Class: QgsVectorLayerCache¶
- class qgis.core.QgsVectorLayerCache¶
Bases:
PyQt5.QtCore.QObject
This class caches features of a given
QgsVectorLayer
.The cached features can be indexed by
QgsAbstractCacheIndex
.Proper indexing for a given use-case may speed up performance substantially.
Methods
Adds a
QgsAbstractCacheIndex
to this cache.Returns
True
if the cache will fetch and cache feature geometries.Returns the maximum number of features this cache will hold.
Returns the set of feature IDs for features which are cached.
Checks if the information required to complete the request is cached.
Gets the feature at the given feature id.
Returns the number of features contained in the source, or -1 if the feature count is unknown.
Gets called, whenever a feature has been removed.
Returns the fields associated with features in the cache.
Query the layer for the feature with the given id.
Query this VectorLayerCache for features.
Returns
True
if the cache is complete, ie it contains all features.Check if a certain feature id is cached.
Returns the layer to which this cache belongs
Removes the feature identified by fid from the cache if present.
Gets called, whenever the full list of feature ids for a certain request is known.
If this is enabled, the subset of cached attributes will automatically be extended to also include newly added attributes.
Enable or disable the caching of geometries
Sets the maximum number of features to keep in the cache.
Set the subset of attributes to be cached
This enables or disables full caching.
Returns the coordinate reference system for features in the cache.
Returns the geometry type for features in the cache.
Signals
Emitted when an attribute is changed.
Is emitted when the cached layer is deleted.
Emitted when a new feature has been added to the layer and this cache.
When filling the cache, this signal gets emitted once the cache is fully initialized.
The cache has been invalidated and cleared.
- addCacheIndex(self, cacheIndex: QgsAbstractCacheIndex)¶
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 aQgsFeatureRequest
. The layer cache will take ownership of the index.- Parameters
cacheIndex (QgsAbstractCacheIndex) – The cache index to add.
- attributeValueChanged¶
Emitted when an attribute is changed. Is re-emitted after the layer itself emits this signal. You should connect to this signal, to be sure, to not get a cached value if querying the cache. [signal]
- Parameters
fid (int) –
field (int) –
value (Any) –
- cacheGeometry(self) bool ¶
Returns
True
if the cache will fetch and cache feature geometries.See also
New in version 3.0.
- 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
- cachedFeatureIds(self) object ¶
Returns the set of feature IDs for features which are cached.
See also
New in version 3.0.
- Return type
object
- cachedLayerDeleted¶
Is emitted when the cached layer is deleted. Is emitted when the cached layers
layerDelete()
signal is being emitted, but before the local reference to it has been set toNone
. So call tolayer()
will still return a valid pointer for cleanup purpose. [signal]
- 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
- childEvent(self, QChildEvent)¶
- connectNotify(self, QMetaMethod)¶
- customEvent(self, QEvent)¶
- disconnectNotify(self, QMetaMethod)¶
- featureAdded¶
Emitted when a new feature has been added to the layer and this cache. You should connect to this signal instead of the layers’, if you want to be sure that this cache has updated information for the new feature
- Parameters
fid (int) – The featureid of the changed feature [signal]
- featureAtId(self, featureId: int, feature: QgsFeature, skipCache: bool = False) bool ¶
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
feature (QgsFeature) – The result of the operation will be written to this feature
skipCache (bool = False) – Will query the layer regardless if the feature is in the cache already
- Return type
bool
- Returns
True
in case of success
- 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.
- finished¶
When filling the cache, this signal gets emitted once the cache is fully initialized. [signal]
- 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
- 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
- Returns
An iterator over the requested data.
getFeatures(self, expression: str) -> QgsFeatureIterator Query the layer for features matching a given expression.
getFeatures(self, fids: object) -> 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 tosetFullCache()
or by through a feature request which resulted in all available features being cached.See also
New in version 3.0.
- Return type
bool
- invalidated¶
The cache has been invalidated and cleared. Note that when a cache is invalidated the
fullCache()
setting will be cleared, and a full cache rebuild via setFullCache(True
) will need to be performed. [signal]
- 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
- isSignalConnected(self, QMetaMethod) bool ¶
- layer(self) QgsVectorLayer ¶
Returns the layer to which this cache belongs
- Return type
- receivers(self, PYQT_SIGNAL) int ¶
- 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: object)¶
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 (object) – The feature ids that have been returned
- sender(self) QObject ¶
- senderSignalIndex(self) int ¶
- 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
- 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 subset of attributes to be cached
- 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
- sourceCrs(self) QgsCoordinateReferenceSystem ¶
Returns the coordinate reference system for features in the cache.
- Return type
- timerEvent(self, QTimerEvent)¶
- wkbType(self) QgsWkbTypes.Type ¶
Returns the geometry type for features in the cache.
- Return type