QgsVectorLayerJoinInfo class

Defines left outer join from our vector layer to some other vector layer.

Reference

The join is done based on [our layer].targetField = [join layer].joinField

Public static functions

static auto joinFieldNamesSubset(const QgsVectorLayerJoinInfo& info, bool blacklisted = true) -> QStringList: Returns the list of field names to use for joining considering blacklisted fields and subset.

Constructors, destructors, conversion operators

QgsVectorLayerJoinInfo() defaulted: Constructor for QgsVectorLayerJoinInfo.

Public functions

auto extractJoinedFeature(const QgsFeature& feature) const -> QgsFeature: Extract the join feature from the target feature for the current join layer information.
auto hasCascadedDelete() const -> bool: Returns whether a feature deleted on the target layer has to impact the joined layer by deleting the corresponding joined feature.
auto hasSubset(bool blacklisted = true) const -> bool: Returns true if blacklisted fields is not empty or if a subset of names has been set.
auto hasUpsertOnEdit() const -> bool: Returns whether a feature created on the target layer has to impact the joined layer by creating a new feature if necessary.
auto isDynamicFormEnabled() const -> bool: Returns whether the form has to be dynamically updated with joined fields when a feature is being created in the target layer.
auto isEditable() const -> bool: Returns whether joined fields may be edited through the form of the target layer.
auto isUsingMemoryCache() const -> bool: Returns whether values from the joined layer should be cached in memory to speed up lookups.
auto joinFieldName() const -> QString: Returns name of the field of joined layer that will be used for join.
auto joinFieldNamesBlackList() const -> QStringList: Returns the list of fields to ignore.
auto joinFieldNamesSubset() const -> QStringList*: Gets subset of fields to be used from joined layer.
auto joinLayer() const -> QgsVectorLayer*: Returns joined layer (may be null if the reference was set by layer ID and not resolved yet)
auto joinLayerId() const -> QString: ID of the joined layer - may be used to resolve reference to the joined layer.
auto prefix() const -> QString: Returns prefix of fields from the joined layer. If null, joined layer's name will be used.
auto prefixedFieldName(const QgsField& field) const -> QString: Returns the prefixed name of the field.
void setCascadedDelete(bool enabled): Sets whether a feature deleted on the target layer has to impact the joined layer by deleting the corresponding joined feature.
void setDynamicFormEnabled(bool enabled): Sets whether the form has to be dynamically updated with joined fields when a feature is being created in the target layer.
void setEditable(bool enabled): Sets whether the form of the target layer allows editing joined fields.
void setJoinFieldName(const QString& fieldName): Sets name of the field of joined layer that will be used for join.
void setJoinFieldNamesBlackList(const QStringList& blackList): Sets a list of fields to ignore whatever happens.
void setJoinFieldNamesSubset(QStringList* fieldNamesSubset): Set subset of fields to be used from joined layer.
void setJoinLayer(QgsVectorLayer* layer): Sets weak reference to the joined layer.
void setJoinLayerId(const QString& layerId): Sets ID of the joined layer. It will need to be overwritten by setJoinLayer() to a reference to real layer.
void setPrefix(const QString& prefix): Sets prefix of fields from the joined layer. If null, joined layer's name will be used.
void setTargetFieldName(const QString& fieldName): Sets name of the field of our layer that will be used for join.
void setUpsertOnEdit(bool enabled): Sets whether a feature created on the target layer has to impact the joined layer by creating a new feature if necessary.
void setUsingMemoryCache(bool enabled): Sets whether values from the joined layer should be cached in memory to speed up lookups.
auto targetFieldName() const -> QString: Returns name of the field of our layer that will be used for join.

Protected variables

QHash<QString, QgsAttributes> cachedAttributes: Cache for joined attributes to provide fast lookup (size is 0 if no memory caching)
bool cacheDirty: True if the cached join attributes need to be updated.
QString mJoinFieldName: Join field in the source layer.
std::shared_ptr<QStringList> mJoinFieldsSubset: Subset of fields to use from joined layer. null = use all fields.
QgsVectorLayerRef mJoinLayerRef: Weak reference to the joined layer.
bool mMemoryCache: True if the join is cached in virtual memory.
QString mPrefix: An optional prefix.
QString mTargetFieldName: Join field in the target layer.

Function documentation

static QStringList QgsVectorLayerJoinInfo::joinFieldNamesSubset(const QgsVectorLayerJoinInfo& info, bool blacklisted = true)

Returns the list of field names to use for joining considering blacklisted fields and subset.

QgsFeature QgsVectorLayerJoinInfo::extractJoinedFeature(const QgsFeature& feature) const

Extract the join feature from the target feature for the current join layer information.

Parameters
feature	A feature from the target layer
Returns	the corresponding joined feature

bool QgsVectorLayerJoinInfo::hasCascadedDelete() const

Returns whether a feature deleted on the target layer has to impact the joined layer by deleting the corresponding joined feature.

bool QgsVectorLayerJoinInfo::hasSubset(bool blacklisted = true) const

Returns true if blacklisted fields is not empty or if a subset of names has been set.

bool QgsVectorLayerJoinInfo::hasUpsertOnEdit() const

Returns whether a feature created on the target layer has to impact the joined layer by creating a new feature if necessary.

bool QgsVectorLayerJoinInfo::isDynamicFormEnabled() const

Returns whether the form has to be dynamically updated with joined fields when a feature is being created in the target layer.

bool QgsVectorLayerJoinInfo::isEditable() const

Returns whether joined fields may be edited through the form of the target layer.

QStringList QgsVectorLayerJoinInfo::joinFieldNamesBlackList() const

Returns the list of fields to ignore.

QStringList* QgsVectorLayerJoinInfo::joinFieldNamesSubset() const

Gets subset of fields to be used from joined layer.

All fields will be used if null is returned.

QString QgsVectorLayerJoinInfo::prefixedFieldName(const QgsField& field) const

Returns the prefixed name of the field.

Parameters
field	the field
Returns	the prefixed name of the field

void QgsVectorLayerJoinInfo::setCascadedDelete(bool enabled)

Sets whether a feature deleted on the target layer has to impact the joined layer by deleting the corresponding joined feature.

void QgsVectorLayerJoinInfo::setDynamicFormEnabled(bool enabled)

Sets whether the form has to be dynamically updated with joined fields when a feature is being created in the target layer.

void QgsVectorLayerJoinInfo::setEditable(bool enabled)

Sets whether the form of the target layer allows editing joined fields.

void QgsVectorLayerJoinInfo::setJoinFieldNamesBlackList(const QStringList& blackList)

Sets a list of fields to ignore whatever happens.

void QgsVectorLayerJoinInfo::setJoinFieldNamesSubset(QStringList* fieldNamesSubset)

Set subset of fields to be used from joined layer.

Takes ownership of the passed pointer. Null pointer tells to use all fields.

void QgsVectorLayerJoinInfo::setUpsertOnEdit(bool enabled)

Sets whether a feature created on the target layer has to impact the joined layer by creating a new feature if necessary.

Variable documentation

QString QgsVectorLayerJoinInfo::mPrefix protected

An optional prefix.

If it is a Null string "{layername}_" will be used