Class: QgsDefaultValue

class qgis.core.QgsDefaultValue

Bases: sip.wrapper

The QgsDefaultValue class provides a container for managing client side default values for fields.

A QgsDefaultValue consists of an expression string that will be evaluated on the client when a default field value needs to be generated.

Usual values for such an expression are

  • :py:func:`~now` for a timestamp for a record

  • @some_variable to insert a project or application level variable like the username of the one digitizing a feature

  • $length to insert a derived attribute of a geometry

QgsDefaultValue also has a applyOnUpdate flag which will indicate that a default value should also be applied when a feature is updated. If this is not set, the default value will only be used when a feature is created.

New in version 3.0.

QgsDefaultValue(expression: str = ‘’, applyOnUpdate: bool = False) Create a new default value with the given expression and applyOnUpdate flag.

QgsDefaultValue(QgsDefaultValue)

Methods

applyOnUpdate

The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.

expression

The expression will be evaluated whenever a default value needs to be calculated for a field.

isValid

Returns if this default value should be applied.

setApplyOnUpdate

The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.

setExpression

The expression will be evaluated whenever a default value needs to be calculated for a field.

applyOnUpdate(self)bool

The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.

Return type

bool

expression(self)str

The expression will be evaluated whenever a default value needs to be calculated for a field.

Return type

str

isValid(self)bool

Returns if this default value should be applied.

Return type

bool

Returns

False if the expression is a null string.

setApplyOnUpdate(self, applyOnUpdate: bool)

The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.

Parameters

applyOnUpdate (bool) –

setExpression(self, expression: str)

The expression will be evaluated whenever a default value needs to be calculated for a field.

Parameters

expression (str) –