QgsVectorLayerCache Class Reference

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

#include <qgsvectorlayercache.h>

Inheritance diagram for QgsVectorLayerCache:

Signals
void	attributeValueChanged (QgsFeatureId fid, int field, const QVariant &value)
	Emitted when an attribute is changed. More...
void	cachedLayerDeleted ()
	Is emitted when the cached layer is deleted. More...
void	featureAdded (QgsFeatureId fid)
	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 () override
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...
bool	cacheGeometry () const
	Returns true if the cache will fetch and cache feature geometries. 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...
long long	featureCount () const
	Returns the number of features contained in the source, or -1 if the feature count is unknown. More...
QgsFields	fields () const
	Returns the fields associated with features in the cache. More...
QgsFeature	getFeature (QgsFeatureId fid)
	Query the layer for the feature with the given id. More...
QgsFeatureIterator	getFeatures (const QgsFeatureIds &fids)
	Query the layer for the features with the given ids. More...
QgsFeatureIterator	getFeatures (const QgsFeatureRequest &featureRequest=QgsFeatureRequest())
	Query this VectorLayerCache for features. More...
QgsFeatureIterator	getFeatures (const QgsRectangle &rectangle)
	Query the layer for the features which intersect the specified rectangle. More...
QgsFeatureIterator	getFeatures (const QString &expression)
	Query the layer for features matching a given expression. More...
bool	hasFullCache () const
	Returns true if the cache is complete, ie it contains all features. More...
bool	isFidCached (QgsFeatureId fid) const
	Check if a certain feature id is cached. More...
QgsVectorLayer *	layer ()
	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...
QgsCoordinateReferenceSystem	sourceCrs () const
	Returns the coordinate reference system for features in the cache. More...
QgsWkbTypes::Type	wkbType () const
	Returns the geometry type for features in the cache. 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 46 of file qgsvectorlayercache.h.

Constructor & Destructor Documentation

QgsVectorLayerCache()

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

Definition at line 27 of file qgsvectorlayercache.cpp.

~QgsVectorLayerCache()

QgsVectorLayerCache::~QgsVectorLayerCache ( )

override

Definition at line 49 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

cacheIndex

The cache index to add.

Definition at line 130 of file qgsvectorlayercache.cpp.

attributeValueChanged

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

signal

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

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

See also

isFidCached()

Since

QGIS 3.0

Definition at line 454 of file qgsvectorlayercache.cpp.

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

cacheGeometry()

bool QgsVectorLayerCache::cacheGeometry ( ) const

inline

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

See also

setCacheGeometry()

Since

QGIS 3.0

Definition at line 125 of file qgsvectorlayercache.h.

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 60 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

featureRequest

The QgsFeatureRequest to be answered

Returns

true if the information is being cached, false if not

Definition at line 460 of file qgsvectorlayercache.cpp.

featureAdded

void QgsVectorLayerCache::featureAdded ( QgsFeatureId  fid )

signal

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	The 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

featureId	The id of the feature to query
feature	The result of the operation will be written to this feature
skipCache	Will query the layer regardless if the feature is in the cache already

Returns

true in case of success

Definition at line 147 of file qgsvectorlayercache.cpp.

featureCount()

long long QgsVectorLayerCache::featureCount

(

)

const

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

Definition at line 212 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

fid	The feature id of the removed feature.

Definition at line 234 of file qgsvectorlayercache.cpp.

fields()

QgsFields QgsVectorLayerCache::fields

(

)

const

Returns the fields associated with features in the cache.

Definition at line 207 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 199 of file qgsvectorlayercache.h.

getFeatures() [1/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QgsFeatureIds &  fids )

inline

Query the layer for the features with the given ids.

Definition at line 209 of file qgsvectorlayercache.h.

getFeatures() [2/4]

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

featureRequest

The request specifying filter and required data.

Returns

An iterator over the requested data.

Definition at line 400 of file qgsvectorlayercache.cpp.

getFeatures() [3/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QgsRectangle &  rectangle )

inline

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

Definition at line 217 of file qgsvectorlayercache.h.

getFeatures() [4/4]

QgsFeatureIterator QgsVectorLayerCache::getFeatures ( const QString &  expression )

inline

Query the layer for features matching a given expression.

Definition at line 190 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()

Since

QGIS 3.0

Definition at line 164 of file qgsvectorlayercache.h.

invalidated

void QgsVectorLayerCache::invalidated ( )

signal

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.

isFidCached()

bool QgsVectorLayerCache::isFidCached

(

QgsFeatureId

fid

)

const

Check if a certain feature id is cached.

Parameters

fid	The feature id to look for

Returns

true if this id is in the cache

See also

cachedFeatureIds()

Definition at line 449 of file qgsvectorlayercache.cpp.

layer()

QgsVectorLayer * QgsVectorLayerCache::layer

(

)

Returns the layer to which this cache belongs.

Definition at line 192 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

i	The number of already fetched features
cancel	A 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

fid	The 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 176 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

featureRequest	The feature request that was answered
fids	The feature ids that have been returned

Definition at line 217 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

cacheAddedAttributes

Automatically cache new attributes

Definition at line 135 of file qgsvectorlayercache.cpp.

setCacheGeometry()

void QgsVectorLayerCache::setCacheGeometry

(

bool

cacheGeometry

)

Enable or disable the caching of geometries.

Parameters

cacheGeometry

Enable or disable the caching of geometries

See also

cacheGeometry()

Definition at line 65 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

cacheSize

indicates the maximum number of features to keep in the cache

Definition at line 55 of file qgsvectorlayercache.cpp.

setCacheSubsetOfAttributes()

void QgsVectorLayerCache::setCacheSubsetOfAttributes

(

const QgsAttributeList &

attributes

)

Set the subset of attributes to be cached.

Parameters

attributes

The attributes to be cached

Definition at line 84 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

fullCache

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()

Definition at line 89 of file qgsvectorlayercache.cpp.

sourceCrs()

QgsCoordinateReferenceSystem QgsVectorLayerCache::sourceCrs

(

)

const

Returns the coordinate reference system for features in the cache.

Definition at line 197 of file qgsvectorlayercache.cpp.

wkbType()

QgsWkbTypes::Type QgsVectorLayerCache::wkbType

(

)

const

Returns the geometry type for features in the cache.

Definition at line 202 of file qgsvectorlayercache.cpp.

Friends And Related Function Documentation

QgsCachedFeature

friend class QgsCachedFeature

friend

Definition at line 421 of file qgsvectorlayercache.h.

QgsCachedFeatureIterator

friend class QgsCachedFeatureIterator

friend

Definition at line 419 of file qgsvectorlayercache.h.

QgsCachedFeatureWriterIterator

friend class QgsCachedFeatureWriterIterator

friend

Definition at line 420 of file qgsvectorlayercache.h.

TestVectorLayerCache

friend class TestVectorLayerCache

friend

Definition at line 433 of file qgsvectorlayercache.h.

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

• /build/qgis-3.28.0+99sid/src/core/vector/qgsvectorlayercache.h
• /build/qgis-3.28.0+99sid/src/core/vector/qgsvectorlayercache.cpp