This example project outlines and tests a proposed interface for a validation style for Graphene.

An example implementation that supports this example can be found here.

Validators can be specified on any InputObjectType as seen in this relevant snippet:

class UserInput(graphene.InputObjectType):
    username = graphene.String()
    password = graphene.String()

    def validate_password(self, password):
        if not password or len(password) < 8:
            raise GraphQLError('Please enter a password at least eight characters long')

Why?

This approach co-locates input shapes with their appropriate validation and discourages repeated logic (and minimises forgotten validation steps within mutation functions).

Why not?

The existing feature set of Graphene is tightly coupled to GraphQL, with an obvious 1-to-1 mapping from the Graphene schema to the resulting core GraphQL schema. This validation interface is in no way standard to Graphene and such non-standard approaches have downsides:

1. They can mislead newcomers to the GraphQL ecosystem by blurring the line between GraphQL specification, and implementations of the GraphQL specification like Graphene.
2. They open the door to further deviation from the GraphQL specs, raising the question of where to draw the line.

Running

1. Clone this repo.
2. Create a virtualenv: python3 -m venv venv
3. Source the virtualenv: source venv/bin/activate
4. Run the tests: python -m unittest