Class: QgsDefaultValue¶
- class qgis.core.QgsDefaultValue(expression: str = '', applyOnUpdate: bool = False)¶
Bases:
sip.wrapper
Create a new default value with the given
expression
andapplyOnUpdate
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
: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.Methods
The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.
The expression will be evaluated whenever a default value needs to be calculated for a field.
Returns if this default value should be applied.
The applyOnUpdate flag determines if this expression should also be applied when a feature is updated or only when it’s created.
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) –