qgsvirtuallayerprovider.h

/***************************************************************************
           qgsvirtuallayerprovider.cpp Virtual layer data provider
begin                : Jan, 2015
copyright            : (C) 2015 Hugo Mercier, Oslandia
email                : hugo dot mercier at oslandia 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 QGSVIRTUAL_LAYER_PROVIDER_H
#define QGSVIRTUAL_LAYER_PROVIDER_H

#include <QTemporaryFile>

#include <qgsvectordataprovider.h>

#include "qgsconfig.h"
#include "qgscoordinatereferencesystem.h"
#include "qgsvirtuallayerdefinition.h"

#include "sqlite_helper.h"

class QgsVirtualLayerFeatureIterator;

class QgsVirtualLayerProvider: public QgsVectorDataProvider
{
    Q_OBJECT public:

    /**
     * Constructor of the vector provider
     * @param uri  uniform resource locator (URI) for a dataset
     */
    QgsVirtualLayerProvider( QString const &uri = "" );

    //! Destructor
    virtual ~ QgsVirtualLayerProvider();

    virtual QgsAbstractFeatureSource* featureSource() const override;

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

    /*! Get the QgsCoordinateReferenceSystem for this layer
     * @note Must be reimplemented by each provider.
     * If the provider isn't capable of returning
     * its projection an empty srs will be return, ti will return 0
     */
    virtual QgsCoordinateReferenceSystem crs() override;

    virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest& request ) override;

    /** Accessor for sql where clause used to limit dataset */
    virtual QString subsetString() override;

    /** mutator for sql where clause used to limit dataset size */
#if VERSION_INT < 21100
    virtual bool setSubsetString( QString theSQL, bool updateFeatureCount = true ) override;
#endif

    virtual bool supportsSubsetString() override { return true; }

    /** Get the feature type. This corresponds to
     * WKBPoint,
     * WKBLineString,
     * WKBPolygon,
     * WKBMultiPoint,
     * WKBMultiLineString or
     * WKBMultiPolygon
     * as defined in qgis.h
     */
    QGis::WkbType geometryType() const override;

    /** return the number of layers for the current data source
     */
    size_t layerCount() const;

    /**
     * Get the number of features in the layer
     */
    long featureCount() const override;

    /** Return the extent for this data layer
    */
    virtual QgsRectangle extent() override;

    /** Update the extent for this data layer
    */
    virtual void updateExtents() override;

    /**
      * Get the field information for the layer
      * @return vector of QgsField objects
      */
    const QgsFields & fields() const override;

    /** Returns the minimum value of an attribute
     *  @param index the index of the attribute */
    QVariant minimumValue( int index ) override;

    /** Returns the maximum value of an attribute
     *  @param index the index of the attribute */
    QVariant maximumValue( int index ) override;

    /** Return the unique values of an attribute
     *  @param index the index of the attribute
     *  @param values reference to the list of unique values
     *  @param limit maximum number of values */
    virtual void uniqueValues( int index, QList < QVariant > &uniqueValues, int limit = -1 ) override;

    /**Returns true if layer is valid
    */
    bool isValid() override;

    /**Describes if provider has save and load style support
       @return true in case saving style to db is supported by this provider*/
    virtual bool isSaveAndLoadStyleToDBSupported() override { return false; }

    /**Returns a bitmask containing the supported capabilities*/
    int capabilities() const override;

    bool supportsNativeTransform()
    {
      return false;
    }

    /** return the provider name
    */
    QString name() const override;

    /** return description
    */
    QString description() const override;

    /**
     * Return list of indexes of fields that make up the primary key
     */
    QgsAttributeList pkAttributeIndexes() override;

 private:

    // file on disk
    QString mPath;

    QgsScopedSqlite mSqlite;

    // underlying vector layers
    struct SourceLayer
    {
        SourceLayer(): layer(0) {}
        SourceLayer( QgsVectorLayer *l, const QString& n = "" ) : layer(l), name(n) {}
        SourceLayer( const QString& p, const QString& s, const QString& n, const QString& e = "UTF-8" ) :
            layer(0), name(n), source(s), provider(p), encoding(e) {}
        // non-null if it refers to a live layer
        QgsVectorLayer* layer;
        QString name;
        // non-empty if it is an embedded layer
        QString source;
        QString provider;
        QString encoding;
    };
    struct SourceLayers : public QVector<SourceLayer>
    {
        SourceLayers() : QVector<SourceLayer>() {}
    };
    SourceLayers mLayers;

    bool mValid;

    // temporary file used for temporary virtual layer
    QScopedPointer<QTemporaryFile> mTempFile;

    QString mTableName;

    QgsFields mFields;

    QgsCoordinateReferenceSystem mCrs;

    // nonce used for temporary file
    static int mNonce;

    QgsVirtualLayerDefinition mDefinition;

    QString mSubset;

    void resetSqlite();

    mutable bool mCachedStatistics;
    mutable qint64 mFeatureCount;
    mutable QgsRectangle mExtent;

    void updateStatistics() const;

    bool openIt();
    bool createIt();
    bool loadSourceLayers();

    friend class QgsVirtualLayerFeatureIterator;

private slots:
    void onLayerDeleted();
};

#endif