QGIS API Documentation  2.99.0-Master (08ee180)
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QgsVectorLayerCache Class Reference

This class caches features of a given QgsVectorLayer. More...

#include <qgsvectorlayercache.h>

Inheritance diagram for QgsVectorLayerCache:
Inheritance graph
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Signals

void attributeValueChanged (QgsFeatureId fid, int field, const QVariant &value)
 Is emitted when an attribute is changed. More...
 
void cachedLayerDeleted ()
 Is emitted when the cached layer is deleted. More...
 
void featureAdded (QgsFeatureId fid)
 Is emitted, when a new feature has been added to the layer and this cache. More...
 
void finished ()
 When filling the cache, this signal gets emitted once the cache is fully initialized. More...
 
void invalidated ()
 The cache has been invalidated and cleared. More...
 
void progress (int i, bool &cancel)
 When filling the cache, this signal gets emitted periodically to notify about the progress and to be able to cancel an operation. More...
 

Public Member Functions

 QgsVectorLayerCache (QgsVectorLayer *layer, int cacheSize, QObject *parent=nullptr)
 
 ~QgsVectorLayerCache ()
 
void addCacheIndex (QgsAbstractCacheIndex *cacheIndex)
 Adds a QgsAbstractCacheIndex to this cache. More...
 
QgsFeatureIds cachedFeatureIds () const
 Returns the set of feature IDs for features which are cached. More...
 
int cacheSize ()
 Returns the maximum number of features this cache will hold. More...
 
bool featureAtId (QgsFeatureId featureId, QgsFeature &feature, bool skipCache=false)
 Gets the feature at the given feature id. More...
 
QgsFeature getFeature (QgsFeatureId fid)
 Query the layer for the feature with the given id. More...
 
QgsFeatureIterator getFeatures (const QgsFeatureRequest &featureRequest=QgsFeatureRequest())
 Query this VectorLayerCache for features. More...
 
QgsFeatureIterator getFeatures (const QString &expression)
 Query the layer for features matching a given expression. More...
 
QgsFeatureIterator getFeatures (const QgsFeatureIds &fids)
 Query the layer for the features with the given ids. More...
 
QgsFeatureIterator getFeatures (const QgsRectangle &rectangle)
 Query the layer for the features which intersect the specified rectangle. More...
 
bool hasFullCache () const
 Returns true if the cache is complete, ie it contains all features. More...
 
bool isFidCached (const QgsFeatureId fid) const
 Check if a certain feature id is cached. More...
 
QgsVectorLayerlayer ()
 Returns the layer to which this cache belongs. More...
 
bool removeCachedFeature (QgsFeatureId fid)
 Removes the feature identified by fid from the cache if present. More...
 
void setCacheAddedAttributes (bool cacheAddedAttributes)
 If this is enabled, the subset of cached attributes will automatically be extended to also include newly added attributes. More...
 
void setCacheGeometry (bool cacheGeometry)
 Enable or disable the caching of geometries. More...
 
void setCacheSize (int cacheSize)
 Sets the maximum number of features to keep in the cache. More...
 
void setCacheSubsetOfAttributes (const QgsAttributeList &attributes)
 Set the subset of attributes to be cached. More...
 
void setFullCache (bool fullCache)
 This enables or disables full caching. More...
 

Protected Member Functions

bool checkInformationCovered (const QgsFeatureRequest &featureRequest)
 Checks if the information required to complete the request is cached. More...
 
void featureRemoved (QgsFeatureId fid)
 Gets called, whenever a feature has been removed. More...
 
void requestCompleted (const QgsFeatureRequest &featureRequest, const QgsFeatureIds &fids)
 Gets called, whenever the full list of feature ids for a certain request is known. More...
 

Friends

class QgsCachedFeature
 
class QgsCachedFeatureIterator
 
class QgsCachedFeatureWriterIterator
 
class TestVectorLayerCache
 

Detailed Description

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.

