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

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. More...
 
int cacheSize ()
 Returns the maximum number of features this cache will hold. More...
 
void setCacheGeometry (bool cacheGeometry)
 Enable or disable the caching of geometries. More...
 
void setCacheSubsetOfAttributes (const QgsAttributeList &attributes)
 Set the subset of attributes to be cached. 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 setFullCache (bool fullCache)
 This enables or disables full caching. More...
 
void addCacheIndex (QgsAbstractCacheIndex *cacheIndex)
 Adds a QgsAbstractCacheIndex to this cache. More...
 
QgsFeatureIterator getFeatures (const QgsFeatureRequest &featureRequest=QgsFeatureRequest())
 Query this VectorLayerCache for features. More...
 
bool isFidCached (const QgsFeatureId fid)
 Check if a certain feature id is cached. More...
 
bool featureAtId (QgsFeatureId featureId, QgsFeature &feature, bool skipCache=false)
 Gets the feature at the given feature id. More...
 
bool removeCachedFeature (QgsFeatureId fid)
 Removes the feature identified by fid from the cache if present. More...
 
QgsVectorLayerlayer ()
 Returns the layer to which this cache belongs. More...
 

Protected Member Functions

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

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
cacheIndexThe 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
featureRequestThe 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
fidThe 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
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
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.
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
featureRequestThe 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
fidThe 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
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
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
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
featureRequestThe feature request that was answered
fidsThe 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
cacheAddedAttributesAutomatically cache new attributes
void QgsVectorLayerCache::setCacheGeometry ( bool  cacheGeometry)

Enable or disable the caching of geometries.

Parameters
cacheGeometryEnable 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
cacheSizeindicates 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
attributesThe 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
fullCacheTrue: 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: