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https://github.com/qgis/QGIS.git
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307aabd66a
This commit adds a number of different forms of aggregates to
the expression engine.
1. Aggregates within the current layer, eg sum("passengers")
Supports sub expressions (ie sum("passengers"/2) ), group by
( sum("passengers", group_by:="line_segment") ), and optional
filters ( sum("passengers", filter:= "station_class" > 3 ) )
2. Relational aggregates, which calculate an aggregate over
all matching child features from a relation, eg
relation_aggregate( 'my_relation', 'mean', "some_child_field" )
3. A summary aggregate function, for calculating aggregates
on other layers. Eg aggregate('rail_station_layer','sum',"passengers")
The summary aggregate function supports an optional filter,
making it possible to calculate things like:
aggregate('rail_stations','sum',"passengers",
intersects(@atlas_geometry, $geometry ) )
for calculating the total number of passengers for the stations
inside the current atlas feature
In all cases the calculations are cached inside the expression
context, so they only need to be calculated once for each
set of expression evaluations.
Sponsored by Kanton of Zug, Switzerland
385 lines
13 KiB
Plaintext
385 lines
13 KiB
Plaintext
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class QgsVectorDataProvider : QgsDataProvider
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{
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%TypeHeaderCode
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#include <qgsvectordataprovider.h>
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%End
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public:
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// If you add to this, please also add to capabilitiesString()
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/**
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* enumeration with capabilities that providers might implement
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*/
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enum Capability
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{
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/** Provider has no capabilities */
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NoCapabilities,
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/** Allows adding features */
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AddFeatures,
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/** Allows deletion of features */
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DeleteFeatures,
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/** Allows modification of attribute values */
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ChangeAttributeValues,
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/** Allows addition of new attributes (fields) */
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AddAttributes,
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/** Allows deletion of attributes (fields) */
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DeleteAttributes,
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/** DEPRECATED - do not use */
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SaveAsShapefile,
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/** Allows creation of spatial index */
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CreateSpatialIndex,
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/** Fast access to features using their ID */
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SelectAtId,
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/** Allows modifications of geometries */
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ChangeGeometries,
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/** DEPRECATED - do not use */
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SelectGeometryAtId,
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/** DEPRECATED - do not use */
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RandomSelectGeometryAtId,
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/** DEPRECATED - do not use */
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SequentialSelectGeometryAtId,
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/** DEPRECATED - do not use */
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CreateAttributeIndex,
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/** Allows user to select encoding */
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SelectEncoding,
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/** Supports simplification of geometries on provider side according to a distance tolerance */
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SimplifyGeometries,
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/** Supports topological simplification of geometries on provider side according to a distance tolerance */
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SimplifyGeometriesWithTopologicalValidation,
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/** Supports transactions*/
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TransactionSupport,
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/** Supports circular geometry types (circularstring, compoundcurve, curvepolygon)*/
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CircularGeometries,
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/** Supports joint updates for attributes and geometry
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* Providers supporting this should still define ChangeGeometries | ChangeAttributeValues
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*/
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ChangeFeatures
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};
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/** Bitmask of all provider's editing capabilities */
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static const int EditingCapabilities;
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/**
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* Constructor of the vector provider
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* @param uri uniform resource locator (URI) for a dataset
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*/
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QgsVectorDataProvider( const QString& uri = QString() );
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/**
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* Destructor
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*/
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virtual ~QgsVectorDataProvider();
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/**
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* Return feature source object that can be used for querying provider's data. The returned feature source
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* is independent from provider - any changes to provider's state (e.g. change of subset string) will not be
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* reflected in the feature source, therefore it can be safely used for processing in background without
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* having to care about possible changes within provider that may happen concurrently. Also, even in the case
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* of provider being deleted, any feature source obtained from the provider will be kept alive and working
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* (they are independent and owned by the caller).
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*
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* Sometimes there are cases when some data needs to be shared between vector data provider and its feature source.
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* In such cases, the implementation must ensure that the data is not susceptible to run condition. For example,
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* if it is possible that both feature source and provider may need reading/writing to some shared data at the
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* same time, some synchronization mechanisms must be used (e.g. mutexes) to prevent data corruption.
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*
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* @note added in 2.4
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* @return new instance of QgsAbstractFeatureSource (caller is responsible for deleting it)
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*/
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virtual QgsAbstractFeatureSource* featureSource() const /Factory/;
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/**
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* Returns the permanent storage type for this layer as a friendly name.
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*/
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virtual QString storageType() const;
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/**
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* Query the provider for features specified in request.
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*/
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virtual QgsFeatureIterator getFeatures( const QgsFeatureRequest& request = QgsFeatureRequest() ) = 0;
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/**
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* Get feature type.
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* @return int representing the feature type
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*/
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virtual QGis::WkbType geometryType() const = 0;
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/**
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* Number of features in the layer
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* @return long containing number of features
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*/
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virtual long featureCount() const = 0;
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/**
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* Return a map of indexes with field names for this layer
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* @return map of fields
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* @see QgsFields
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*/
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virtual const QgsFields &fields() const = 0;
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/**
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* Return a short comment for the data that this provider is
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* providing access to (e.g. the comment for postgres table).
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*/
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virtual QString dataComment() const;
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/**
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* Returns the minimum value of an attribute
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* @param index the index of the attribute
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*
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* Default implementation walks all numeric attributes and caches minimal
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* and maximal values. If provider has facilities to retrieve minimal
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* value directly, override this function.
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*/
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virtual QVariant minimumValue( int index );
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/**
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* Returns the maximum value of an attribute
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* @param index the index of the attribute
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*
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* Default implementation walks all numeric attributes and caches minimal
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* and maximal values. If provider has facilities to retrieve maximal
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* value directly, override this function.
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*/
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virtual QVariant maximumValue( int index );
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/**
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* Return unique values of an attribute
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* @param index the index of the attribute
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* @param uniqueValues values reference to the list to fill
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* @param limit maxmum number of the values to return
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*
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* Default implementation simply iterates the features
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*/
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virtual void uniqueValues( int index, QList<QVariant> &uniqueValues /Out/, int limit = -1 );
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/** Calculates an aggregated value from the layer's features. The base implementation does nothing,
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* but subclasses can override this method to handoff calculation of aggregates to the provider.
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* @param aggregate aggregate to calculate
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* @param index the index of the attribute to calculate aggregate over
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* @param parameters parameters controlling aggregate calculation
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* @param context expression context for filter
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* @param ok will be set to true if calculation was successfully performed by the data provider
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* @return calculated aggregate value
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* @note added in QGIS 2.16
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*/
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virtual QVariant aggregate( QgsAggregateCalculator::Aggregate aggregate,
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int index,
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const QgsAggregateCalculator::AggregateParameters& parameters,
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QgsExpressionContext* context,
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bool& ok );
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/**
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* Returns the possible enum values of an attribute. Returns an empty stringlist if a provider does not support enum types
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* or if the given attribute is not an enum type.
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* @param index the index of the attribute
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* @param enumList reference to the list to fill
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*/
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virtual void enumValues( int index, QStringList& enumList /Out/ );
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/**
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* Adds a list of features
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* @return true in case of success and false in case of failure
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*/
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virtual bool addFeatures( QList<QgsFeature> &flist /In,Out/ );
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/**
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* Deletes one or more features
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* @param id list containing feature ids to delete
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* @return true in case of success and false in case of failure
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*/
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virtual bool deleteFeatures( const QSet<qint64> &id );
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/**
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* Adds new attributes
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* @param attributes list of new attributes
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* @return true in case of success and false in case of failure
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*/
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virtual bool addAttributes( const QList<QgsField> &attributes );
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/**
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* Deletes existing attributes
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* @param attributes a set containing indices of attributes
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* @return true in case of success and false in case of failure
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*/
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virtual bool deleteAttributes( const QSet<int> &attributes );
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/**
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* Changes attribute values of existing features.
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* @param attr_map a map containing changed attributes
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* @return true in case of success and false in case of failure
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*/
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virtual bool changeAttributeValues( const QMap<qint64, QMap<int, QVariant> > &attr_map );
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/**
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* Changes attribute values and geometries of existing features.
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* @param attr_map a map containing changed attributes
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* @param geometry_map A QgsGeometryMap whose index contains the feature IDs
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* that will have their geometries changed.
