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qgsfeaturerequest.h
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qgsfeaturerequest.h
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/***************************************************************************
qgsfeaturerequest.h
---------------------
begin : Mai 2012
copyright : (C) 2012 by Martin Dobias
email : wonder dot sk at gmail dot 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 QGSFEATUREREQUEST_H
#define QGSFEATUREREQUEST_H
#include "qgis_core.h"
#include "qgis_sip.h"
#include <QFlags>
#include <QList>
#include <memory>
#include "qgsfeature.h"
#include "qgsrectangle.h"
#include "qgsexpression.h"
#include "qgsexpressioncontext.h"
#include "qgssimplifymethod.h"
/**
* \ingroup core
* This class wraps a request for features to a vector layer (or directly its vector data provider).
* The request may apply a filter to fetch only a particular subset of features. Currently supported filters:
* - no filter - all features are returned
* - feature id - only feature that matches given feature id is returned
* - feature ids - only features that match any of the given feature ids are returned
* - filter expression - only features that match the given filter expression are returned
*
* Additionally a spatial rectangle can be set in combination:
* Only features that intersect given rectangle should be fetched. For the sake of speed,
* the intersection is often done only using feature's bounding box. There is a flag
* ExactIntersect that makes sure that only intersecting features will be returned.
*
* For efficiency, it is also possible to tell provider that some data is not required:
* - NoGeometry flag
* - SubsetOfAttributes flag
* - SimplifyMethod for geometries to fetch
*
* The options may be chained, e.g.:
*
* \code{.py}
* QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1)).setFlags(QgsFeatureRequest.ExactIntersect)
* \endcode
*
* Examples:
*
* \code{.py}
* # fetch all features:
* QgsFeatureRequest()
* # fetch all features, only one attribute
* QgsFeatureRequest().setSubsetOfAttributes(['myfield'], layer.fields())
* # fetch all features, without geometries
* QgsFeatureRequest().setFlags(QgsFeatureRequest.NoGeometry)
* # fetch only features from particular extent
* QgsFeatureRequest().setFilterRect(QgsRectangle(0,0,1,1))
* # fetch only one feature
* QgsFeatureRequest().setFilterFid(45)
* \endcode
*/
class CORE_EXPORT QgsFeatureRequest
{
public:
enum Flag
{
NoFlags = 0,
NoGeometry = 1, //!< Geometry is not required. It may still be returned if e.g. required for a filter condition.
SubsetOfAttributes = 2, //!< Fetch only a subset of attributes (setSubsetOfAttributes sets this flag)
ExactIntersect = 4 //!< Use exact geometry intersection (slower) instead of bounding boxes
};
Q_DECLARE_FLAGS( Flags, Flag )
/**
* Types of filters.
*/
enum FilterType
{
FilterNone, //!< No filter is applied
FilterFid, //!< Filter using feature ID
FilterExpression, //!< Filter using expression
FilterFids //!< Filter using feature IDs
};
//! Handling of features with invalid geometries
enum InvalidGeometryCheck
{
GeometryNoCheck = 0, //!< No invalid geometry checking
GeometrySkipInvalid = 1, //!< Skip any features with invalid geometry. This requires a slow geometry validity check for every feature.
GeometryAbortOnInvalid = 2, //!< Close iterator on encountering any features with invalid geometry. This requires a slow geometry validity check for every feature.
};
/**
* \ingroup core
* The OrderByClause class represents an order by clause for a QgsFeatureRequest.
*
* It can be a simple field or an expression. Multiple order by clauses can be added to
* a QgsFeatureRequest to fine tune the behavior if a single field or expression is not
* enough to completely specify the required behavior.
*
* If expression compilation is activated in the settings and the expression can be
* translated for the provider in question, it will be evaluated on provider side.
* If one of these two premises does not apply, the ordering will take place locally
* which results in increased memory and CPU usage.
*
* If the ordering is done on strings, the order depends on the system's locale if the
* local fallback implementation is used. The order depends on the server system's locale
* and implementation if ordering is done on the server.
*
* In case the fallback code needs to be used, a limit set on the request will be respected
* for the features returned by the iterator but internally all features will be requested
* from the provider.
*
* \since QGIS 2.14
*/
class CORE_EXPORT OrderByClause
{
public:
/**
* Creates a new OrderByClause for a QgsFeatureRequest
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* If the order is ascending, by default nulls are last
* If the order is descending, by default nulls are first
*/
OrderByClause( const QString &expression, bool ascending = true );
/**
* Creates a new OrderByClause for a QgsFeatureRequest
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* \param nullsfirst If true, NULLS are at the beginning, if false, NULLS are at the end
*/
OrderByClause( const QString &expression, bool ascending, bool nullsfirst );
/**
* Creates a new OrderByClause for a QgsFeatureRequest
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* If the order is ascending, by default nulls are last
* If the order is descending, by default nulls are first
*/
OrderByClause( const QgsExpression &expression, bool ascending = true );
/**
* Creates a new OrderByClause for a QgsFeatureRequest
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* \param nullsfirst If true, NULLS are at the beginning, if false, NULLS are at the end
*/
OrderByClause( const QgsExpression &expression, bool ascending, bool nullsfirst );
/**
* The expression
* \returns the expression
*/
QgsExpression expression() const;
/**
* Prepare the expression with the given context.
*
* \see QgsExpression::prepare
*
* \since QGIS 3.0
*/
bool prepare( QgsExpressionContext *context );
/**
* Order ascending
* \returns If ascending order is requested
*/
bool ascending() const;
/**
* Set if ascending order is requested
*/
void setAscending( bool ascending );
/**
* Set if NULLS should be returned first
* \returns if NULLS should be returned first
*/
bool nullsFirst() const;
/**
* Set if NULLS should be returned first
*/
void setNullsFirst( bool nullsFirst );
/**
* Dumps the content to an SQL equivalent
*/
QString dump() const;
// friend inline int qHash(const OrderByClause &a) { return qHash(a.mExpression.expression()) ^ qHash(a.mAscending) ^ qHash( a.mNullsFirst); }
private:
QgsExpression mExpression;
bool mAscending;
bool mNullsFirst;
};
/**
* \ingroup core
* Represents a list of OrderByClauses, with the most important first and the least
* important last.
*
* \since QGIS 2.14
*/
class OrderBy : public QList<QgsFeatureRequest::OrderByClause>
{
public:
/**
* Create a new empty order by
*/
CORE_EXPORT OrderBy();
/**
* Create a new order by from a list of clauses
*/
CORE_EXPORT OrderBy( const QList<QgsFeatureRequest::OrderByClause> &other );
/**
* Gets a copy as a list of OrderByClauses
*
* This is only required in Python where the inheritance
* is not properly propagated and this makes it usable.
*/
QList<QgsFeatureRequest::OrderByClause> CORE_EXPORT list() const;
/**
* Serialize to XML
*/
void CORE_EXPORT save( QDomElement &elem ) const;
/**
* Deserialize from XML
*/
void CORE_EXPORT load( const QDomElement &elem );
/**
* Returns a set of used attributes
*/
QSet<QString> CORE_EXPORT usedAttributes() const;
/**
* Dumps the content to an SQL equivalent syntax
*/
QString CORE_EXPORT dump() const;
};
/**
* A special attribute that if set matches all attributes
*/
static const QString ALL_ATTRIBUTES;
//! construct a default request: for all features get attributes and geometries
QgsFeatureRequest();
//! construct a request with feature ID filter
explicit QgsFeatureRequest( QgsFeatureId fid );
//! construct a request with feature ID filter
explicit QgsFeatureRequest( const QgsFeatureIds &fids );
/**
* Construct a request with \a rectangle bounding box filter.
*
* When a destination CRS is set using setDestinationCrs(), \a rectangle
* is expected to be in the same CRS as the destinationCrs(). Otherwise, \a rectangle
* should use the same CRS as the source layer/provider.
*/
explicit QgsFeatureRequest( const QgsRectangle &rectangle );
//! construct a request with a filter expression
explicit QgsFeatureRequest( const QgsExpression &expr, const QgsExpressionContext &context = QgsExpressionContext() );
//! copy constructor
QgsFeatureRequest( const QgsFeatureRequest &rh );
//! Assignment operator
QgsFeatureRequest &operator=( const QgsFeatureRequest &rh );
/**
* Returns the filter type which is currently set on this request
*
* \returns Filter type
*/
FilterType filterType() const { return mFilter; }
/**
* Sets the \a rectangle from which features will be taken. An empty rectangle removes the filter.
*
* When a destination CRS is set using setDestinationCrs(), \a rectangle
* is expected to be in the same CRS as the destinationCrs(). Otherwise, \a rectangle
* should use the same CRS as the source layer/provider.
*
* \see filterRect()
*/
QgsFeatureRequest &setFilterRect( const QgsRectangle &rectangle );
/**
* Returns the rectangle from which features will be taken. If the returned
* rectangle is null, then no filter rectangle is set.
*
* When a destination CRS is set using setDestinationCrs(), the rectangle
* will be in the same CRS as the destinationCrs(). Otherwise, the rectangle
* will use the same CRS as the source layer/provider.
*
* \see setFilterRect()
*/
const QgsRectangle &filterRect() const { return mFilterRect; }
//! Sets feature ID that should be fetched.
QgsFeatureRequest &setFilterFid( QgsFeatureId fid );
//! Gets the feature ID that should be fetched.
QgsFeatureId filterFid() const { return mFilterFid; }
//! Sets feature IDs that should be fetched.
QgsFeatureRequest &setFilterFids( const QgsFeatureIds &fids );
//! Gets feature IDs that should be fetched.
const QgsFeatureIds &filterFids() const { return mFilterFids; }
/**
* Sets invalid geometry checking behavior.
* \note Invalid geometry checking is not performed when retrieving features
* directly from a QgsVectorDataProvider.
* \see invalidGeometryCheck()
* \since QGIS 3.0
*/
QgsFeatureRequest &setInvalidGeometryCheck( InvalidGeometryCheck check );
/**
* Returns the invalid geometry checking behavior.
* \see setInvalidGeometryCheck()
* \since QGIS 3.0
*/
InvalidGeometryCheck invalidGeometryCheck() const { return mInvalidGeometryFilter; }
/**
* Sets a callback function to use when encountering an invalid geometry and
* invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid. This function will be
* called using the feature with invalid geometry as a parameter.
* \see invalidGeometryCallback()
* \since QGIS 3.0
*/
#ifndef SIP_RUN
QgsFeatureRequest &setInvalidGeometryCallback( const std::function< void( const QgsFeature & )> &callback );
#else
QgsFeatureRequest &setInvalidGeometryCallback( SIP_PYCALLABLE / AllowNone / );
% MethodCode
Py_BEGIN_ALLOW_THREADS
sipCpp->setInvalidGeometryCallback( [a0]( const QgsFeature &arg )
{
SIP_BLOCK_THREADS
Py_XDECREF( sipCallMethod( NULL, a0, "D", &arg, sipType_QgsFeature, NULL ) );
SIP_UNBLOCK_THREADS
} );
sipRes = sipCpp;
Py_END_ALLOW_THREADS
% End
#endif
/**
* Returns the callback function to use when encountering an invalid geometry and
* invalidGeometryCheck() is set to GeometryAbortOnInvalid or GeometrySkipInvalid.
* \note not available in Python bindings
* \see setInvalidGeometryCallback()
* \since QGIS 3.0
*/
std::function< void( const QgsFeature & ) > invalidGeometryCallback() const { return mInvalidGeometryCallback; } SIP_SKIP
/**
* Set the filter expression. {\see QgsExpression}
* \param expression expression string
* \see filterExpression
* \see setExpressionContext
*/
QgsFeatureRequest &setFilterExpression( const QString &expression );
/**
* Returns the filter expression if set.
* \see setFilterExpression
* \see expressionContext
*/
QgsExpression *filterExpression() const { return mFilterExpression.get(); }
/**
* Modifies the existing filter expression to add an additional expression filter. The
* filter expressions are combined using AND, so only features matching both
* the existing expression and the additional expression will be returned.
* \since QGIS 2.14
*/
QgsFeatureRequest &combineFilterExpression( const QString &expression );
/**
* Returns the expression context used to evaluate filter expressions.
* \see setExpressionContext
* \see filterExpression
* \since QGIS 2.12
*/
QgsExpressionContext *expressionContext() { return &mExpressionContext; }
/**
* Sets the expression context used to evaluate filter expressions.
* \see expressionContext
* \see setFilterExpression
* \since QGIS 2.12
*/
QgsFeatureRequest &setExpressionContext( const QgsExpressionContext &context );
/**
* Disables filter conditions.
* The spatial filter (filterRect) will be kept in place.
*
* \returns The object the method is called on for chaining
*
* \since QGIS 2.12
*/
QgsFeatureRequest &disableFilter() { mFilter = FilterNone; mFilterExpression.reset(); return *this; }
/**
* Adds a new OrderByClause, appending it as the least important one.
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* If the order is ascending, by default nulls are last
* If the order is descending, by default nulls are first
*
* \since QGIS 2.14
*/
QgsFeatureRequest &addOrderBy( const QString &expression, bool ascending = true );
/**
* Adds a new OrderByClause, appending it as the least important one.
*
* \param expression The expression to use for ordering
* \param ascending If the order should be ascending (1,2,3) or descending (3,2,1)
* \param nullsfirst If true, NULLS are at the beginning, if false, NULLS are at the end
*
* \since QGIS 2.14
*/
QgsFeatureRequest &addOrderBy( const QString &expression, bool ascending, bool nullsfirst );
/**
* Returns a list of order by clauses specified for this feature request.
