Class: QgsVectorLayerCache

Caches features for a given QgsVectorLayer.

The cached features can be indexed by QgsAbstractCacheIndex.

Proper indexing for a given use-case may speed up performance substantially.

Class Hierarchy

Base classes

QObject

class qgis.core.QgsVectorLayerCache

Bases: QObject

addCacheIndex(self, cacheIndex: QgsAbstractCacheIndex | None)

Adds a QgsAbstractCacheIndex to this cache. Cache indices know about features present in this cache and decide, if enough information is present in the cache to respond to a QgsFeatureRequest. The layer cache will take ownership of the index.

Parameters:

cacheIndex (Optional[QgsAbstractCacheIndex]) – The cache index to add.

signal attributeValueChanged

pyqtSignal(*types, name: str = …, revision: int = …, arguments: Sequence = …) -> PYQT_SIGNAL

types is normally a sequence of individual types. Each type is either a type object or a string that is the name of a C++ type. Alternatively each type could itself be a sequence of types each describing a different overloaded signal. name is the optional C++ name of the signal. If it is not specified then the name of the class attribute that is bound to the signal is used. revision is the optional revision of the signal that is exported to QML. If it is not specified then 0 is used. arguments is the optional sequence of the names of the signal’s arguments.

cacheGeometry(self) → bool

Returns True if the cache will fetch and cache feature geometries.

See also

setCacheGeometry()

Return type:

bool

cacheSize(self) → int

Returns the maximum number of features this cache will hold. In case full caching is enabled, this number can change, as new features get added.

Return type:

int

Returns:

int

cacheSubsetOfAttributes(self) → List[int]

Returns the list (possibly a subset) of cached attributes.

Note

By default the cache will store all layer’s attributes.

See also

setCacheSubsetOfAttributes()

Added in version 3.32.

Return type:

List[int]

cachedFeatureIds(self) → Any

Returns the set of feature IDs for features which are cached.

See also

isFidCached()

Return type:

Any

signal cachedLayerDeleted

pyqtSignal(*types, name: str = …, revision: int = …, arguments: Sequence = …) -> PYQT_SIGNAL

types is normally a sequence of individual types. Each type is either a type object or a string that is the name of a C++ type. Alternatively each type could itself be a sequence of types each describing a different overloaded signal. name is the optional C++ name of the signal. If it is not specified then the name of the class attribute that is bound to the signal is used. revision is the optional revision of the signal that is exported to QML. If it is not specified then 0 is used. arguments is the optional sequence of the names of the signal’s arguments.

checkInformationCovered(self, featureRequest: QgsFeatureRequest) → bool

Checks if the information required to complete the request is cached. i.e. If all attributes required and the geometry is held in the cache. Please note, that this does not check, if the requested features are cached.

Parameters:

featureRequest (QgsFeatureRequest) – The QgsFeatureRequest to be answered

Return type:

bool

Returns:

True if the information is being cached, False if not

completeFeatureAtId(self, featureId: int, skipCache: bool = False)

Gets the feature at the given feature id with all attributes and geometry, if the cached feature already contains all attributes and geometry, calling this function has the same effect as calling featureAtId().

Considers the changed, added, deleted and permanent features

Parameters:

• featureId (int) – The id of the feature to query

• skipCache (bool = False) -> (bool) – Will query the layer regardless if the feature is in the cache already

Returns:

• True in case of success

• feature: The result of the operation will be written to this feature

See also

featureAtId()

Added in version 3.44.

signal featureAdded

pyqtSignal(*types, name: str = …, revision: int = …, arguments: Sequence = …) -> PYQT_SIGNAL

types is normally a sequence of individual types. Each type is either a type object or a string that is the name of a C++ type. Alternatively each type could itself be a sequence of types each describing a different overloaded signal. name is the optional C++ name of the signal. If it is not specified then the name of the class attribute that is bound to the signal is used. revision is the optional revision of the signal that is exported to QML. If it is not specified then 0 is used. arguments is the optional sequence of the names of the signal’s arguments.

featureAtId(self, featureId: int, skipCache: bool = False)

Gets the feature at the given feature id. Considers the changed, added, deleted and permanent features

Parameters:

• featureId (int) – The id of the feature to query

• skipCache (bool = False) -> (bool) – Will query the layer regardless if the feature is in the cache already

Returns:

• True in case of success

• feature: The result of the operation will be written to this feature

featureAtIdWithAllAttributes(self, featureId: int, skipCache: bool = False)

Gets the feature at the given feature id with all attributes, if the cached feature already contains all attributes, calling this function has the same effect as calling featureAtId().

Considers the changed, added, deleted and permanent features

Parameters:

• featureId (int) – The id of the feature to query

• skipCache (bool = False) -> (bool) – Will query the layer regardless if the feature is in the cache already

Returns:

• True in case of success

• feature: The result of the operation will be written to this feature

See also

featureAtId()

Added in version 3.32.

featureCount(self) → int

Returns the number of features contained in the source, or -1 if the feature count is unknown.

Return type:

int

featureRemoved(self, fid: int)

Gets called, whenever a feature has been removed. Broadcasts this information to indices, so they can invalidate their cache if required.

Parameters:

fid (int) – The feature id of the removed feature.

fields(self) → QgsFields

Returns the fields associated with features in the cache.

Return type:

QgsFields

signal finished

pyqtSignal(*types, name: str = …, revision: int = …, arguments: Sequence = …) -> PYQT_SIGNAL

types is normally a sequence of individual types. Each type is either a type object or a string that is the name of a C++ type. Alternatively each type could itself be a sequence of types each describing a different overloaded signal. name is the optional C++ name of the signal. If it is not specified then the name of the class attribute that is bound to the signal is used. revision is the optional revision of the signal that is exported to QML. If it is not specified then 0 is used. arguments is the optional sequence of the names of the signal’s arguments.

getFeature(self, fid: int) → QgsFeature

Query the layer for the feature with the given id. If there is no such feature, the returned feature will be invalid.

Parameters:

fid (int)

Return type:

QgsFeature

getFeatures(self, featureRequest: QgsFeatureRequest = QgsFeatureRequest()) → QgsFeatureIterator

Query this VectorLayerCache for features. If the VectorLayerCache (and moreover any of its indices) is able to satisfy the request, the returned QgsFeatureIterator will iterate over cached features. If it’s not possible to fully satisfy the request from the cache, part or all of the features will be requested from the data provider.

Parameters:

featureRequest (QgsFeatureRequest = QgsFeatureRequest()) – The request specifying filter and required data.

Return type:

QgsFeatureIterator

Returns:

An iterator over the requested data.

getFeatures(self, expression: Optional[str]) -> QgsFeatureIterator Query the layer for features matching a given expression.

getFeatures(self, fids: Any) -> QgsFeatureIterator Query the layer for the features with the given ids.

getFeatures(self, rectangle: QgsRectangle) -> QgsFeatureIterator Query the layer for the features which intersect the specified rectangle.

hasFullCache(self) → bool

Returns True if the cache is complete, ie it contains all features. This may happen as a result of a call to setFullCache() or by through a feature request which resulted in all available features being cached.

See also

setFullCache()

Return type:

bool

signal invalidated

pyqtSignal(*types, name: str = …, revision: int = …, arguments: Sequence = …) -> PYQT_SIGNAL

types is normally a sequence of individual types. Each type is either a type object or a string that is the name of a C++ type. Alternatively each type could itself be a sequence of types each describing a different overloaded signal. name is the optional C++ name of the signal. If it is not specified then the name of the class attribute that is bound to the signal is used. revision is the optional revision of the signal that is exported to QML. If it is not specified then 0 is used. arguments is the optional sequence of the names of the signal’s arguments.

isFidCached(self, fid: int) → bool

Check if a certain feature id is cached.

Parameters:

fid (int) – The feature id to look for

Return type:

bool

Returns:

True if this id is in the cache

See also

cachedFeatureIds()

layer(self) → QgsVectorLayer | None

Returns the layer to which this cache belongs

Return type:

Optional[QgsVectorLayer]

removeCachedFeature(self, fid: int) → bool

Removes the feature identified by fid from the cache if present.

Parameters:

fid (int) – The id of the feature to delete

Return type:

bool

Returns:

True if the feature was removed, False if the feature id was not found in the cache

requestCompleted(self, featureRequest: QgsFeatureRequest, fids: Any)

Gets called, whenever the full list of feature ids for a certain request is known. Broadcasts this information to indices, so they can update their tables.

Parameters:

• featureRequest (QgsFeatureRequest) – The feature request that was answered

• fids (Any) – The feature ids that have been returned

setCacheAddedAttributes(self, cacheAddedAttributes: bool)

If this is enabled, the subset of cached attributes will automatically be extended to also include newly added attributes.

Parameters:

cacheAddedAttributes (bool) – Automatically cache new attributes

setCacheGeometry(self, cacheGeometry: bool)

Enable or disable the caching of geometries

Parameters:

cacheGeometry (bool) – Enable or disable the caching of geometries

See also

cacheGeometry()

setCacheSize(self, cacheSize: int)

Sets the maximum number of features to keep in the cache. Some features will be removed from the cache if the number is smaller than the previous size of the cache.

Parameters:

cacheSize (int) – indicates the maximum number of features to keep in the cache

setCacheSubsetOfAttributes(self, attributes: Iterable[int])

Set the list (possibly a subset) of attributes to be cached.

Note

By default the cache will store all layer’s attributes.

Parameters:

attributes (Iterable[int]) – The attributes to be cached

setFullCache(self, fullCache: bool)

This enables or disables full caching. If enabled, all features will be held in the cache. The cache size will incrementally be increased to offer space for all features. When enabled, all features will be read into cache. As this feature will most likely be used for slow data sources, be aware, that the call to this method might take a long time.

Parameters:

fullCache (bool) – True: enable full caching, False: disable full caching

Note

when a cache is invalidated() (e.g. by adding an attribute to a layer) this setting is reset. A full cache rebuild must be performed by calling setFullCache( True ) again.

See also

hasFullCache()

sourceCrs(self) → QgsCoordinateReferenceSystem

Returns the coordinate reference system for features in the cache.

Return type:

QgsCoordinateReferenceSystem

wkbType(self) → Qgis.WkbType

Returns the geometry type for features in the cache.

Return type:

Qgis.WkbType