QgsValueRelationFieldFormatter class

Field formatter for a value relation field.

Reference

A value relation field formatter looks up the values from features on another layer.

Base classes

class QgsFieldFormatter: A field formatter helps to handle and display values for a field.

Public static functions

static auto createCache(const QVariantMap& config, const QgsFeature& formFeature = QgsFeature()) -> QgsValueRelationFieldFormatter::ValueRelationCache: Create a cache for a value relation field.
static auto expressionFormAttributes(const QString& expression) -> QSet<QString>: Returns a list of attributes required by the form context expression.
static auto expressionFormVariables(const QString& expression) -> QSet<QString>: Returns a list of variables required by the form context expression.
static auto expressionIsUsable(const QString& expression, const QgsFeature& feature) -> bool: Check whether the feature has all values required by the expression.
static auto expressionRequiresFormScope(const QString& expression) -> bool: Check if the expression requires a form scope (i.e.
static auto valueToStringList(const QVariant& value) -> QStringList: Utility to convert an array or a string representation of an array value to a string list.

Constructors, destructors, conversion operators

QgsValueRelationFieldFormatter() defaulted: Constructor for QgsValueRelationFieldFormatter.

Public functions

auto createCache(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config) const -> QVariant override: Create a cache for a given field.
auto id() const -> QString override: Returns a unique id for this field formatter.
auto representValue(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config, const QVariant& cache, const QVariant& value) const -> QString override: Create a pretty String representation of the value.
auto sortValue(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config, const QVariant& cache, const QVariant& value) const -> QVariant override: If the default sort order should be overwritten for this widget, you can transform the value in here.

Function documentation

static QgsValueRelationFieldFormatter::ValueRelationCache QgsValueRelationFieldFormatter::createCache(const QVariantMap& config, const QgsFeature& formFeature = QgsFeature())

Create a cache for a value relation field.

Parameters
config	The widget configuration
formFeature	The feature currently being edited with current attribute values
Returns	A kvp list of values for the widget

This can be used to keep the value map in the local memory if doing multiple lookups in a loop.

static QSet<QString> QgsValueRelationFieldFormatter::expressionFormAttributes(const QString& expression)

Returns a list of attributes required by the form context expression.

Parameters
expression	Form filter expression
Returns	list of attributes required by the expression

static QSet<QString> QgsValueRelationFieldFormatter::expressionFormVariables(const QString& expression)

Returns a list of variables required by the form context expression.

Parameters
expression	Form filter expression
Returns	list of variables required by the expression

static bool QgsValueRelationFieldFormatter::expressionIsUsable(const QString& expression, const QgsFeature& feature)

Check whether the feature has all values required by the expression.

Returns	True if the expression can be used

static bool QgsValueRelationFieldFormatter::expressionRequiresFormScope(const QString& expression)

Check if the expression requires a form scope (i.e.

Parameters
expression	The widget's filter expression
Returns	true if the expression requires a form scope

if it uses fields or geometry of the currently edited feature).

static QStringList QgsValueRelationFieldFormatter::valueToStringList(const QVariant& value)

Utility to convert an array or a string representation of an array value to a string list.

QVariant QgsValueRelationFieldFormatter::createCache(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config) const override

Create a cache for a given field.

This will be used in situations where a field is being represented various times in a loop. And will be passed to other methods on QgsFieldKit and QgsEditorWidgetWrapper.

For example, the attribute table will create a cache once for each field and then use this cache for representation. The QgsValueRelationFieldFormatter and QgsValueRelationEditorWidget implement this functionality to create a lookuptable once (a QVariantMap / dict) and are make use of a cache if present.

QString QgsValueRelationFieldFormatter::id() const override

Returns a unique id for this field formatter.

This id will later be used to identify this field formatter in the registry with QgsFieldFormatterRegistry::fieldFormatter().

This id matches the id of a QgsEditorWidgetFactory.

QString QgsValueRelationFieldFormatter::representValue(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config, const QVariant& cache, const QVariant& value) const override

Create a pretty String representation of the value.

Returns	By default the string representation of the provided value as implied by the field definition is returned.

QVariant QgsValueRelationFieldFormatter::sortValue(QgsVectorLayer* layer, int fieldIndex, const QVariantMap& config, const QVariant& cache, const QVariant& value) const override

If the default sort order should be overwritten for this widget, you can transform the value in here.

Returns	an unmodified value by default.