*
* \since QGIS 2.14
*/
OrderBy orderBy() const;
/**
* Set a list of order by clauses.
*
* \since QGIS 2.14
*/
QgsFeatureRequest &setOrderBy( const OrderBy &orderBy );
/**
* Set the maximum number of features to request.
* \param limit maximum number of features, or -1 to request all features.
* \see limit()
* \since QGIS 2.14
*/
QgsFeatureRequest &setLimit( long limit );
/**
* Returns the maximum number of features to request, or -1 if no limit set.
* \see setLimit
* \since QGIS 2.14
*/
long limit() const { return mLimit; }
//! Sets flags that affect how features will be fetched
QgsFeatureRequest &setFlags( QgsFeatureRequest::Flags flags );
const Flags &flags() const { return mFlags; }
/**
* Set a subset of attributes that will be fetched.
*
* An empty attributes list indicates that no attributes will be fetched.
* To revert a call to setSubsetOfAttributes and fetch all available attributes,
* the SubsetOfAttributes flag should be removed from the request.
*/
QgsFeatureRequest &setSubsetOfAttributes( const QgsAttributeList &attrs );
/**
* Returns the subset of attributes which at least need to be fetched
* \returns A list of attributes to be fetched
*/
QgsAttributeList subsetOfAttributes() const { return mAttrs; }
//! Sets a subset of attributes by names that will be fetched
QgsFeatureRequest &setSubsetOfAttributes( const QStringList &attrNames, const QgsFields &fields );
//! Sets a subset of attributes by names that will be fetched
QgsFeatureRequest &setSubsetOfAttributes( const QSet<QString> &attrNames, const QgsFields &fields );
/**
* Set a simplification method for geometries that will be fetched
* \since QGIS 2.2
*/
QgsFeatureRequest &setSimplifyMethod( const QgsSimplifyMethod &simplifyMethod );
/**
* Gets simplification method for geometries that will be fetched
* \since QGIS 2.2
*/
const QgsSimplifyMethod &simplifyMethod() const { return mSimplifyMethod; }
/**
* Returns the destination coordinate reference system for feature's geometries,
* or an invalid QgsCoordinateReferenceSystem if no reprojection will be done
* and all features will be left with their original geometry.
* \see setDestinationCrs()
* \see transformContext()
* \since QGIS 3.0
*/
QgsCoordinateReferenceSystem destinationCrs() const;
/**
* Returns the transform context, for use when a destinationCrs() has been set
* and reprojection is required
* \see setDestinationCrs()
* \see destinationCrs()
* \since QGIS 3.0
*/
QgsCoordinateTransformContext transformContext() const;
/**
* Sets the destination \a crs for feature's geometries. If set, all
* geometries will be reprojected from their original coordinate reference
* system to this desired reference system. If \a crs is an invalid
* QgsCoordinateReferenceSystem then no reprojection will be done
* and all features will be left with their original geometry.
*
* When a \a crs is set using setDestinationCrs(), then any filterRect()
* set on the request is expected to be in the same CRS as the destination
* CRS.
*
* The feature geometry transformation to the destination CRS is performed
* after all filter expressions are tested and any virtual fields are
* calculated. Accordingly, any geometric expressions used in
* filterExpression() will be performed in the original
* source CRS. This ensures consistent results are returned regardless of the
* destination CRS. Similarly, virtual field values will be calculated using the
* original geometry in the source CRS, so these values are not affected by
* any destination CRS transform present in the feature request.
*
* \see destinationCrs()
* \since QGIS 3.0
*/
QgsFeatureRequest &setDestinationCrs( const QgsCoordinateReferenceSystem &crs, const QgsCoordinateTransformContext &context );
/**
* Sets a callback function to use when encountering a transform error when iterating
* features and a destinationCrs() is set. This function will be
* called using the feature which encountered the transform error as a parameter.
* \see transformErrorCallback()
* \see setDestinationCrs()
* \since QGIS 3.0
*/
#ifndef SIP_RUN
QgsFeatureRequest &setTransformErrorCallback( const std::function< void( const QgsFeature & )> &callback );
#else
QgsFeatureRequest &setTransformErrorCallback( SIP_PYCALLABLE / AllowNone / );
% MethodCode
Py_BEGIN_ALLOW_THREADS
sipCpp->setTransformErrorCallback( [a0]( const QgsFeature &arg )
{
SIP_BLOCK_THREADS
Py_XDECREF( sipCallMethod( NULL, a0, "D", &arg, sipType_QgsFeature, NULL ) );
SIP_UNBLOCK_THREADS
} );
sipRes = sipCpp;
Py_END_ALLOW_THREADS
% End
#endif
/**
* Returns the callback function to use when encountering a transform error when iterating
* features and a destinationCrs() is set.
* \note not available in Python bindings
* \see setTransformErrorCallback()
* \see destinationCrs()
* \since QGIS 3.0
*/
std::function< void( const QgsFeature & ) > transformErrorCallback() const { return mTransformErrorCallback; } SIP_SKIP
/**
* Check if a feature is accepted by this requests filter
*
* \param feature The feature which will be tested
*
* \returns true, if the filter accepts the feature
*
* \since QGIS 2.1
*/
bool acceptFeature( const QgsFeature &feature );
/**
* Returns the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool
* at this moment. A negative value (which is set by default) will wait forever.
*
* \note Only works if the provider supports this option.
*
* \deprecated Use timeout() instead.
* \since QGIS 3.0
*/
Q_DECL_DEPRECATED int connectionTimeout() const SIP_DEPRECATED;
/**
* Sets the timeout (in milliseconds) for how long we should wait for a connection if none is available from the pool
* at this moment. A negative value (which is set by default) will wait forever.
*
* \note Only works if the provider supports this option.
*
* \deprecated Use setTimeout() instead.
* \since QGIS 3.0
*/
Q_DECL_DEPRECATED QgsFeatureRequest &setConnectionTimeout( int connectionTimeout ) SIP_DEPRECATED;
/**
* Returns the timeout (in milliseconds) for the maximum time we should wait during feature requests before a
* feature is returned. A negative value (which is set by default) will wait forever.
*
* \note Only works if the provider supports this option.
*
* \since QGIS 3.4
*/
int timeout() const;
/**
* Sets the \a timeout (in milliseconds) for the maximum time we should wait during feature requests before a
* feature is returned. A negative value (which is set by default) will wait forever.
*
* \note Only works if the provider supports this option.
*
* \since QGIS 3.4
*/
QgsFeatureRequest &setTimeout( int timeout );
/**
* In case this request may be run nested within another already running
* iteration on the same connection, set this to true.
*
* If this flag is true, this request will be able to make use of "spare"
* connections to avoid deadlocks.
*
* For example, this should be set on requests that are issued from an
* expression function.
*
* \since QGIS 3.4
*/
bool requestMayBeNested() const;
/**
* In case this request may be run nested within another already running
* iteration on the same connection, set this to true.
*
* If this flag is true, this request will be able to make use of "spare"
* connections to avoid deadlocks.
*
* For example, this should be set on requests that are issued from an
* expression function.
*
* \since QGIS 3.4
*/
QgsFeatureRequest &setRequestMayBeNested( bool requestMayBeNested );
protected:
FilterType mFilter = FilterNone;
QgsRectangle mFilterRect;
QgsFeatureId mFilterFid = -1;
QgsFeatureIds mFilterFids;
std::unique_ptr< QgsExpression > mFilterExpression;
QgsExpressionContext mExpressionContext;
Flags mFlags;
QgsAttributeList mAttrs;
QgsSimplifyMethod mSimplifyMethod;
long mLimit = -1;
OrderBy mOrderBy;
InvalidGeometryCheck mInvalidGeometryFilter = GeometryNoCheck;
std::function< void( const QgsFeature & ) > mInvalidGeometryCallback;
std::function< void( const QgsFeature & ) > mTransformErrorCallback;
QgsCoordinateReferenceSystem mCrs;
QgsCoordinateTransformContext mTransformContext;
int mTimeout = -1;
int mRequestMayBeNested = false;
};
Q_DECLARE_OPERATORS_FOR_FLAGS( QgsFeatureRequest::Flags )
class QgsFeatureIterator;
class QgsAbstractFeatureIterator;
/**
* \ingroup core
* Base class that can be used for any class that is capable of returning features
* \since QGIS 2.4
*/
class CORE_EXPORT QgsAbstractFeatureSource
{
public:
virtual ~QgsAbstractFeatureSource();
/**
* Gets an iterator for features matching the specified request
* \param request The request
* \returns A feature iterator
*/
virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest &request = QgsFeatureRequest() ) = 0;
protected:
void iteratorOpened( QgsAbstractFeatureIterator *it );
void iteratorClosed( QgsAbstractFeatureIterator *it );
QSet< QgsAbstractFeatureIterator * > mActiveIterators;
template<typename> friend class QgsAbstractFeatureIteratorFromSource;
};
#endif // QGSFEATUREREQUEST_H