Field validation

Individual fields

Before the mutation is executed, the value of each field is validated. By default, each field passes this validation process. Custom validation can be added per field by adding a validate_<fieldname>-method to the mutation class.

nordic_names = ["Odin", "Tor", "Balder"]

class CreateUserMutation(DjangoCreateMutation):
    class Meta:
        model = User

    def validate_first_name(root, info, value, input, **kwargs):
        if not value in nordic_names:
            raise ValueError("First name must be nordic")

Raise an error if a field does not pass validation.

A field validation function always receives the arguments (root, info, value, input). For some mutations, extra keyword arguments are also supplied:

• DjangoUpdateMutation and DjangoPatchMutation: obj, the retrieved model instance, and id the input id.
• DjangoBatchCreateMutation: full_input, the full input object (i.e. containing all objects to be created).

Overriding the validation pipeline

Internally, each mutation calls a method named validate, which in turn finds the individual field validation methods on the class, and calls these.

You can, however, override this validate function, if you need a more complex validation pipeline.

class UpdateUserMutation(DjangoUpdateMutation):
    class Meta:
        model = User

    @classmethod
    def validate_first_name(cls, root, info, value, input, **kwargs):
        if not value in nordic_names:
            raise ValueError("First name must be nordic")

    @classmethod
    def validate(cls, root, info, input, obj=None, id=None):
        # Check that the user being updated is active
        if obj and obj.is_active == False:
            raise ValueError("Inactive users cannot be updated")

        super().validate(root, info, input, obj=obj, id=id)

The validate method takes the same arguments as the individual validate_field methods, minus the value field.

Known limitations

There is currently no way to explicitly validate nested fields, beyond validating the entire field substructure. I.e. for a deeply nested field named enemies, the only way to validate this field and its “sub”-fields, is by having a method validate_enemies.