Represents a relationship between two vector layers. More...

#include <qgsrelation.h>

Classes
class	FieldPair
	Defines a relation between matching fields of the two involved tables of a relation. More...

Public Member Functions
	QgsRelation ()
	Default constructor.

	QgsRelation (const QgsRelation &other)
	Copies a relation.

	QgsRelation (const QgsRelationContext &context)
	Constructor with context.

	~QgsRelation ()

void	addFieldPair (const FieldPair &fieldPair)
	Add a field pair which is part of this relation The first element of each pair are the field names of the foreign key.

void	addFieldPair (const QString &referencingField, const QString &referencedField)
	Add a field pair which is part of this relation The first element of each pair are the field names of the foreign key.

QList< QgsRelation::FieldPair >	fieldPairs () const
	Returns the field pairs which form this relation The first element of each pair are the field names of the foreign key.

void	generateId ()
	Generate a (project-wide) unique id for this relation.

QgsFeature	getReferencedFeature (const QgsFeature &feature) const
	Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

QgsFeatureRequest	getReferencedFeatureRequest (const QgsAttributes &attributes) const
	Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

QgsFeatureRequest	getReferencedFeatureRequest (const QgsFeature &feature) const
	Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

QgsFeatureIterator	getRelatedFeatures (const QgsFeature &feature) const
	Creates an iterator which returns all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

QString	getRelatedFeaturesFilter (const QgsFeature &feature) const
	Returns a filter expression which returns all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

QgsFeatureRequest	getRelatedFeaturesRequest (const QgsFeature &feature) const
	Creates a request to return all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

bool	hasEqualDefinition (const QgsRelation &other) const
	Compares the two QgsRelation, ignoring the name and the ID.

QString	id () const
	A (project-wide) unique id for this relation.

bool	isValid () const
	Returns the validity of this relation.

QString	name () const
	Returns a human readable name for this relation.

QgsRelation &	operator= (const QgsRelation &other)
	Copies a relation.

QgsPolymorphicRelation	polymorphicRelation () const
	Returns the parent polymorphic relation.

QString	polymorphicRelationId () const
	Returns the parent polymorphic relation id.

QgsAttributeList	referencedFields () const
	Returns a list of attributes used to form the referenced fields (most likely primary key) on the referenced (parent) layer.

QgsVectorLayer *	referencedLayer () const
	Access the referenced (parent) layer.

QString	referencedLayerId () const
	Access the referenced (parent) layer's id.

QgsAttributeList	referencingFields () const
	Returns a list of attributes used to form the referencing fields (foreign key) on the referencing (child) layer.

bool	referencingFieldsAllowNull () const
	Returns `true` if none of the referencing fields has a NOT NULL constraint.

QgsVectorLayer *	referencingLayer () const
	Access the referencing (child) layer This is the layer which has the field(s) which point to another layer.

QString	referencingLayerId () const
	Access the referencing (child) layer's id This is the layer which has the field(s) which point to another layer.

Q_INVOKABLE QString	resolveReferencedField (const QString &referencingField) const
	Gets the referenced field counterpart given a referencing field.

Q_INVOKABLE QString	resolveReferencingField (const QString &referencedField) const
	Gets the referencing field counterpart given a referenced field.

void	setId (const QString &id)
	Set an id for this relation.

void	setName (const QString &name)
	Set a name for this relation.

void	setPolymorphicRelationId (const QString &polymorphicRelationId)
	Sets the parent polymorphic relation id.

void	setReferencedLayer (const QString &id)
	Set the referenced (parent) layer id.

void	setReferencingLayer (const QString &id)
	Set the referencing (child) layer id.

void	setStrength (Qgis::RelationshipStrength strength)
	Set a strength for this relation.

Qgis::RelationshipStrength	strength () const
	Returns the relation strength as a string.

Qgis::RelationshipType	type () const
	Returns the type of the relation.

void	updateRelationStatus ()
	Updates the validity status of this relation.

QString	validationError () const
	Returns a user-friendly explanation for why the relationship is invalid.

void	writeXml (QDomNode &node, QDomDocument &doc) const
	Writes a relation to an XML structure.

Static Public Member Functions
static QString	cardinalityToDisplayString (Qgis::RelationshipCardinality cardinality)
	Returns a user-friendly translated string representing a relationship cardinality.

static QgsRelation	createFromXml (const QDomNode &node, QgsReadWriteContext &context, const QgsRelationContext &relationContext=QgsRelationContext())
	Creates a relation from an XML structure.

static QString	strengthToDisplayString (Qgis::RelationshipStrength strength)
	Returns a user-friendly translated string representing a relationship strength.

Properties
QString	id

bool	isValid

QString	name

QgsPolymorphicRelation	polymorphicRelation

QString	polymorphicRelationId

QgsVectorLayer *	referencedLayer

QgsVectorLayer *	referencingLayer

Detailed Description

Represents a relationship between two vector layers.

Definition at line 43 of file qgsrelation.h.

Constructor & Destructor Documentation

◆ QgsRelation() [1/3]

QgsRelation::QgsRelation ( )

Default constructor.

Creates an invalid relation.

Definition at line 29 of file qgsrelation.cpp.

◆ ~QgsRelation()

QgsRelation::~QgsRelation ( )

default

◆ QgsRelation() [2/3]

QgsRelation::QgsRelation ( const QgsRelationContext & context )

Constructor with context.

Creates an invalid relation.

Definition at line 34 of file qgsrelation.cpp.

◆ QgsRelation() [3/3]

QgsRelation::QgsRelation ( const QgsRelation & other )

Copies a relation.

This makes a shallow copy, relations are implicitly shared and only duplicated when the copy is changed.

Definition at line 42 of file qgsrelation.cpp.

Member Function Documentation

◆ addFieldPair() [1/2]

void QgsRelation::addFieldPair ( const FieldPair & fieldPair )

Add a field pair which is part of this relation The first element of each pair are the field names of the foreign key.

The second element of each pair are the field names of the matching primary key.

Parameters

fieldPair A pair of two strings

Note: not available in Python bindings

Definition at line 183 of file qgsrelation.cpp.

◆ addFieldPair() [2/2]

void QgsRelation::addFieldPair	(	const QString &	referencingField,
		const QString &	referencedField
	)

Add a field pair which is part of this relation The first element of each pair are the field names of the foreign key.

The second element of each pair are the field names of the matching primary key.

Parameters

referencingField	The field name on the referencing (child) layer (FK)
referencedField	The field name on the referenced (parent) layer (PK)

Definition at line 176 of file qgsrelation.cpp.

◆ cardinalityToDisplayString()

QString QgsRelation::cardinalityToDisplayString ( Qgis::RelationshipCardinality cardinality )

static

Returns a user-friendly translated string representing a relationship cardinality.

Since: QGIS 3.28

Definition at line 524 of file qgsrelation.cpp.

◆ createFromXml()

QgsRelation QgsRelation::createFromXml	(	const QDomNode &	node,
		QgsReadWriteContext &	context,
		const QgsRelationContext &	relationContext = `QgsRelationContext()`
	)

static

Creates a relation from an XML structure.

Used for reading .qgs projects.

Parameters

node	The dom node containing the relation information
context	to pass project translator
relationContext	a relation context

Returns: A relation

Definition at line 55 of file qgsrelation.cpp.

◆ fieldPairs()

QList< QgsRelation::FieldPair > QgsRelation::fieldPairs ( ) const

Returns the field pairs which form this relation The first element of each pair are the field names of the foreign key.

The second element of each pair are the field names of the matching primary key.

Returns: The fields forming the relation

Definition at line 332 of file qgsrelation.cpp.

◆ generateId()

void QgsRelation::generateId ( )

Generate a (project-wide) unique id for this relation.

Definition at line 298 of file qgsrelation.cpp.

◆ getReferencedFeature()

QgsFeature QgsRelation::getReferencedFeature ( const QgsFeature & feature ) const

Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

Parameters

feature A feature from the referencing (child) layer

Returns: A request the referenced feature

Definition at line 274 of file qgsrelation.cpp.

◆ getReferencedFeatureRequest() [1/2]

QgsFeatureRequest QgsRelation::getReferencedFeatureRequest ( const QgsAttributes & attributes ) const

Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

Parameters

attributes An attribute vector containing the foreign key

Returns: A request the referenced feature

Definition at line 241 of file qgsrelation.cpp.

◆ getReferencedFeatureRequest() [2/2]

QgsFeatureRequest QgsRelation::getReferencedFeatureRequest ( const QgsFeature & feature ) const

Creates a request to return the feature on the referenced (parent) layer which is referenced by the provided feature.

Parameters

feature A feature from the referencing (child) layer

Returns: A request the referenced feature

Definition at line 269 of file qgsrelation.cpp.

◆ getRelatedFeatures()

QgsFeatureIterator QgsRelation::getRelatedFeatures ( const QgsFeature & feature ) const

Creates an iterator which returns all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

Parameters

feature A feature from the referenced (parent) layer

Returns: An iterator with all the referenced features

See also: getRelatedFeaturesRequest(); getRelatedFeaturesFilter()

Definition at line 190 of file qgsrelation.cpp.

◆ getRelatedFeaturesFilter()

QString QgsRelation::getRelatedFeaturesFilter ( const QgsFeature & feature ) const

Returns a filter expression which returns all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

Parameters

feature A feature from the referenced (parent) layer

Returns: expression filter string for all the referencing features

See also: getRelatedFeatures(); getRelatedFeaturesRequest()

Definition at line 205 of file qgsrelation.cpp.

◆ getRelatedFeaturesRequest()

QgsFeatureRequest QgsRelation::getRelatedFeaturesRequest ( const QgsFeature & feature ) const

Creates a request to return all the features on the referencing (child) layer which have a foreign key pointing to the provided feature.

Parameters

feature A feature from the referenced (parent) layer

Returns: A request for all the referencing features

See also: getRelatedFeatures(); getRelatedFeaturesFilter()

Definition at line 195 of file qgsrelation.cpp.

◆ hasEqualDefinition()

bool QgsRelation::hasEqualDefinition ( const QgsRelation & other ) const

Compares the two QgsRelation, ignoring the name and the ID.

Parameters

other The other relation

Returns: true if they are similar

Definition at line 412 of file qgsrelation.cpp.

◆ id()

QString QgsRelation::id ( ) const

A (project-wide) unique id for this relation.

Returns: The id

Definition at line 293 of file qgsrelation.cpp.

◆ isValid()

bool QgsRelation::isValid ( ) const

Returns the validity of this relation.

Don't use the information if it's not valid. A relation is considered valid if both referenced and referencig layers are valid.

Returns: true if the relation is valid

See also: validationError()

Definition at line 380 of file qgsrelation.cpp.

◆ name()

QString QgsRelation::name ( ) const

Returns a human readable name for this relation.

Mostly used as title for the children.

See also: id()

Returns: A name

Definition at line 283 of file qgsrelation.cpp.

◆ operator=()

QgsRelation & QgsRelation::operator= ( const QgsRelation & other )

Copies a relation.

This makes a shallow copy, relations are implicitly shared and only duplicated when the copy is changed.

Definition at line 48 of file qgsrelation.cpp.

◆ polymorphicRelation()

QgsPolymorphicRelation QgsRelation::polymorphicRelation ( ) const

Returns the parent polymorphic relation.

If the relation is a normal relation, an invalid polymorphic relation is returned.

Since: QGIS 3.18

Definition at line 508 of file qgsrelation.cpp.

◆ polymorphicRelationId()

QString QgsRelation::polymorphicRelationId ( ) const

Returns the parent polymorphic relation id.

If the relation is a normal relation, a null string is returned.

Since: QGIS 3.18

Definition at line 503 of file qgsrelation.cpp.

◆ referencedFields()

QgsAttributeList QgsRelation::referencedFields ( ) const

Returns a list of attributes used to form the referenced fields (most likely primary key) on the referenced (parent) layer.

Returns: A list of attributes

Definition at line 337 of file qgsrelation.cpp.

◆ referencedLayer()

QgsVectorLayer * QgsRelation::referencedLayer ( ) const

Access the referenced (parent) layer.

Returns: referenced layer

Definition at line 327 of file qgsrelation.cpp.

◆ referencedLayerId()

QString QgsRelation::referencedLayerId ( ) const

Access the referenced (parent) layer's id.

Returns: The id of the referenced layer

Definition at line 322 of file qgsrelation.cpp.

◆ referencingFields()

QgsAttributeList QgsRelation::referencingFields ( ) const

Returns a list of attributes used to form the referencing fields (foreign key) on the referencing (child) layer.

Returns: A list of attributes

Definition at line 348 of file qgsrelation.cpp.

◆ referencingFieldsAllowNull()

bool QgsRelation::referencingFieldsAllowNull ( ) const

Returns true if none of the referencing fields has a NOT NULL constraint.

Since: QGIS 3.28

Definition at line 360 of file qgsrelation.cpp.

◆ referencingLayer()

QgsVectorLayer * QgsRelation::referencingLayer ( ) const

Access the referencing (child) layer This is the layer which has the field(s) which point to another layer.

Returns: The referencing layer

Definition at line 317 of file qgsrelation.cpp.

◆ referencingLayerId()

QString QgsRelation::referencingLayerId ( ) const

Access the referencing (child) layer's id This is the layer which has the field(s) which point to another layer.

Returns: The id of the referencing layer

Definition at line 312 of file qgsrelation.cpp.

◆ resolveReferencedField()

QString QgsRelation::resolveReferencedField ( const QString & referencingField ) const

Gets the referenced field counterpart given a referencing field.

Definition at line 417 of file qgsrelation.cpp.

◆ resolveReferencingField()

QString QgsRelation::resolveReferencingField ( const QString & referencedField ) const

Gets the referencing field counterpart given a referenced field.

Definition at line 427 of file qgsrelation.cpp.

◆ setId()

void QgsRelation::setId ( const QString & id )

Set an id for this relation.

Definition at line 139 of file qgsrelation.cpp.

◆ setName()

void QgsRelation::setName ( const QString & name )

Set a name for this relation.

Definition at line 147 of file qgsrelation.cpp.

◆ setPolymorphicRelationId()

void QgsRelation::setPolymorphicRelationId ( const QString & polymorphicRelationId )

Sets the parent polymorphic relation id.

Since: QGIS 3.18

Definition at line 497 of file qgsrelation.cpp.

◆ setReferencedLayer()

void QgsRelation::setReferencedLayer ( const QString & id )

Set the referenced (parent) layer id.

This layer will be searched in the registry.

Definition at line 168 of file qgsrelation.cpp.

◆ setReferencingLayer()

void QgsRelation::setReferencingLayer ( const QString & id )

Set the referencing (child) layer id.

This layer will be searched in the registry.

Definition at line 160 of file qgsrelation.cpp.

◆ setStrength()

void QgsRelation::setStrength ( Qgis::RelationshipStrength strength )

Set a strength for this relation.

Definition at line 154 of file qgsrelation.cpp.

◆ strength()

Qgis::RelationshipStrength QgsRelation::strength ( ) const

Returns the relation strength as a string.

Returns: strength

Definition at line 288 of file qgsrelation.cpp.

◆ strengthToDisplayString()

QString QgsRelation::strengthToDisplayString ( Qgis::RelationshipStrength strength )

static

Returns a user-friendly translated string representing a relationship strength.

Since: QGIS 3.28

Definition at line 540 of file qgsrelation.cpp.

◆ type()

Qgis::RelationshipType QgsRelation::type ( ) const

Returns the type of the relation.

Since: QGIS 3.18

Definition at line 516 of file qgsrelation.cpp.

◆ updateRelationStatus()

void QgsRelation::updateRelationStatus ( )

Updates the validity status of this relation.

Will be called internally whenever a member is changed.

Since: QGIS 3.6

Definition at line 437 of file qgsrelation.cpp.

◆ validationError()

QString QgsRelation::validationError ( ) const

Returns a user-friendly explanation for why the relationship is invalid.

Returns an empty string if the relationship isValid().

See also: isValid()

Since: QGIS 3.28

Definition at line 385 of file qgsrelation.cpp.

◆ writeXml()

void QgsRelation::writeXml	(	QDomNode &	node,
		QDomDocument &	doc
	)		const

Writes a relation to an XML structure.

Used for saving .qgs projects

Parameters

node	The parent node in which the relation will be created
doc	The document in which the relation will be saved

Definition at line 119 of file qgsrelation.cpp.

Property Documentation

◆ id

QString QgsRelation::id

readwrite

Definition at line 47 of file qgsrelation.h.

◆ isValid

bool QgsRelation::isValid

read

Definition at line 51 of file qgsrelation.h.

◆ name

QString QgsRelation::name

readwrite

Definition at line 50 of file qgsrelation.h.

◆ polymorphicRelation

QgsPolymorphicRelation QgsRelation::polymorphicRelation

read

Definition at line 53 of file qgsrelation.h.

◆ polymorphicRelationId

QString QgsRelation::polymorphicRelationId

readwrite

Definition at line 52 of file qgsrelation.h.

◆ referencedLayer

QgsVectorLayer * QgsRelation::referencedLayer

read

Definition at line 49 of file qgsrelation.h.

◆ referencingLayer

QgsVectorLayer * QgsRelation::referencingLayer

read

Definition at line 48 of file qgsrelation.h.

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

/build/qgis-3.41.0+git20241122+3440c17df1d+99sid/src/core/qgsrelation.h
/build/qgis-3.41.0+git20241122+3440c17df1d+99sid/src/core/qgsrelation.cpp

Classes

Public Member Functions

Static Public Member Functions

Properties

Detailed Description

Constructor & Destructor Documentation

◆ QgsRelation() [1/3]

◆ ~QgsRelation()

◆ QgsRelation() [2/3]

◆ QgsRelation() [3/3]

Member Function Documentation

◆ addFieldPair() [1/2]

◆ addFieldPair() [2/2]

◆ cardinalityToDisplayString()

◆ createFromXml()

◆ fieldPairs()

◆ generateId()

◆ getReferencedFeature()

◆ getReferencedFeatureRequest() [1/2]

◆ getReferencedFeatureRequest() [2/2]

◆ getRelatedFeatures()

◆ getRelatedFeaturesFilter()

◆ getRelatedFeaturesRequest()

◆ hasEqualDefinition()

◆ id()

◆ isValid()

◆ name()

◆ operator=()

◆ polymorphicRelation()

◆ polymorphicRelationId()

◆ referencedFields()

◆ referencedLayer()

◆ referencedLayerId()

◆ referencingFields()

◆ referencingFieldsAllowNull()

◆ referencingLayer()

◆ referencingLayerId()

◆ resolveReferencedField()

◆ resolveReferencingField()

◆ setId()

◆ setName()

◆ setPolymorphicRelationId()

◆ setReferencedLayer()

◆ setReferencingLayer()

◆ setStrength()

◆ strength()

◆ strengthToDisplayString()

◆ type()

◆ updateRelationStatus()

◆ validationError()

◆ writeXml()

Property Documentation

◆ id

◆ isValid

◆ name

◆ polymorphicRelation

◆ polymorphicRelationId

◆ referencedLayer

◆ referencingLayer