDiagramRenderer; }

    void setDiagramLayerSettings( const QgsDiagramLayerSettings& s );
    const QgsDiagramLayerSettings *diagramLayerSettings() const { return mDiagramLayerSettings; }

    //! Return renderer.
    QgsFeatureRenderer* renderer() { return mRenderer; }

    /** Return const renderer.
     * @note not available in python bindings
     */
    const QgsFeatureRenderer* renderer() const { return mRenderer; }

    /**
     * Set renderer which will be invoked to represent this layer.
     * Ownership is transferred.
     */
    void setRenderer( QgsFeatureRenderer* r );

    //! Returns point, line or polygon
    QgsWkbTypes::GeometryType geometryType() const;

    //! Returns true if this is a geometry layer and false in case of NoGeometry (table only) or UnknownGeometry
    bool hasGeometryType() const;

    //! Returns the WKBType or WKBUnknown in case of error
    QgsWkbTypes::Type wkbType() const;

    //! Return the provider type for this layer
    QString providerType() const;

    /** Reads vector layer specific state from project file Dom node.
     * @note Called by QgsMapLayer::readXml().
     */
    virtual bool readXml( const QDomNode& layer_node ) override;

    /** Write vector layer specific state to project file Dom node.
     * @note Called by QgsMapLayer::writeXml().
     */
    virtual bool writeXml( QDomNode & layer_node, QDomDocument & doc ) const override;

    /**
     * Save named and sld style of the layer to the style table in the db.
     * @param name
     * @param description
     * @param useAsDefault
     * @param uiFileContent
     * @param msgError
     */
    virtual void saveStyleToDatabase( const QString& name, const QString& description,
                                      bool useAsDefault, const QString& uiFileContent,
                                      QString &msgError );

    /**
     * Lists all the style in db split into related to the layer and not related to
     * @param ids the list in which will be stored the style db ids
     * @param names the list in which will be stored the style names
     * @param descriptions the list in which will be stored the style descriptions
     * @param msgError
     * @return the number of styles related to current layer
     */
    virtual int listStylesInDatabase( QStringList &ids, QStringList &names,
                                      QStringList &descriptions, QString &msgError );

    /**
     * Will return the named style corresponding to style id provided
     */
    virtual QString getStyleFromDatabase( const QString& styleId, QString &msgError );

    /**
     * Load a named style from file/local db/datasource db
     * @param theURI the URI of the style or the URI of the layer
     * @param theResultFlag will be set to true if a named style is correctly loaded
     * @param loadFromLocalDb if true forces to load from local db instead of datasource one
     */
    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag, bool loadFromLocalDb );

    /**
     * Calls loadNamedStyle( theURI, theResultFlag, false );
     * Retained for backward compatibility
     */
    virtual QString loadNamedStyle( const QString &theURI, bool &theResultFlag ) override;

    /** Read the symbology for the current layer from the Dom node supplied.
     * @param node node that will contain the symbology definition for this layer.
     * @param errorMessage reference to string that will be updated with any error messages
     * @return true in case of success.
     */
    bool readSymbology( const QDomNode& node, QString& errorMessage ) override;

    /** Read the style for the current layer from the Dom node supplied.
     * @param node node that will contain the style definition for this layer.
     * @param errorMessage reference to string that will be updated with any error messages
     * @return true in case of success.
     */
    bool readStyle( const QDomNode& node, QString& errorMessage ) override;

    /** Write the symbology for the layer into the docment provided.
     *  @param node the node that will have the style element added to it.
     *  @param doc the document that will have the QDomNode added.
     *  @param errorMessage reference to string that will be updated with any error messages
     *  @return true in case of success.
     */
    bool writeSymbology( QDomNode& node, QDomDocument& doc, QString& errorMessage ) const override;

    /** Write just the style information for the layer into the document
     *  @param node the node that will have the style element added to it.
     *  @param doc the document that will have the QDomNode added.
     *  @param errorMessage reference to string that will be updated with any error messages
     *  @return true in case of success.
     */
    bool writeStyle( QDomNode& node, QDomDocument& doc, QString& errorMessage ) const override;

    /**
     * Writes the symbology of the layer into the document provided in SLD 1.1 format
     * @param node the node that will have the style element added to it.
     * @param doc the document that will have the QDomNode added.
     * @param errorMessage reference to string that will be updated with any error messages
     * @param props a open ended set of properties that can drive/inform the SLD encoding
     * @return true in case of success
     */
    bool writeSld( QDomNode& node, QDomDocument& doc, QString& errorMessage, const QgsStringMap &props = QgsStringMap() ) const;

    bool readSld( const QDomNode& node, QString& errorMessage ) override;

    /**
     * Number of features rendered with specified symbol. Features must be first
     * calculated by countSymbolFeatures()
     * @param symbol the symbol
     * @return number of features rendered by symbol or -1 if failed or counts are not available
     */
    long featureCount( QgsSymbol* symbol ) const;

    /**
     * Update the data source of the layer. The layer's renderer and legend will be preserved only
     * if the geometry type of the new data source matches the current geometry type of the layer.
     * @param dataSource new layer data source
     * @param baseName base name of the layer
     * @param provider provider string
     * @param loadDefaultStyleFlag set to true to reset the layer's style to the default for the
     * data source
     * @note added in QGIS 2.10
     */
    void setDataSource( const QString& dataSource, const QString& baseName, const QString& provider, bool loadDefaultStyleFlag = false );

    /**
     * Count features for symbols. Feature counts may be get by featureCount( QgsSymbol*).
     * @param showProgress show progress dialog
     * @return true if calculated, false if failed or was canceled by user
     */
    bool countSymbolFeatures( bool showProgress = true );

    /**
     * Set the string (typically sql) used to define a subset of the layer
     * @param subset The subset string. This may be the where clause of a sql statement
     *               or other defintion string specific to the underlying dataprovider
     *               and data store.
     * @return true, when setting the subset string was successful, false otherwise
     */
    virtual bool setSubsetString( const QString& subset );

    /**
     * Get the string (typically sql) used to define a subset of the layer
     * @return The subset string or QString::null if not implemented by the provider
     */
    virtual QString subsetString() const;

    /**
     * Query the layer for features specified in request.
     * @param request feature request describing parameters of features to return
     * @returns iterator for matching features from provider
     */
    QgsFeatureIterator getFeatures( const QgsFeatureRequest& request = QgsFeatureRequest() ) const;

    /**
     * Query the layer for features matching a given expression.
     */
    inline QgsFeatureIterator getFeatures( const QString& expression )
    {
      return getFeatures( QgsFeatureRequest( expression ) );
    }

    /**
     * Query the layer for the feature with the given id.
     * If there is no such feature, the returned feature will be invalid.
     */
    inline QgsFeature getFeature( QgsFeatureId fid )
    {
      QgsFeature feature;
      getFeatures( QgsFeatureRequest( fid ) ).nextFeature( feature );
      return feature;
    }

    /**
     * Query the layer for the features with the given ids.
     */
    inline QgsFeatureIterator getFeatures( const QgsFeatureIds& fids )
    {
      return getFeatures( QgsFeatureRequest( fids ) );
    }

    /**
     * Query the layer for the features which intersect the specified rectangle.
     */
    inline QgsFeatureIterator getFeatures( const QgsRectangle& rectangle )
    {
      return getFeatures( QgsFeatureRequest( rectangle ) );
    }

    /** Adds a feature
        @param feature feature to add
        @param alsoUpdateExtent If True, will also go to the effort of e.g. updating the extents.
        @return                    True in case of success and False in case of error
     */
    bool addFeature( QgsFeature& feature, bool alsoUpdateExtent = true );

    /** Updates an existing feature. This method needs to query the datasource
        on every call. Consider using {@link changeAttributeValue()} or
        {@link changeGeometry()} instead.
        @param f  Feature to update
        @return   True in case of success and False in case of error
     */
    bool updateFeature( QgsFeature &f );

    /** Insert a new vertex before the given vertex number,
     *  in the given ring, item (first number is index 0), and feature
     *  Not meaningful for Point geometries
     */
    bool insertVertex( double x, double y, QgsFeatureId atFeatureId, int beforeVertex );

    /** Moves the vertex at the given position number,
     *  ring and item (first number is index 0), and feature
     *  to the given coordinates
     */
    bool moveVertex( double x, double y, QgsFeatureId atFeatureId, int atVertex );

    /** Moves the vertex at the given position number,
     * ring and item (first number is index 0), and feature
     * to the given coordinates
     * @note available in python as moveVertexV2
     */
    bool moveVertex( const QgsPointV2& p, QgsFeatureId atFeatureId, int atVertex );

    /** Deletes a vertex from a feature.
     * @param featureId ID of feature to remove vertex from
     * @param vertex index of vertex to delete
     * @note added in QGIS 2.14
     */
    EditResult deleteVertex( QgsFeatureId featureId, int vertex );

    /** Deletes the selected features
     *  @return true in case of success and false otherwise
     */
    bool deleteSelectedFeatures( int *deletedCount = nullptr );

    /** Adds a ring to polygon/multipolygon features
     * @param ring ring to add
     * @param featureId if specified, feature ID for feature ring was added to will be stored in this parameter
     * @return
     *  0 in case of success,
     *  1 problem with feature type,
     *  2 ring not closed,
     *  3 ring not valid,
     *  4 ring crosses existing rings,
     *  5 no feature found where ring can be inserted
     *  6 layer not editable
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int addRing( const QList<QgsPoint>& ring, QgsFeatureId* featureId = nullptr );

    /** Adds a ring to polygon/multipolygon features (takes ownership)
     * @param ring ring to add
     * @param featureId if specified, feature ID for feature ring was added to will be stored in this parameter
     * @return
     *  0 in case of success
     *  1 problem with feature type
     *  2 ring not closed
     *  6 layer not editable
     * @note available in python as addCurvedRing
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int addRing( QgsCurve* ring, QgsFeatureId* featureId = nullptr );

    /** Adds a new part polygon to a multipart feature
     * @return
     *   0 in case of success,
     *   1 if selected feature is not multipart,
     *   2 if ring is not a valid geometry,
     *   3 if new polygon ring not disjoint with existing rings,
     *   4 if no feature was selected,
     *   5 if several features are selected,
     *   6 if selected geometry not found
     *   7 layer not editable
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int addPart( const QList<QgsPoint>& ring );

    /** Adds a new part polygon to a multipart feature
     * @return
     *   0 in case of success,
     *   1 if selected feature is not multipart,
     *   2 if ring is not a valid geometry,
     *   3 if new polygon ring not disjoint with existing rings,
     *   4 if no feature was selected,
     *   5 if several features are selected,
     *   6 if selected geometry not found
     *   7 layer not editable
     * @note available in python bindings as addPartV2
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int addPart( const QgsPointSequence &ring );

    //! @note available in python as addCurvedPart
    int addPart( QgsCurve* ring );

    /** Translates feature by dx, dy
     *  @param featureId id of the feature to translate
     *  @param dx translation of x-coordinate
     *  @param dy translation of y-coordinate
     *  @return 0 in case of success
     */
    int translateFeature( QgsFeatureId featureId, double dx, double dy );

    /** Splits parts cut by the given line
     *  @param splitLine line that splits the layer features
     *  @param topologicalEditing true if topological editing is enabled
     *  @return
     *   0 in case of success,
     *   4 if there is a selection but no feature split
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int splitParts( const QList<QgsPoint>& splitLine, bool topologicalEditing = false );

    /** Splits features cut by the given line
     *  @param splitLine line that splits the layer features
     *  @param topologicalEditing true if topological editing is enabled
     *  @return
     *   0 in case of success,
     *   4 if there is a selection but no feature split
     */
    // TODO QGIS 3.0 returns an enum instead of a magic constant
    int splitFeatures( const QList<QgsPoint>& splitLine, bool topologicalEditing = false );

    /** Adds topological points for every vertex of the geometry.
     * @param geom the geometry where each vertex is added to segments of other features
     * @note geom is not going to be modified by the function
     * @return 0 in case of success
     */
    int addTopologicalPoints( const QgsGeometry& geom );

    /** Adds a vertex to segments which intersect point p but don't
     * already have a vertex there. If a feature already has a vertex at position p,
     * no additional vertex is inserted. This method is useful for topological
     * editing.
     * @param p position of the vertex
     * @return 0 in case of success
     */
    int addTopologicalPoints( const QgsPoint& p );

    /** Inserts vertices to the snapped segments.
     * This is useful for topological editing if snap to segment is enabled.
     * @param snapResults results collected from the snapping operation
     * @return 0 in case of success
     */
    int insertSegmentVerticesForSnap( const QList<QgsSnappingResult>& snapResults );

    /** Access to labeling configuration.
     * @note added in 2.12
     * @note not available in Python bindings
     */
    const QgsAbstractVectorLayerLabeling* labeling() const { return mLabeling; }

    /** Set labeling configuration. Takes ownership of the object.
     * @note added in 2.12
     * @note not available in Python bindings
     */
    void setLabeling( QgsAbstractVectorLayerLabeling* labeling );

    //! Returns true if the provider is in editing mode
    virtual bool isEditable() const override;

    virtual bool isSpatial() const override;

    //! Returns true if the provider has been modified since the last commit
    virtual bool isModified() const;

    /** Snaps a point to the closest vertex if there is one within the snapping tolerance
     *  @param point       The point which is set to the position of a vertex if there is one within the snapping tolerance.
     *  If there is no point within this tolerance, point is left unchanged.
     *  @param tolerance   The snapping tolerance
     *  @return true if the point has been snapped, false if no vertex within search tolerance
     */
    bool snapPoint( QgsPoint& point, double tolerance );

    /** Snaps to segment or vertex within given tolerance
     * @param startPoint point to snap (in layer coordinates)
     * @param snappingTolerance distance tolerance for snapping
     * @param snappingResults snapping results. Key is the distance between startPoint and snapping target
     * @param snap_to to segment / to vertex
     * @return 0 in case of success
     */
    int snapWithContext( const QgsPoint& startPoint,
                         double snappingTolerance,
                         QMultiMap < double, QgsSnappingResult > &snappingResults,
                         QgsSnapper::SnappingType snap_to );

    //! Synchronises with changes in the datasource
    virtual void reload() override;

    /** Return new instance of QgsMapLayerRenderer that will be used for rendering of given context
     * @note added in 2.4
     */
    virtual QgsMapLayerRenderer* createMapRenderer( QgsRenderContext& rendererContext ) override;

    //! Return the extent of the layer
    QgsRectangle extent() const override;

    /**
     * Returns the list of fields of this layer.
     * This also includes fields which have not yet been saved to the provider.
     *
     * @return A list of fields
     */
    inline QgsFields fields() const { return mFields; }

    /**
     * Returns the list of fields of this layer.
     * This also includes fields which have not yet been saved to the provider.
     * Alias for {@link fields()}
     *
     * @return A list of fields
     */
    inline QgsFields pendingFields() const { return mFields; }

    /**
     * Returns list of attribute indexes. i.e. a list from 0 ... fieldCount()
     * Alias for {@link attributeList()}
     */
    inline QgsAttributeList pendingAllAttributesList() const { return mFields.allAttributesList(); }

    /**
     * Returns list of attribute indexes. i.e. a list from 0 ... fieldCount()
     * Alias for {@link attributeList()}
     */
    inline QgsAttributeList attributeList() const { return mFields.allAttributesList(); }

    /**
     * Returns list of attributes making up the primary key
     * Alias for {@link pkAttributeList()}
     */
    inline QgsAttributeList pendingPkAttributesList() const { return pkAttributeList(); }

    //! Returns list of attributes making up the primary key
    QgsAttributeList pkAttributeList() const;

    /**
     * Returns feature count including changes which have not yet been committed
     * Alias for {@link featureCount()}
     */
    inline long pendingFeatureCount() const { return featureCount(); }

    /**
     * Returns feature count including changes which have not yet been committed
     * If you need only the count of committed features call this method on this layer's provider.
     */
    long featureCount() const;

    /** Make layer read-only (editing disabled) or not
     *  @return false if the layer is in editing yet
     */
    bool setReadOnly( bool readonly = true );

    //! Change feature's geometry
    bool changeGeometry( QgsFeatureId fid, const QgsGeometry& geom );

    /**
     * Changes an attribute value (but does not commit it)
     *
     * @param fid   The feature id of the feature to be changed
     * @param field The index of the field to be updated
     * @param newValue The value which will be assigned to the field
     * @param oldValue The previous value to restore on undo (will otherwise be retrieved)
     *
     * @return true in case of success
     */
    bool changeAttributeValue( QgsFeatureId fid, int field, const QVariant &newValue, const QVariant &oldValue = QVariant() );

