Errors design

[lorddaedra]

Let's assume, we use this schema. We have users and projects. Just after login we make me query and load some data, related with user and his(her) projects.

type Query {
    me: UserResponse!
}

type Error {
    code: Int!
    message: String!
}

type OperationError {
    errors: [Error!]!
}

type User {
    name: ID!
    email: String!
    projects: [Project!]!
}

type Project {
    name: ID!
    display_name: String!
}

union UserResponse = User | OperationError

Our query:

import {gql} from 'graphql-tag';

const ME = gql`
    query Me {
        me {
            ... on User {
                name
                email
                projects {
                    name
                    display_name
                }
            }
            ... on OperationError {
                errors {
                    code
                    message
                }
            }
        }
    }
`;

export {ME};

and on server side we have simple resolver like that:

def resolve_me(obj: Any, info: GraphQLResolveInfo) -> Mapping[str, Union[str, Sequence]]:
    user: User = info.context["request"].user

    # Login only
    if user.is_anonymous:
        return {'__typename': 'OperationError', 'errors': [{'code': HTTPStatus.UNAUTHORIZED, 'message': 'Login required'}]}

    projects_data: Sequence[Mapping] = ProjectInterface.list_projects(user_name=user.name)  # load some data from internal API of another app (Django API Domains style)

    # Require at least one project
    if not projects_data:
        return {'__typename': 'OperationError', 'errors': [{'code': HTTPStatus.INTERNAL_SERVER_ERROR, 'message': 'Please, contact support...'}]}

    return {
        '__typename': 'User',
        'name': str(user.name),
        'email': user.email,
        'projects': [
            project_data | {'__typename': 'Project'} for project_data in projects_data
        ]
    }

Let's assume, we have projects field somewhere else and now we would like refactor and add separate resolve_projects resolver.

Questions:

1. Is it good idea to keep all errors only on root level (inside 'data')? I think, answer is 'yes' because of it will simplify error handling a lot.

2. How to deal with OperationError in this case, how to move error from resolve_projects to top level of 'data' output (to top parent resolver, resolve_me or anything else)?