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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
[legend]

Signals

void attributeValueChanged (const QgsFeatureId &fid, const 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 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=NULL)
 
 ~QgsVectorLayerCache ()
 
void addCacheIndex (QgsAbstractCacheIndex *cacheIndex)
 Adds a QgsAbstractCacheIndex to this cache. 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...
 
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...
 
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 (QgsFeatureRequest featureRequest, 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
 

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

Definition at line 22 of file qgsvectorlayercache.cpp.

QgsVectorLayerCache::~QgsVectorLayerCache ( )

Definition at line 42 of file qgsvectorlayercache.cpp.

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.

Definition at line 117 of file qgsvectorlayercache.cpp.

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

Definition at line 53 of file qgsvectorlayercache.cpp.

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 319 of file qgsvectorlayercache.cpp.

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

Definition at line 134 of file qgsvectorlayercache.cpp.

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 185 of file qgsvectorlayercache.cpp.

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.

Definition at line 261 of file qgsvectorlayercache.cpp.

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

Definition at line 314 of file qgsvectorlayercache.cpp.

QgsVectorLayer * QgsVectorLayerCache::layer ( )

Returns the layer to which this cache belongs.

Definition at line 168 of file qgsvectorlayercache.cpp.

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

Definition at line 163 of file qgsvectorlayercache.cpp.

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

Definition at line 173 of file qgsvectorlayercache.cpp.

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 122 of file qgsvectorlayercache.cpp.

void QgsVectorLayerCache::setCacheGeometry ( bool  cacheGeometry)

Enable or disable the caching of geometries.

Parameters
cacheGeometryEnable or disable the caching of geometries

Definition at line 58 of file qgsvectorlayercache.cpp.

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 48 of file qgsvectorlayercache.cpp.

void QgsVectorLayerCache::setCacheSubsetOfAttributes ( const QgsAttributeList attributes)

Set the subset of attributes to be cached.

Parameters
attributesThe attributes to be cached

Definition at line 71 of file qgsvectorlayercache.cpp.

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

Definition at line 76 of file qgsvectorlayercache.cpp.

Friends And Related Function Documentation

friend class QgsCachedFeature
friend

Definition at line 288 of file qgsvectorlayercache.h.

friend class QgsCachedFeatureIterator
friend

Definition at line 286 of file qgsvectorlayercache.h.

friend class QgsCachedFeatureWriterIterator
friend

Definition at line 287 of file qgsvectorlayercache.h.


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