    /** Add an attribute field (but does not commit it)
     * returns true if the field was added
     */
    bool addAttribute( const QgsField &field );

    /**
     * Sets an alias (a display name) for attributes to display in dialogs
     *
     * @note Added in QGIS 3.0
     */
    void setFieldAlias( int index, const QString& aliasString );

    /**
     * Removes an alias (a display name) for attributes to display in dialogs
     *
     * @note Added in QGIS 3.0
     */
    void removeFieldAlias( int index );

    /** Renames an attribute field  (but does not commit it).
     * @param index attribute index
     * @param newName new name of field
     * @note added in QGIS 2.16
     */
    bool renameAttribute( int index, const QString& newName );

    /**
     * Returns the alias of an attribute name or a null string if there is no alias.
     *
     * @see {attributeDisplayName( int attributeIndex )} which returns the field name
     *      if no alias is defined.
     */
    QString attributeAlias( int index ) const;

    //! Convenience function that returns the attribute alias if defined or the field name else
    QString attributeDisplayName( int index ) const;

    //! Returns a map of field name to attribute alias
    QgsStringMap attributeAliases() const;

    /**
     * A set of attributes that are not advertised in WMS requests with QGIS server.
     */
    const QSet<QString>& excludeAttributesWms() const { return mExcludeAttributesWMS; }
    /**
     * A set of attributes that are not advertised in WMS requests with QGIS server.
     */
    void setExcludeAttributesWms( const QSet<QString>& att ) { mExcludeAttributesWMS = att; }

    /**
     * A set of attributes that are not advertised in WFS requests with QGIS server.
     */
    const QSet<QString>& excludeAttributesWfs() const { return mExcludeAttributesWFS; }

    /**
     * A set of attributes that are not advertised in WFS requests with QGIS server.
     */
    void setExcludeAttributesWfs( const QSet<QString>& att ) { mExcludeAttributesWFS = att; }

    //! Delete an attribute field (but does not commit it)
    bool deleteAttribute( int attr );

    /**
     * Deletes a list of attribute fields (but does not commit it)
     *
     * @param  attrs the indices of the attributes to delete
     * @return true if at least one attribute has been deleted
     *
     */
    bool deleteAttributes( QList<int> attrs );

    //! Insert a copy of the given features into the layer  (but does not commit it)
    bool addFeatures( QgsFeatureList features, bool makeSelected = true );

    //! Delete a feature from the layer (but does not commit it)
    bool deleteFeature( QgsFeatureId fid );

    /**
     * Deletes a set of features from the layer (but does not commit it)
     * @param fids The feature ids to delete
     *
     * @return false if the layer is not in edit mode or does not support deleting
     *         in case of an active transaction depends on the provider implementation
     */
    bool deleteFeatures( const QgsFeatureIds& fids );

    /**
     * Attempts to commit any changes to disk.  Returns the result of the attempt.
     * If a commit fails, the in-memory changes are left alone.
     *
     * This allows editing to continue if the commit failed on e.g. a
     * disallowed value in a Postgres database - the user can re-edit and try
     * again.
     *
     * The commits occur in distinct stages,
     * (add attributes, add features, change attribute values, change
     * geometries, delete features, delete attributes)
     * so if a stage fails, it's difficult to roll back cleanly.
     * Therefore any error message also includes which stage failed so
     * that the user has some chance of repairing the damage cleanly.
     * @see commitErrors()
     */
    bool commitChanges();

    /** Returns a list containing any error messages generated when attempting
     * to commit changes to the layer.
     * @see commitChanges()
     */
    QStringList commitErrors() const;

    /** Stop editing and discard the edits
     * @param deleteBuffer whether to delete editing buffer
     */
    bool rollBack( bool deleteBuffer = true );

    //! Get annotation form
    QString annotationForm() const { return mAnnotationForm; }

    //! Set annotation form for layer
    void setAnnotationForm( const QString& ui );

    /**
     * Get relations, where the foreign key is on this layer
     *
     * @param idx Only get relations, where idx forms part of the foreign key
     * @return A list of relations
     */
    QList<QgsRelation> referencingRelations( int idx ) const;

    //! Buffer with uncommitted editing operations. Only valid after editing has been turned on.
    QgsVectorLayerEditBuffer* editBuffer() { return mEditBuffer; }

    //! Buffer with uncommitted editing operations. Only valid after editing has been turned on.
    const QgsVectorLayerEditBuffer* editBuffer() const { return mEditBuffer; }

    /**
     * Create edit command for undo/redo operations
     * @param text text which is to be displayed in undo window
     */
    void beginEditCommand( const QString& text );

    //! Finish edit command and add it to undo/redo stack
    void endEditCommand();

    //! Destroy active command and reverts all changes in it
    void destroyEditCommand();

    //! Editing vertex markers
    enum VertexMarkerType
    {
      SemiTransparentCircle,
      Cross,
      NoMarker
    };

    //! Draws a vertex symbol at (screen) coordinates x, y. (Useful to assist vertex editing.)
    static void drawVertexMarker( double x, double y, QPainter& p, QgsVectorLayer::VertexMarkerType type, int vertexSize );

    //! Assembles mUpdatedFields considering provider fields, joined fields and added fields
    void updateFields();

    //! Caches joined attributes if required (and not already done)
    // marked as const as these are just caches, and need to be created from const accessors
    void createJoinCaches() const;