Definition at line 38 of file qgsvectorlayercache.h.

Constructor & Destructor Documentation

§ QgsVectorLayerCache()

QgsVectorLayerCache::QgsVectorLayerCache ( QgsVectorLayer layer,
int  cacheSize,
QObject *  parent = nullptr 
)

Definition at line 22 of file qgsvectorlayercache.cpp.

§ ~QgsVectorLayerCache()

QgsVectorLayerCache::~QgsVectorLayerCache ( )

Definition at line 43 of file qgsvectorlayercache.cpp.

Member Function Documentation

§ addCacheIndex()

void QgsVectorLayerCache::addCacheIndex ( QgsAbstractCacheIndex cacheIndex)

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
cacheIndexThe cache index to add.

Definition at line 118 of file qgsvectorlayercache.cpp.

§ attributeValueChanged

void QgsVectorLayerCache::attributeValueChanged ( QgsFeatureId  fid,
int  field,
const QVariant &  value 
)
signal

Is 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.

§ cachedFeatureIds()

QgsFeatureIds QgsVectorLayerCache::cachedFeatureIds ( ) const
inline

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

Note
added in QGIS 3.0
See also
isFidCached()

Definition at line 216 of file qgsvectorlayercache.h.

§ cachedLayerDeleted

void QgsVectorLayerCache::cachedLayerDeleted ( )
signal

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 to NULL. So call to layer() will still return a valid pointer for cleanup purpose.

§ cacheSize()

int QgsVectorLayerCache::cacheSize ( )

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.

Returns
int

Definition at line 54 of file qgsvectorlayercache.cpp.

§ checkInformationCovered()

bool QgsVectorLayerCache::checkInformationCovered ( const QgsFeatureRequest featureRequest)
protected

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
featureRequestThe QgsFeatureRequest to be answered
Returns
True if the information is being cached, false if not

Definition at line 372 of file qgsvectorlayercache.cpp.

§ featureAdded

void QgsVectorLayerCache::featureAdded ( QgsFeatureId  fid)
signal

Is 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
fidThe featureid of the changed feature

§ featureAtId()

bool QgsVectorLayerCache::featureAtId ( QgsFeatureId  featureId,
QgsFeature feature,
bool  skipCache = false 
)

Gets the feature at the given feature id.

Considers the changed, added, deleted and permanent features

Parameters
featureIdThe id of the feature to query
featureThe result of the operation will be written to this feature
skipCacheWill query the layer regardless if the feature is in the cache already
Returns
true in case of success

Definition at line 135 of file qgsvectorlayercache.cpp.

§ featureRemoved()

void QgsVectorLayerCache::featureRemoved ( QgsFeatureId  fid)
protected

Gets called, whenever a feature has been removed.

Broadcasts this information to indices, so they can invalidate their cache if required.

Parameters
fidThe feature id of the removed feature.

Definition at line 190 of file qgsvectorlayercache.cpp.

§ finished

void QgsVectorLayerCache::finished ( )
signal

When filling the cache, this signal gets emitted once the cache is fully initialized.

§ getFeature()

QgsFeature QgsVectorLayerCache::getFeature ( QgsFeatureId  fid)
inline

Query the layer for the feature with the given id.

If there is no such feature, the returned feature will be invalid.

Definition at line 181 of file qgsvectorlayercache.h.

§ getFeatures() [1/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QgsFeatureRequest featureRequest = QgsFeatureRequest())

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
featureRequestThe request specifying filter and required data.
Returns
An iterator over the requested data.

Definition at line 321 of file qgsvectorlayercache.cpp.

§ getFeatures() [2/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QString &  expression)
inline

Query the layer for features matching a given expression.

Definition at line 172 of file qgsvectorlayercache.h.

§ getFeatures() [3/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QgsFeatureIds fids)
inline

Query the layer for the features with the given ids.

Definition at line 191 of file qgsvectorlayercache.h.

§ getFeatures() [4/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QgsRectangle rectangle)
inline

Query the layer for the features which intersect the specified rectangle.

Definition at line 199 of file qgsvectorlayercache.h.

§ hasFullCache()

bool QgsVectorLayerCache::hasFullCache ( ) const
inline

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()
Note
added in QGIS 3.0

Definition at line 146 of file qgsvectorlayercache.h.

§ invalidated

void QgsVectorLayerCache::invalidated ( )
signal

The cache has been invalidated and cleared.

§ isFidCached()

bool QgsVectorLayerCache::isFidCached ( const QgsFeatureId  fid) const

Check if a certain feature id is cached.

Parameters
fidThe feature id to look for
Returns
True if this id is in the cache
See also
cachedFeatureIds()

Definition at line 367 of file qgsvectorlayercache.cpp.

§ layer()

QgsVectorLayer * QgsVectorLayerCache::layer ( )

Returns the layer to which this cache belongs.

Definition at line 169 of file qgsvectorlayercache.cpp.

§ progress

void QgsVectorLayerCache::progress ( int  i,
bool &  cancel 
)
signal

When filling the cache, this signal gets emitted periodically to notify about the progress and to be able to cancel an operation.

Parameters
iThe number of already fetched features
cancelA reference to a boolean variable. Set to true and the operation will be canceled.
Note
not available in python bindings

§ removeCachedFeature()

bool QgsVectorLayerCache::removeCachedFeature ( QgsFeatureId  fid)

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

Parameters
fidThe id of the feature to delete
Returns
true if the feature was removed, false if the feature id was not found in the cache

Definition at line 164 of file qgsvectorlayercache.cpp.

§ requestCompleted()

void QgsVectorLayerCache::requestCompleted ( const QgsFeatureRequest featureRequest,
const QgsFeatureIds fids 
)
protected

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
featureRequestThe feature request that was answered
fidsThe feature ids that have been returned

Definition at line 174 of file qgsvectorlayercache.cpp.

§ setCacheAddedAttributes()

void QgsVectorLayerCache::setCacheAddedAttributes ( bool  cacheAddedAttributes)

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

Parameters
cacheAddedAttributesAutomatically cache new attributes

Definition at line 123 of file qgsvectorlayercache.cpp.

§ setCacheGeometry()

void QgsVectorLayerCache::setCacheGeometry ( bool  cacheGeometry)

Enable or disable the caching of geometries.

Parameters
cacheGeometryEnable or disable the caching of geometries

Definition at line 59 of file qgsvectorlayercache.cpp.

§ setCacheSize()

void QgsVectorLayerCache::setCacheSize ( int  cacheSize)

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
cacheSizeindicates the maximum number of features to keep in the cache

Definition at line 49 of file qgsvectorlayercache.cpp.

§ setCacheSubsetOfAttributes()

void QgsVectorLayerCache::setCacheSubsetOfAttributes ( const QgsAttributeList attributes)

Set the subset of attributes to be cached.

Parameters
attributesThe attributes to be cached

Definition at line 72 of file qgsvectorlayercache.cpp.

§ setFullCache()

void QgsVectorLayerCache::setFullCache ( bool  fullCache)

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
fullCacheTrue: enable full caching, False: disable full caching
See also
hasFullCache()

Definition at line 77 of file qgsvectorlayercache.cpp.

Friends And Related Function Documentation

§ QgsCachedFeature

friend class QgsCachedFeature
friend

Definition at line 347 of file qgsvectorlayercache.h.

§ QgsCachedFeatureIterator

friend class QgsCachedFeatureIterator
friend

Definition at line 345 of file qgsvectorlayercache.h.

§ QgsCachedFeatureWriterIterator

friend class QgsCachedFeatureWriterIterator
friend

Definition at line 346 of file qgsvectorlayercache.h.

§ TestVectorLayerCache

friend class TestVectorLayerCache
friend

Definition at line 358 of file qgsvectorlayercache.h.


The documentation for this class was generated from the following files: