Query codegen

Strawberry supports code generation for GraphQL queries.

Schema codegen will be supported in future releases. We are testing the query codegen in order to come up with a nice API.

Let’s assume we have the following GraphQL schema built with Strawberry:

from typing import List

import strawberry


@strawberry.type
class Post:
    id: strawberry.ID
    title: str


@strawberry.type
class User:
    id: strawberry.ID
    name: str
    email: str

    @strawberry.field
    def post(self) -> Post:
        return Post(id=self.id, title=f"Post for {self.name}")


@strawberry.type
class Query:
    @strawberry.field
    def user(self, info) -> User:
        return User(id=strawberry.ID("1"), name="John", email="abc@bac.com")

    @strawberry.field
    def all_users(self) -> List[User]:
        return [
            User(id=strawberry.ID("1"), name="John", email="abc@bac.com"),
        ]


schema = strawberry.Schema(query=Query)

and we want to generate types based on the following query:

query MyQuery {
  user {
    post {
      title
    }
  }
}

With the following command:

strawberry codegen --schema schema --output-dir ./output -p python query.graphql

We’ll get the following output inside output/types.py:

class MyQueryResultUserPost:
    title: str


class MyQueryResultUser:
    post: MyQueryResultUserPost


class MyQueryResult:
    user: MyQueryResultUser

Why is this useful?

Query code generation is usually used to generate types for clients using your GraphQL APIs.

Tools like GraphQL Codegen exist in order to create types and code for your clients. Strawberry’s codegen feature aims to address the similar problem without needing to install a separate tool.

Plugin system

Strawberry’s codegen supports plugins, in the example above for example, we are using the python plugin. To pass more plugins to the codegen tool, you can use the -p flag, for example:

strawberry codegen --schema schema --output-dir ./output -p python -p typescript query.graphql

the plugin can be specified as a python path.

Custom plugins

The interface for plugins looks like this:

from strawberry.codegen import CodegenPlugin, CodegenFile, CodegenResult
from strawberry.codegen.types import GraphQLType, GraphQLOperation


class QueryCodegenPlugin:
    def on_start(self) -> None:
        ...

    def on_end(self, result: CodegenResult) -> None:
        ...

    def generate_code(
        self, types: List[GraphQLType], operation: GraphQLOperation
    ) -> List[CodegenFile]:
        return []

• on_start is called before the codegen starts.

• on_end is called after the codegen ends and it receives the result of the codegen. You can use this to format code, or add licenses to files and so on.

• generated_code is called when the codegen starts and it receives the types and the operation. You cans use this to generate code for each type and operation.