    /** Returns the calculated default value for the specified field index. The default
     * value may be taken from a client side default value expression (see setDefaultValueExpression())
     * or taken from the underlying data provider.
     * @param index field index
     * @param feature optional feature to use for default value evaluation. If passed,
     * then properties from the feature (such as geometry) can be used when calculating
     * the default value.
     * @param context optional expression context to evaluate expressions again. If not
     * specified, a default context will be created
     * @return calculated default value
     * @note added in QGIS 3.0
     * @see setDefaultValueExpression()
     */
    QVariant defaultValue( int index, const QgsFeature& feature = QgsFeature(),
                           QgsExpressionContext* context = nullptr ) const;

    /** Sets an expression to use when calculating the default value for a field.
     * @param index field index
     * @param expression expression to evaluate when calculating default values for field. Pass
     * an empty expression to clear the default.
     * @note added in QGIS 3.0
     * @see defaultValue()
     * @see defaultValueExpression()
     */
    void setDefaultValueExpression( int index, const QString& expression );

    /** Returns the expression used when calculating the default value for a field.
     * @param index field index
     * @returns expression evaluated when calculating default values for field, or an
     * empty string if no default is set
     * @note added in QGIS 3.0
     * @see defaultValue()
     * @see setDefaultValueExpression()
     */
    QString defaultValueExpression( int index ) const;

    /**
     * Returns any constraints which are present for a specified
     * field index. These constraints may be inherited from the layer's data provider
     * or may be set manually on the vector layer from within QGIS.
     * @note added in QGIS 3.0
     * @see setFieldConstraints()
     */
    QgsField::Constraints fieldConstraints( int fieldIndex ) const;

    /**
     * Sets the constraints for a specified field index. Any constraints inherited from the layer's
     * data provider will be kept intact and cannot be cleared. Ie, calling this method only allows for new
     * constraints to be added on top of the existing provider constraints.
     * @note added in QGIS 3.0
     * @see fieldConstraints()
     */
    void setFieldConstraints( int index, QgsField::Constraints constraints );

    /** Calculates a list of unique values contained within an attribute in the layer. Note that
     * in some circumstances when unsaved changes are present for the layer then the returned list
     * may contain outdated values (for instance when the attribute value in a saved feature has
     * been changed inside the edit buffer then the previous saved value will be included in the
     * returned list).
     * @param index column index for attribute
     * @param uniqueValues out: result list
     * @param limit maximum number of values to return (or -1 if unlimited)
     * @see minimumValue()
     * @see maximumValue()
     */
    void uniqueValues( int index, QList<QVariant> &uniqueValues, int limit = -1 ) const;

    /** Returns the minimum value for an attribute column or an invalid variant in case of error.
     * Note that in some circumstances when unsaved changes are present for the layer then the
     * returned value may be outdated (for instance when the attribute value in a saved feature has
     * been changed inside the edit buffer then the previous saved value may be returned as the minimum).
     * @see maximumValue()
     * @see uniqueValues()
     */
    QVariant minimumValue( int index ) const;

    /** Returns the maximum value for an attribute column or an invalid variant in case of error.
     * Note that in some circumstances when unsaved changes are present for the layer then the
     * returned value may be outdated (for instance when the attribute value in a saved feature has
     * been changed inside the edit buffer then the previous saved value may be returned as the maximum).
     * @see minimumValue()
     * @see uniqueValues()
     */
    QVariant maximumValue( int index ) const;

    /** Calculates an aggregated value from the layer's features.
     * @param aggregate aggregate to calculate
     * @param fieldOrExpression source field or expression to use as basis for aggregated values.
     * @param parameters parameters controlling aggregate calculation
     * @param context expression context for expressions and filters
     * @param ok if specified, will be set to true if aggregate calculation was successful
     * @return calculated aggregate value
     * @note added in QGIS 2.16
     */
    QVariant aggregate( QgsAggregateCalculator::Aggregate aggregate,
                        const QString& fieldOrExpression,
                        const QgsAggregateCalculator::AggregateParameters& parameters = QgsAggregateCalculator::AggregateParameters(),
                        QgsExpressionContext* context = nullptr,
                        bool* ok = nullptr ) const;

    /** Fetches all values from a specified field name or expression.
     * @param fieldOrExpression field name or an expression string
     * @param ok will be set to false if field or expression is invalid, otherwise true
     * @param selectedOnly set to true to get values from selected features only
     * @returns list of fetched values
     * @note added in QGIS 2.9
     * @see getDoubleValues
     */
    QList< QVariant > getValues( const QString &fieldOrExpression, bool &ok, bool selectedOnly = false ) const;

    /** Fetches all double values from a specified field name or expression. Null values or
     * invalid expression results are skipped.
     * @param fieldOrExpression field name or an expression string evaluating to a double value
     * @param ok will be set to false if field or expression is invalid, otherwise true
     * @param selectedOnly set to true to get values from selected features only
     * @param nullCount optional pointer to integer to store number of null values encountered in
     * @returns list of fetched values
     * @note added in QGIS 2.9
     * @see getValues
     */
    QList< double > getDoubleValues( const QString &fieldOrExpression, bool &ok, bool selectedOnly = false, int* nullCount = nullptr ) const;

    //! Set the blending mode used for rendering each feature
    void setFeatureBlendMode( QPainter::CompositionMode blendMode );
    //! Returns the current blending mode for features
    QPainter::CompositionMode featureBlendMode() const;

    //! Set the transparency for the vector layer
    void setLayerTransparency( int layerTransparency );
    //! Returns the current transparency for the vector layer
    int layerTransparency() const;

    QString metadata() const override;

    //! @note not available in python bindings
    inline QgsGeometryCache* cache() { return mCache; }

