Add auto-discovery of relations for PostgresQL

Fixed the add relation functionnality: the table is sorted. When the code
was setting the sorted column, the row was sorted and the other columns it was
setting were set on the wrong row.

Author: Patrick Valsecchi

python/core/qgsrelation.sip

@@ -171,6 +171,12 @@ class QgsRelation
      */
     QString id() const;
 
+    /**
+     * Generate a (project-wide) unique id for this relation
+     * @note added in QGIS 3.0
+     */
+    void generateId();
+
     /**
      * Access the referencing (child) layer's id
      * This is the layer which has the field(s) which point to another layer
@@ -241,6 +247,15 @@ class QgsRelation
      */
     bool isValid() const;
 
+    /**
+     * Compares the two QgsRelation, ignoring the name and the ID.
+     *
+     * @param other The other relation
+     * @return true if they are similar
+     * @note added in QGIS 3.0
+     */
+    bool hasEqualDefinition( const QgsRelation& other ) const;
+
   protected:
     /**
      * Updates the validity status of this relation.

python/core/qgsrelationmanager.sip

@@ -90,6 +90,16 @@ class QgsRelationManager : QObject
      */
     QList<QgsRelation> referencedRelations( QgsVectorLayer *layer = 0 ) const;
 
+    /**
+     * Discover all the relations available from the current layers.
+     *
+     * @param existingRelations the existing relations to filter them out
+     * @param layers the current layers
+     * @return the list of discovered relations
+     * @note added in QGIS 3.0
+     */
+    static QList<QgsRelation> discoverRelations( const QList<QgsRelation>& existingRelations, const QList<QgsVectorLayer*>& layers );
+
   signals:
     /** This signal is emitted when the relations were loaded after reading a project */
     void relationsLoaded();

python/core/qgsvectordataprovider.sip

@@ -371,6 +371,15 @@ class QgsVectorDataProvider : QgsDataProvider
      */
     virtual QSet<QgsMapLayerDependency> dependencies() const;
 
+    /**
+     * Discover the available relations with the given layers.
+     * @param self the layer using this data provider.
+     * @param layers the other layers.
+     * @return the list of N-1 relations from this provider.
+     * @note added in QGIS 3.0
+     */
+    virtual QList<QgsRelation> discoverRelations( const QgsVectorLayer* self, const QList<QgsVectorLayer*>& layers ) const;
+
   signals:
     /** Signals an error in this provider */
     void raiseError( const QString& msg );

src/app/CMakeLists.txt

@@ -28,6 +28,7 @@ SET(QGIS_APP_SRCS
   qgsdecorationscalebardialog.cpp
   qgsdecorationgrid.cpp
   qgsdecorationgriddialog.cpp
+  qgsdiscoverrelationsdlg.cpp
   qgsdxfexportdialog.cpp
   qgsformannotationdialog.cpp
   qgsguivectorlayertools.cpp
@@ -207,6 +208,7 @@ SET (QGIS_APP_MOC_HDRS
   qgsdecorationgriddialog.h
   qgsdelattrdialog.h
   qgsdiagramproperties.h
+  qgsdiscoverrelationsdlg.h
   qgsdisplayangle.h
   qgsdxfexportdialog.h
   qgsfeatureaction.h

