Using the Schema Definition LanguageΒΆ

Above we defined the GraphQL schema as Python code, using the GraphQLSchema class and other classes representing the various GraphQL types.

GraphQL-core 3 also provides a language-agnostic way of defining a GraphQL schema using the GraphQL schema definition language (SDL) which is also part of the GraphQL specification. To do this, we simply feed the SDL as a string to the graphql.utilities.build_schema() function:

from graphql import build_schema

schema = build_schema("""

    enum Episode { NEWHOPE, EMPIRE, JEDI }

    interface Character {
      id: String!
      name: String
      friends: [Character]
      appearsIn: [Episode]
    }

    type Human implements Character {
      id: String!
      name: String
      friends: [Character]
      appearsIn: [Episode]
      homePlanet: String
    }

    type Droid implements Character {
      id: String!
      name: String
      friends: [Character]
      appearsIn: [Episode]
      primaryFunction: String
    }

    type Query {
      hero(episode: Episode): Character
      human(id: String!): Human
      droid(id: String!): Droid
    }
    """)

The result is a GraphQLSchema object just like the one we defined above, except for the resolver functions which cannot be defined in the SDL.

We would need to manually attach these functions to the schema, like so:

schema.query_type.fields['hero'].resolve = get_hero
schema.get_type('Character').resolve_type = get_character_type

Another problem is that the SDL does not define the server side values of the Episode enum type which are returned by the resolver functions and which are different from the names used for the episode.

So we would also need to manually define these values, like so:

for name, value in schema.get_type('Episode').values.items():
    value.value = EpisodeEnum[name].value

This would allow us to query the schema built from SDL just like the manually assembled schema:

from graphql import graphql_sync

result = graphql_sync(schema, """
    {
      hero(episode: EMPIRE) {
        name
        appearsIn
      }
    }
    """)
print(result)

And we would get the expected result:

ExecutionResult(
    data={'hero': {'name': 'Luke Skywalker',
                   'appearsIn': ['NEWHOPE', 'EMPIRE', 'JEDI']}},
    errors=None)