    /** Set the simplification settings for fast rendering of features
     *  @note added in 2.2
     */
    void setSimplifyMethod( const QgsVectorSimplifyMethod& simplifyMethod ) { mSimplifyMethod = simplifyMethod; }

    /** Returns the simplification settings for fast rendering of features
     *  @note added in 2.2
     */
    inline const QgsVectorSimplifyMethod& simplifyMethod() const { return mSimplifyMethod; }

    /** Returns whether the VectorLayer can apply the specified simplification hint
     *  @note Do not use in 3rd party code - may be removed in future version!
     *  @note added in 2.2
     */
    bool simplifyDrawingCanbeApplied( const QgsRenderContext& renderContext, QgsVectorSimplifyMethod::SimplifyHint simplifyHint ) const;

    /**
     * @brief Return the conditional styles that are set for this layer. Style information is
     * used to render conditional formatting in the attribute table.
     * @return Return a QgsConditionalLayerStyles object holding the conditional attribute
     * style information. Style information is generic and can be used for anything.
     * @note added in QGIS 2.12
     */
    QgsConditionalLayerStyles *conditionalStyles() const;

    /**
     * Get the attribute table configuration object.
     * This defines the appearance of the attribute table.
     */
    QgsAttributeTableConfig attributeTableConfig() const;

    /**
     * Set the attribute table configuration object.
     * This defines the appearance of the attribute table.
     */
    void setAttributeTableConfig( const QgsAttributeTableConfig& attributeTableConfig );

    /**
     * The mapTip is a pretty, html representation for feature information.
     *
     * It may also contain embedded expressions.
     *
     * @note added in 3.0
     */
    QString mapTipTemplate() const;

    /**
     * The mapTip is a pretty, html representation for feature information.
     *
     * It may also contain embedded expressions.
     *
     * @note added in 3.0
     */
    void setMapTipTemplate( const QString& mapTipTemplate );

    QgsExpressionContext createExpressionContext() const override;

    /**
     * Get the configuration of the form used to represent this vector layer.
     * This is a writable configuration that can directly be changed in place.
     *
     * @return The configuration of this layers' form
     *
     * @note Added in QGIS 2.14
     */
    QgsEditFormConfig editFormConfig() const;

    /**
     * Get the configuration of the form used to represent this vector layer.
     * This is a writable configuration that can directly be changed in place.
     *
     * @return The configuration of this layers' form
     *
     * @note Added in QGIS 3.0
     */
    void setEditFormConfig( const QgsEditFormConfig& editFormConfig );

  public slots:
    /**
     * Select feature by its ID
     *
     * @param featureId  The id of the feature to select
     *
     * @see select(QgsFeatureIds)
     */
    void select( QgsFeatureId featureId );

    /**
     * Select features by their ID
     *
     * @param featureIds The ids of the features to select
     *
     * @see select(QgsFeatureId)
     */
    void select( const QgsFeatureIds& featureIds );

    /**
     * Deselect feature by its ID
     *
     * @param featureId  The id of the feature to deselect
     *
     * @see deselect(QgsFeatureIds)
     */
    void deselect( const QgsFeatureId featureId );

    /**
     * Deselect features by their ID
     *
     * @param featureIds The ids of the features to deselect
     *
     * @see deselect(QgsFeatureId)
     */
    void deselect( const QgsFeatureIds& featureIds );

    /**
     * Clear selection
     *
     * @see selectByIds()
     */
    void removeSelection();

    /** Update the extents for the layer. This is necessary if features are
     *  added/deleted or the layer has been subsetted.
     */
    virtual void updateExtents();

    //! Check if there is a join with a layer that will be removed
    void checkJoinLayerRemove( const QString& theLayerId );

    /**
     * Make layer editable.
     * This starts an edit session on this layer. Changes made in this edit session will not
     * be made persistent until {@link commitChanges()} is called and can be reverted by calling
     * {@link rollBack()}.
     */
    bool startEditing();


  protected slots:
    void invalidateSymbolCountedFlag();

  signals:

    /**
     * This signal is emitted when selection was changed
     *
     * @param selected        Newly selected feature ids
     * @param deselected      Ids of all features which have previously been selected but are not any more
     * @param clearAndSelect  In case this is set to true, the old selection was dismissed and the new selection corresponds to selected
     */
    void selectionChanged( const QgsFeatureIds& selected, const QgsFeatureIds& deselected, const bool clearAndSelect );

    //! This signal is emitted when selection was changed
    void selectionChanged();

    //! This signal is emitted when modifications has been done on layer
    void layerModified();

    //! Is emitted, when layer is checked for modifications. Use for last-minute additions
    void beforeModifiedCheck() const;

    //! Is emitted, before editing on this layer is started
    void beforeEditingStarted();

    //! Is emitted, when editing on this layer has started
    void editingStarted();

    //! Is emitted, when edited changes successfully have been written to the data provider
    void editingStopped();

    //! Is emitted, before changes are commited to the data provider
    void beforeCommitChanges();

    //! Is emitted, before changes are rolled back
    void beforeRollBack();

    /**
     * Will be emitted, when a new attribute has been added to this vector layer.
     * Applies only to types {@link QgsFields::OriginEdit}, {@link QgsFields::OriginProvider} and {@link QgsFields::OriginExpression }
     *
     * @param idx The index of the new attribute
     *
     * @see updatedFields()
     */
    void attributeAdded( int idx );

    /**
     * Will be emitted, when an expression field is going to be added to this vector layer.
     * Applies only to types {@link QgsFields::OriginExpression }
     *
     * @param fieldName The name of the attribute to be added
     */
    void beforeAddingExpressionField( const QString& fieldName );

