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
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
andapplyOnUpdate
flag.QgsDefaultValue(
QgsDefaultValue
)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) –