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* The second map parameter being the new geometries themselves
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* @return true in case of success and false in case of failure
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*/
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virtual bool changeFeatures( const QMap<qint64, QMap<int, QVariant> > &attr_map,
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const QMap<qint64, QgsGeometry> &geometry_map );
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/**
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* Returns the default value for field specified by @c fieldId
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*/
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virtual QVariant defaultValue( int fieldId );
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/**
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* Changes geometries of existing features
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* @param geometry_map A QgsGeometryMap whose index contains the feature IDs
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* that will have their geometries changed.
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* The second map parameter being the new geometries themselves
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* @return True in case of success and false in case of failure
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*/
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virtual bool changeGeometryValues( const QMap<qint64, QgsGeometry> &geometry_map );
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/**
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* Creates a spatial index on the datasource (if supported by the provider type).
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* @return true in case of success
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*/
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virtual bool createSpatialIndex();
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/** Create an attribute index on the datasource*/
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virtual bool createAttributeIndex( int field );
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/** Returns a bitmask containing the supported capabilities
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Note, some capabilities may change depending on whether
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a spatial filter is active on this provider, so it may
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be prudent to check this value per intended operation.
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*/
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virtual int capabilities() const;
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/**
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* Returns the above in friendly format.
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*/
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QString capabilitiesString() const;
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/**
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* Set encoding used for accessing data from layer
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*/
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virtual void setEncoding( const QString& e );
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/**
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* Get encoding which is used for accessing data
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*/
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QString encoding() const;
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/**
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* Returns the index of a field name or -1 if the field does not exist
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*/
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int fieldNameIndex( const QString& fieldName ) const;
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/**
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* Return a map where the key is the name of the field and the value is its index
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*/
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QMap<QString, int> fieldNameMap() const;
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/**
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* Return list of indexes to fetch all attributes in nextFeature()
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*/
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QList<int> attributeIndexes();
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/**
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* Return list of indexes of fields that make up the primary key
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*/
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virtual QList<int> pkAttributeIndexes();
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/**
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* Return list of indexes to names for QgsPalLabeling fix
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*/
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virtual QHash<int, QString> palAttributeIndexNames() const;
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/**
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* check if provider supports type of field
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*/
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bool supportedType( const QgsField &field ) const;
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struct NativeType
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{
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NativeType( const QString& typeDesc, const QString& typeName, QVariant::Type type, int minLen = 0, int maxLen = 0, int minPrec = 0, int maxPrec = 0 );
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QString mTypeDesc;
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QString mTypeName;
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QVariant::Type mType;
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int mMinLen;
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int mMaxLen;
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int mMinPrec;
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int mMaxPrec;
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};
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/**
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* Returns the names of the supported types
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*/
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const QList< QgsVectorDataProvider::NativeType > &nativeTypes() const;
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/**
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* Returns true if the provider is strict about the type of inserted features
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* (e.g. no multipolygon in a polygon layer)
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*/
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bool doesStrictFeatureTypeCheck() const;
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/** Returns a list of available encodings */
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static const QStringList &availableEncodings();
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/**
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* Provider has errors to report
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*/
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bool hasErrors();
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/**
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* Clear recorded errors
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*/
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void clearErrors();
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/**
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* Get recorded errors
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*/
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QStringList errors();
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/**
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* It returns false by default.
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* Must be implemented by providers that support saving and loading styles to db returning true
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*/
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virtual bool isSaveAndLoadStyleToDBSupported();
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static QVariant convertValue( QVariant::Type type, const QString& value );
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/**
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* Returns the transaction this data provider is included in, if any.
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*/
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virtual QgsTransaction* transaction() const;
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/**
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* Forces a reload of the underlying datasource if the provider implements this
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* method.
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* In particular on the OGR provider, a pooled connection will be invalidated.
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* This forces QGIS to reopen a file or connection.
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* This can be required if the underlying file is replaced.
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*/
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virtual void forceReload();
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/**
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* Get the list of layer ids on which this layer depends. This in particular determines the order of layer loading.
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*/
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virtual QSet<QString> layerDependencies() const;
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signals:
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/** Signals an error in this provider */
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void raiseError( const QString& msg );
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protected:
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void clearMinMaxCache();
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void fillMinMaxCache();
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void pushError( const QString& msg );
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/** Converts the geometry to the provider type if possible / necessary
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@return the converted geometry or nullptr if no conversion was necessary or possible*/
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QgsGeometry* convertToProviderType( const QgsGeometry* geom ) const /Factory/;
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};
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