src/app/qgsdiscoverrelationsdlg.cpp

@@ -0,0 +1,61 @@
+/***************************************************************************
+    qgsdiscoverrelationsdlg.cpp
+    ---------------------
+    begin                : September 2016
+    copyright            : (C) 2016 by Patrick Valsecchi
+    email                : patrick dot valsecchi at camptocamp 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.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#include "qgsdiscoverrelationsdlg.h"
+#include "qgsvectorlayer.h"
+#include "qgsrelationmanager.h"
+
+#include <QPushButton>
+
+QgsDiscoverRelationsDlg::QgsDiscoverRelationsDlg( const QList<QgsRelation>& existingRelations, const QList<QgsVectorLayer*>& layers, QWidget *parent )
+    : QDialog( parent )
+    , mLayers( layers )
+{
+  setupUi( this );
+
+  mButtonBox->button( QDialogButtonBox::Ok )->setEnabled( false );
+  connect( mRelationsTable->selectionModel(), &QItemSelectionModel::selectionChanged, this, &QgsDiscoverRelationsDlg::onSelectionChanged );
+
+  mFoundRelations = QgsRelationManager::discoverRelations( existingRelations, layers );
+  Q_FOREACH ( const QgsRelation& relation, mFoundRelations ) addRelation( relation );
+
+  mRelationsTable->resizeColumnsToContents();
+
+}
+
+void QgsDiscoverRelationsDlg::addRelation( const QgsRelation &rel )
+{
+  const int row = mRelationsTable->rowCount();
+  mRelationsTable->insertRow( row );
+  mRelationsTable->setItem( row, 0, new QTableWidgetItem( rel.name() ) );
+  mRelationsTable->setItem( row, 1, new QTableWidgetItem( rel.referencingLayer()->name() ) );
+  mRelationsTable->setItem( row, 2, new QTableWidgetItem( rel.fieldPairs().at( 0 ).referencingField() ) );
+  mRelationsTable->setItem( row, 3, new QTableWidgetItem( rel.referencedLayer()->name() ) );
+  mRelationsTable->setItem( row, 4, new QTableWidgetItem( rel.fieldPairs().at( 0 ).referencedField() ) );
+}
+
+QList<QgsRelation> QgsDiscoverRelationsDlg::relations() const
+{
+  QList<QgsRelation> result;
+  Q_FOREACH ( const QModelIndex& row, mRelationsTable->selectionModel()->selectedRows() )
+  {
+    result.append( mFoundRelations.at( row.row() ) );
+  }
+  return result;
+}
+
+void QgsDiscoverRelationsDlg::onSelectionChanged()
+{
+  mButtonBox->button( QDialogButtonBox::Ok )->setEnabled( mRelationsTable->selectionModel()->hasSelection() );
+}

src/app/qgsdiscoverrelationsdlg.h

@@ -0,0 +1,53 @@
+/***************************************************************************
+    qgsdiscoverrelationsdlg.h
+    ---------------------
+    begin                : September 2016
+    copyright            : (C) 2016 by Patrick Valsecchi
+    email                : patrick dot valsecchi at camptocamp 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 QGSDISCOVERRELATIONSDLG_H
+#define QGSDISCOVERRELATIONSDLG_H
+
+#include <QDialog>
+#include "ui_qgsdiscoverrelationsdlgbase.h"
+#include "qgsrelation.h"
+
+class QgsRelationManager;
+class QgsVectorLayer;
+
+/**
+ * Shows the list of relations discovered from the providers.
+ *
+ * The user can select some of them to add them to his project.
+ */
+class APP_EXPORT QgsDiscoverRelationsDlg : public QDialog, private Ui::QgsDiscoverRelationsDlgBase
+{
+    Q_OBJECT
+
+  public:
+    explicit QgsDiscoverRelationsDlg( const QList<QgsRelation>& existingRelations, const QList<QgsVectorLayer*>& layers, QWidget *parent = nullptr );
+
+    /**
+     * Get the selected relations.
+     */
+    QList<QgsRelation> relations() const;
+
+  private slots:
+    void onSelectionChanged();
+
+  private:
+    QList<QgsVectorLayer*> mLayers;
+    QList<QgsRelation> mFoundRelations;
+
+    void addRelation( const QgsRelation &rel );
+
+};
+
+#endif // QGSDISCOVERRELATIONSDLG_H

src/app/qgsrelationmanagerdialog.cpp

@@ -13,6 +13,7 @@
  *                                                                         *
  ***************************************************************************/
 
+#include "qgsdiscoverrelationsdlg.h"
 #include "qgsrelationadddlg.h"
 #include "qgsrelationmanagerdialog.h"
 #include "qgsrelationmanager.h"
@@ -46,6 +47,7 @@ void QgsRelationManagerDialog::setLayers( const QList< QgsVectorLayer* >& layers
 
 void QgsRelationManagerDialog::addRelation( const QgsRelation &rel )
 {
+  mRelationsTable->setSortingEnabled( false );
   int row = mRelationsTable->rowCount();
   mRelationsTable->insertRow( row );
 
