Class: QgsDefaultValue¶

class qgis.core.QgsDefaultValue(expression: str = '', applyOnUpdate: bool = False)¶

Bases: sip.wrapper

Create a new default value with the given expression and applyOnUpdate flag.

QgsDefaultValue(QgsDefaultValue)

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

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: Enums

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.

Signals

Attributes

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.

expression(self) → str¶: The expression will be evaluated whenever a default value needs to be calculated for a field.

isValid(self) → bool¶

Returns if this default value should be applied.

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.

setExpression(self, expression: str)¶: The expression will be evaluated whenever a default value needs to be calculated for a field.