Setting a field constraint using PyQGIS

Question

I am trying to set a field constraint for a specific field called 'node_id' for node layer. Below is the code:

layer = iface.activeLayer()
field_index = layer.fields().indexFromName("node_id")
constraint_expression = '"node_id"==0 or "node_id" == 1'
layer.setFieldConstraint(field_index, QgsFieldConstraints.Constraint(constraint_expression))
layer.updateFields()

I am facing this error:

ValueError: invalid literal for int() with base 10: '"node_id" not NULL'

Answer 1

Want to improve this post? Provide detailed answers to this question, including citations and an explanation of why your answer is correct. Answers without enough detail may be edited or deleted.

layer.setFieldConstraint(field_index, QgsFieldConstraints.ConstraintExpression)
layer.setConstraintExpression(field_index, '"node_id" in (0, 1)')

• BenStone: I want to set an expression like - 'node_id' ==1 or 0 no other value. So thats why I need expression @RainForest
• BenStone: I have edited the expression, need to set the expression for the specific field - Node id should have value 0 or 1.
• BenStone: Thank you , this works
• BenStone: One small question: Is there any way to add a tooltip/placeholder for a field using pyqgis?
• RainForest: layer.setFieldAlias(field_index, 'This Field Alias')