@@ -54,7 +56,6 @@ void QgsRelationManagerDialog::addRelation( const QgsRelation &rel )
   item->setData( Qt::UserRole, QVariant::fromValue<QgsRelation>( rel ) );
   mRelationsTable->setItem( row, 0, item );
 
-
   item = new QTableWidgetItem( rel.referencingLayer()->name() );
   item->setFlags( Qt::ItemIsEditable );
   mRelationsTable->setItem( row, 1, item );
@@ -74,6 +75,7 @@ void QgsRelationManagerDialog::addRelation( const QgsRelation &rel )
   item = new QTableWidgetItem( rel.id() );
   item->setFlags( Qt::ItemIsEditable );
   mRelationsTable->setItem( row, 5, item );
+  mRelationsTable->setSortingEnabled( true );
 }
 
 void QgsRelationManagerDialog::on_mBtnAddRelation_clicked()
@@ -118,6 +120,18 @@ void QgsRelationManagerDialog::on_mBtnAddRelation_clicked()
   }
 }
 
+void QgsRelationManagerDialog::on_mBtnDiscoverRelations_clicked()
+{
+  QgsDiscoverRelationsDlg discoverDlg( relations(), mLayers, this );
+  if ( discoverDlg.exec() )
+  {
+    Q_FOREACH ( const QgsRelation& relation, discoverDlg.relations() )
+    {
+      addRelation( relation );
+    }
+  }
+}
+
 void QgsRelationManagerDialog::on_mBtnRemoveRelation_clicked()
 {
   if ( mRelationsTable->currentIndex().isValid() )

src/app/qgsrelationmanagerdialog.h

@@ -39,6 +39,7 @@ class APP_EXPORT QgsRelationManagerDialog : public QWidget, private Ui::QgsRelat
 
   public slots:
     void on_mBtnAddRelation_clicked();
+    void on_mBtnDiscoverRelations_clicked();
     void on_mBtnRemoveRelation_clicked();
 
   private:

src/core/qgsrelation.cpp

@@ -248,6 +248,16 @@ QString QgsRelation::id() const
   return mRelationId;
 }
 
+void QgsRelation::generateId()
+{
+  mRelationId = QString( "%1_%2_%3_%4" )
+                .arg( referencingLayerId(),
+                      mFieldPairs.at( 0 ).referencingField(),
+                      referencedLayerId(),
+                      mFieldPairs.at( 0 ).referencedField() );
+  updateRelationStatus();
+}
+
 QString QgsRelation::referencingLayerId() const
 {
   return mReferencingLayerId;
@@ -301,6 +311,11 @@ bool QgsRelation::isValid() const
   return mValid;
 }
 
+bool QgsRelation::hasEqualDefinition( const QgsRelation& other ) const
+{
+  return mReferencedLayerId == other.mReferencedLayerId && mReferencingLayerId == other.mReferencingLayerId && mFieldPairs == other.mFieldPairs;
+}
+
 void QgsRelation::updateRelationStatus()
 {
   const QMap<QString, QgsMapLayer*>& mapLayers = QgsMapLayerRegistry::instance()->mapLayers();

src/core/qgsrelation.h

@@ -57,6 +57,8 @@ class CORE_EXPORT QgsRelation
         QString referencingField() const { return first; }
         //! Get the name of the referenced (parent) field
         QString referencedField() const { return second; }
+
+        bool operator==( const FieldPair& other ) const { return first == other.first && second == other.second; }
     };
 
     /**
@@ -210,6 +212,12 @@ class CORE_EXPORT QgsRelation
      */
     QString id() const;
 
+    /**
+     * Generate a (project-wide) unique id for this relation
+     * @note added in QGIS 3.0
+     */
+    void generateId();
+
     /**
      * Access the referencing (child) layer's id
      * This is the layer which has the field(s) which point to another layer
@@ -272,6 +280,15 @@ class CORE_EXPORT QgsRelation
      */
     bool isValid() const;
 
+    /**
+     * Compares the two QgsRelation, ignoring the name and the ID.
+     *
+     * @param other The other relation
+     * @return true if they are similar
+     * @note added in QGIS 3.0
+     */
+    bool hasEqualDefinition( const QgsRelation& other ) const;
+
   protected:
     /**
      * Updates the validity status of this relation.