    /**
     * Will be emitted, when an attribute has been deleted from this vector layer.
     * Applies only to types {@link QgsFields::OriginEdit}, {@link QgsFields::OriginProvider} and {@link QgsFields::OriginExpression }
     *
     * @param idx The index of the deleted attribute
     *
     * @see updatedFields()
     */
    void attributeDeleted( int idx );

    /**
     * Will be emitted, when an expression field is going to be deleted from this vector layer.
     * Applies only to types {@link QgsFields::OriginExpression }
     *
     * @param idx The index of the attribute to be deleted
     */
    void beforeRemovingExpressionField( int idx );

    /**
     * Emitted when a new feature has been added to the layer
     *
     * @param fid The id of the new feature
     */
    void featureAdded( QgsFeatureId fid );

    /**
     * Emitted when a feature has been deleted.
     *
     * If you do expensive operations in a slot connected to this, you should prever to use
     * {@link featuresDeleted( const QgsFeatureIds& )}.
     *
     * @param fid The id of the feature which has been deleted
     */
    void featureDeleted( QgsFeatureId fid );

    /**
     * Emitted when features have been deleted.
     *
     * If features are deleted within an edit command, this will only be emitted once at the end
     * to allow connected slots to minimize the overhead.
     * If features are deleted outside of an edit command, this signal will be emitted once per feature.
     *
     * @param fids The feature ids that have been deleted.
     */
    void featuresDeleted( const QgsFeatureIds& fids );

    /**
     * Is emitted, whenever the fields available from this layer have been changed.
     * This can be due to manually adding attributes or due to a join.
     */
    void updatedFields();


    /**
     * Is emitted whenever an attribute value change is done in the edit buffer.
     * Note that at this point the attribute change is not yet saved to the provider.
     *
     * @param fid The id of the changed feature
     * @param idx The attribute index of the changed attribute
     * @param value The new value of the attribute
     */
    void attributeValueChanged( QgsFeatureId fid, int idx, const QVariant& value );

    /**
     * Is emitted whenever a geometry change is done in the edit buffer.
     * Note that at this point the geometry change is not yet saved to the provider.
     *
     * @param fid The id of the changed feature
     * @param geometry The new geometry
     */
    void geometryChanged( QgsFeatureId fid, const QgsGeometry& geometry );

    //! This signal is emitted, when attributes are deleted from the provider
    void committedAttributesDeleted( const QString& layerId, const QgsAttributeList& deletedAttributes );
    //! This signal is emitted, when attributes are added to the provider
    void committedAttributesAdded( const QString& layerId, const QList<QgsField>& addedAttributes );
    //! This signal is emitted, when features are added to the provider
    void committedFeaturesAdded( const QString& layerId, const QgsFeatureList& addedFeatures );
    //! This signal is emitted, when features are deleted from the provider
    void committedFeaturesRemoved( const QString& layerId, const QgsFeatureIds& deletedFeatureIds );
    //! This signal is emitted, when attribute value changes are saved to the provider
    void committedAttributeValuesChanges( const QString& layerId, const QgsChangedAttributesMap& changedAttributesValues );
    //! This signal is emitted, when geometry changes are saved to the provider
    void committedGeometriesChanges( const QString& layerId, const QgsGeometryMap& changedGeometries );

    //! Emitted when the font family defined for labeling layer is not found on system
    void labelingFontNotFound( QgsVectorLayer* layer, const QString& fontfamily );

    //! Signal emitted when setFeatureBlendMode() is called
    void featureBlendModeChanged( QPainter::CompositionMode blendMode );

    //! Signal emitted when setLayerTransparency() is called
    void layerTransparencyChanged( int layerTransparency );

    /**
     * Signal emitted when a new edit command has been started
     *
     * @param text Description for this edit command
     */
    void editCommandStarted( const QString& text );

    /**
     * Signal emitted, when an edit command successfully ended
     * @note This does not mean it is also committed, only that it is written
     * to the edit buffer. See {@link beforeCommitChanges()}
     */
    void editCommandEnded();

    /**
     * Signal emitted, whan an edit command is destroyed
     * @note This is not a rollback, it is only related to the current edit command.
     * See {@link beforeRollBack()}
     */
    void editCommandDestroyed();

    /**
     * Signal emitted whenever the symbology (QML-file) for this layer is being read.
     * If there is custom style information saved in the file, you can connect to this signal
     * and update the layer style accordingly.
     *
     * @param element The XML layer style element.
     *
     * @param errorMessage Write error messages into this string.
     */
    void readCustomSymbology( const QDomElement& element, QString& errorMessage );

    /**
     * Signal emitted whenever the symbology (QML-file) for this layer is being written.
     * If there is custom style information you want to save to the file, you can connect
     * to this signal and update the element accordingly.
     *
     * @param element  The XML element where you can add additional style information to.
     * @param doc      The XML document that you can use to create new XML nodes.
     * @param errorMessage Write error messages into this string.
     */
    void writeCustomSymbology( QDomElement& element, QDomDocument& doc, QString& errorMessage ) const;

    /**
     * Emitted when the map tip changes
     *
     * @note added in QGIS 3.0
     */
    void mapTipTemplateChanged();

    /**
     * Emitted when the display expression changes
     *
     * @note added in QGIS 3.0
     */
    void displayExpressionChanged();

    /**
     * Signals an error related to this vector layer.
     */
    void raiseError( const QString& msg );

    /**
     * Will be emitted whenever the edit form configuration of this layer changes.
     *
     * @note added in QGIS 3.0
     */
    void editFormConfigChanged();

    /**
     * Emitted when the read only state of this layer is changed.
     * Only applies to manually set readonly state, not to the edit mode.
     *
     * @note Added in QGIS 3.0
     */
    void readOnlyChanged();


  private slots:
    void onJoinedFieldsChanged();
    void onFeatureDeleted( QgsFeatureId fid );
    void onRelationsLoaded();

  protected:
    //! Set the extent
    void setExtent( const QgsRectangle &rect ) override;

  private:                       // Private methods
    /**
     * Returns true if the provider is in read-only mode
     */
    virtual bool isReadOnly() const override;

    //! Vector layers are not copyable
    QgsVectorLayer( const QgsVectorLayer & rhs );

    //! Vector layers are not copyable
    QgsVectorLayer & operator=( QgsVectorLayer const & rhs );


    /** Bind layer to a specific data provider
     * @param provider should be "postgres", "ogr", or ??
     * @todo XXX should this return bool?  Throw exceptions?
     */
    bool setDataProvider( QString const & provider );

    //! Goes through all features and finds a free id (e.g. to give it temporarily to a not-commited feature)
    QgsFeatureId findFreeId();

    /** Snaps to a geometry and adds the result to the multimap if it is within the snapping result
     * @param startPoint start point of the snap
     * @param featureId id of feature
     * @param geom geometry to snap
     * @param sqrSnappingTolerance squared search tolerance of the snap
     * @param snappingResults list to which the result is appended
     * @param snap_to snap to vertex or to segment
     */
    void snapToGeometry( const QgsPoint& startPoint,
                         QgsFeatureId featureId,
                         const QgsGeometry& geom,
                         double sqrSnappingTolerance,
                         QMultiMap<double, QgsSnappingResult>& snappingResults,
                         QgsSnapper::SnappingType snap_to ) const;

    //! Add joined attributes to a feature
    //void addJoinedAttributes( QgsFeature& f, bool all = false );

    //! Read labeling from SLD
    void readSldLabeling( const QDomNode& node );

  private:                       // Private attributes

    QgsConditionalLayerStyles * mConditionalStyles;

    //! Pointer to data provider derived from the abastract base class QgsDataProvider
    QgsVectorDataProvider *mDataProvider;

    //! The preview expression used to generate a human readable preview string for features
    QString mDisplayExpression;

    QString mMapTipTemplate;

    //! Data provider key
    QString mProviderKey;

    //! The user-defined actions that are accessed from the Identify Results dialog box
    QgsActionManager* mActions;

    //! Flag indicating whether the layer is in read-only mode (editing disabled) or not
    bool mReadOnly;

    /** Set holding the feature IDs that are activated.  Note that if a feature
        subsequently gets deleted (i.e. by its addition to mDeletedFeatureIds),
        it always needs to be removed from mSelectedFeatureIds as well.
     */
    QgsFeatureIds mSelectedFeatureIds;

    //! Field map to commit
    QgsFields mFields;

    //! Map that stores the aliases for attributes. Key is the attribute name and value the alias for that attribute
    QgsStringMap mAttributeAliasMap;

    //! Map which stores default value expressions for fields
    QgsStringMap mDefaultExpressionMap;

    //! Map which stores constraints for fields
    QMap< QString, QgsField::Constraints > mFieldConstraints;

    //! Holds the configuration for the edit form
    QgsEditFormConfig mEditFormConfig;

    //! Attributes which are not published in WMS
    QSet<QString> mExcludeAttributesWMS;

    //! Attributes which are not published in WFS
    QSet<QString> mExcludeAttributesWFS;

    //! Geometry type as defined in enum WkbType (qgis.h)
    QgsWkbTypes::Type mWkbType;

    //! Renderer object which holds the information about how to display the features
    QgsFeatureRenderer *mRenderer;

    //! Simplification object which holds the information about how to simplify the features for fast rendering
    QgsVectorSimplifyMethod mSimplifyMethod;

    //! Labeling configuration
    QgsAbstractVectorLayerLabeling* mLabeling;

    //! Whether 'labeling font not found' has be shown for this layer (only show once in QgsMessageBar, on first rendering)
    bool mLabelFontNotFoundNotified;

    //! Blend mode for features
    QPainter::CompositionMode mFeatureBlendMode;

    //! Layer transparency
    int mLayerTransparency;

    //! Flag if the vertex markers should be drawn only for selection (true) or for all features (false)
    bool mVertexMarkerOnlyForSelection;

    QStringList mCommitErrors;

    //! Annotation form for this layer
    QString mAnnotationForm;

    //! cache for some vector layer data - currently only geometries for faster editing
    QgsGeometryCache* mCache;

    //! stores information about uncommitted changes to layer
    QgsVectorLayerEditBuffer* mEditBuffer;
    friend class QgsVectorLayerEditBuffer;

    //stores information about joined layers
    QgsVectorLayerJoinBuffer* mJoinBuffer;

    //! stores information about expression fields on this layer
    QgsExpressionFieldBuffer* mExpressionFieldBuffer;

    //diagram rendering object. 0 if diagram drawing is disabled
    QgsDiagramRenderer* mDiagramRenderer;

    //stores infos about diagram placement (placement type, priority, position distance)
    QgsDiagramLayerSettings *mDiagramLayerSettings;

    mutable bool mValidExtent;
    mutable bool mLazyExtent;

    // Features in renderer classes counted
    bool mSymbolFeatureCounted;

    // Feature counts for each renderer symbol
    QMap<QgsSymbol*, long> mSymbolFeatureCountMap;

    //! True while an undo command is active
    bool mEditCommandActive;

    QgsFeatureIds mDeletedFids;

    QgsAttributeTableConfig mAttributeTableConfig;

    mutable QMutex mFeatureSourceConstructorMutex;

    friend class QgsVectorLayerFeatureSource;
};

#endif