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

#include <qgsvectorlayercache.h>

Classes
class	QgsCachedFeature
	This is a wrapper class around a cached QgsFeature, which will inform the cache, when it has been deleted, so indexes can be updated that the wrapped feature needs to be fetched again if needed.

Signals
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.
void	finished ()
	When filling the cache, this signal gets emitted once the cache is fully initialized.
void	cachedLayerDeleted ()
	Is emitted when the cached layer is deleted.
void	attributeValueChanged (const QgsFeatureId &fid, const int &field, const QVariant &value)
	Is emitted when an attribute is changed.
void	featureAdded (QgsFeatureId fid)
	Is emitted, when a new feature has been added to the layer and this cache.

Public Member Functions
	QgsVectorLayerCache (QgsVectorLayer layer, int cacheSize, QObject parent=NULL)
	~QgsVectorLayerCache ()
void	setCacheSize (int cacheSize)
	Sets the maximum number of features to keep in the cache.
int	cacheSize ()
	Returns the maximum number of features this cache will hold.
void	setCacheGeometry (bool cacheGeometry)
	Enable or disable the caching of geometries.
void	setCacheSubsetOfAttributes (const QgsAttributeList &attributes)
	Set the subset of attributes to be cached.
void	setCacheAddedAttributes (bool cacheAddedAttributes)
	If this is enabled, the subset of cached attributes will automatically be extended to also include newly added attributes.
void	setFullCache (bool fullCache)
	This enables or disables full caching.
void	addCacheIndex (QgsAbstractCacheIndex *cacheIndex)
	Adds a QgsAbstractCacheIndex to this cache.
QgsFeatureIterator	getFeatures (const QgsFeatureRequest &featureRequest=QgsFeatureRequest())
	Query this VectorLayerCache for features.
bool	isFidCached (const QgsFeatureId fid)
	Check if a certain feature id is cached.
bool	featureAtId (QgsFeatureId featureId, QgsFeature &feature, bool skipCache=false)
	Gets the feature at the given feature id.
bool	removeCachedFeature (QgsFeatureId fid)
	Removes the feature identified by fid from the cache if present.
QgsVectorLayer *	layer ()
	Returns the layer to which this cache belongs.

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

Friends
class	QgsCachedFeatureIterator
class	QgsCachedFeatureWriterIterator
class	QgsCachedFeature

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.

Constructor & Destructor Documentation

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

QgsVectorLayerCache::~QgsVectorLayerCache ( )

Member Function Documentation

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.

void QgsVectorLayerCache::attributeValueChanged	(	const QgsFeatureId &	fid,
		const 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.

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.

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

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

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

fid	The featureid of the changed feature

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

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.

void QgsVectorLayerCache::finished ( )

signal

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

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.

bool QgsVectorLayerCache::isFidCached ( const QgsFeatureId fid )

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

QgsVectorLayer * QgsVectorLayerCache::layer ( )

Returns the layer to which this cache belongs.

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

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

void QgsVectorLayerCache::requestCompleted	(	QgsFeatureRequest	featureRequest,
		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

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

void QgsVectorLayerCache::setCacheGeometry ( bool cacheGeometry )

Enable or disable the caching of geometries.

Parameters

cacheGeometry Enable or disable the caching of geometries

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

void QgsVectorLayerCache::setCacheSubsetOfAttributes ( const QgsAttributeList & attributes )

Set the subset of attributes to be cached.

Parameters

attributes The attributes to be cached

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

Friends And Related Function Documentation

friend class QgsCachedFeature

friend

friend class QgsCachedFeatureIterator

friend

friend class QgsCachedFeatureWriterIterator

friend

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

/tmp/buildd/qgis-2.6.0+wheezy1/src/core/qgsvectorlayercache.h
/tmp/buildd/qgis-2.6.0+wheezy1/src/core/qgsvectorlayercache.cpp

Classes

Signals

Public Member Functions

Protected Member Functions

Friends

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation