Custom errors management with partial results

[tvallois]

Hello,

I don't know if the question has already been asked/answered, i don't find any traces of it.
I try to follow GraphQL specs to manage errors with our application.
Imagine a scenario where i try to create 3 tokens linked to emails using a mutation:

type Mutation {
    createTokens(
         emails: [String!]!
    ): CreateTokensPayload!
}

type Token {
   data: String!
   email: String!
}

type CreateTokensPayload {
    tokens: [Token]
}

If everything work fine, i should have this result:

{
  "data": {
    "createTokens": [
      {
        "data": "sze",
        "email": "email1@gmail.com"
      },
      {
        "data": "azead",
        "email": "email2@gmail.com"
      },
      {
        "data": "adzadzd",
        "email": "email3@gmail.com"
      }
    ]
  }
}

If an error occur only on email email2@gmail.com, according to GraphQL specs, i should have this kind of result:

{
  "errors": [
    {
      "message": "error message",
      "locations": [
        {
          "line": 6,
          "column": 7
        }
      ],
      "path": [
        "createTokens",
        1,
        "email"
      ]
    }
  ],
  "data": {
    "createTokens": [
      {
        "data": "sze",
        "email": "email1@gmail.com"
      },
      null,
      {
        "data": "adzadzd",
        "email": "email3@gmail.com"
      }
    ]
  }
}

I don't find a way to do this with Ariadne, any suggestions?

Thanks!

[rafalp]

The part of errors spec you are referring to is about errors during data retrieval. This means that error for invalid e-mail should be raised in resolver for Token's email field.

For example you createTokens mutation could return this data:

{
    "tokens": [
        {"data": "valid data", "email": "valid@example.com", "error": None},
        {"data": "valid data", "email": None, "error": "Invalid email!"},
        {"data": "valid data", "email": "valid2@example.com", "error": None},
    ]
}

With email resolver like this:

def resolve_email(obj, *_):
    if obj.get("error"):
        raise ValueError(obj["error"])

    return obj["email"]

[rafalp]

No, it's not. Both Ariadne and Apollo behave the same in this field. But Apollo documentation suggests you to extend the spec for reporting errors specific to the application, and Ariadne tells you to define custom error types that are part of schema for the same.

I'll explain this in more detail now, but key difference between what you are trying to accomplish and what Apollo shows, is that you are trying to return error for a sub field in GraphQL type resulted by mutation, and their example returns an error from top level field in query.

In their example field they want to return error for is the same field that that implements logic, the userWithID field. In your example logic lives in the createTokens field, but you want those errors come from individual email fields belonging to the Token type which is returned from tokens field belonging to CreateTokensPayload.

So you need to first pass your error down to the email field before it can be raised. If you were using Apollo server (or any other spec compliant server), it will be exactly the same. You would have to pass the information about the error down to an email field.

---

I've just remembered that part of GraphQL spec is that if resolver field returns error (not raises but returns), query executor should treat this situation the same to error being raised from resolver. So you could skip custom email resolver and return data from createTokens that looks like this:

{
    "tokens": [
        {"data": "valid data", "email": "valid@example.com", "error": None},
        {"data": "valid data", "email": ValueError("Invalid email!")},
        {"data": "valid data", "email": "valid2@example.com", "error": None},
    ]
}

[tvallois]

I'm not sure to fully understand your explanation.
I tried to do something like this:

from ariadne import MutationType

def create_tokens(*_, emails):
    tokens = [{"token": "fsqd", "email": ValueError("boom"), {"token": "aze", "email": emails[0]}}]
    return invalid_tokens

mutation_type = MutationType()
mutation_type.set_field("createTokens", create_tokens)

This solution return:

{'data': {'createTokens': {'tokens': None}}, 'errors': [{'message': 'boom', 'locations': [{'line': 14, 'column': 21}], 'path': ['createTokens', 'tokens', 0, 'email']}]}

[rafalp]

tokens = [{"token": "fsqd", "email": ValueError("boom"), {"token": "aze", "email": emails[0]}}]
return invalid_tokens

Why are you defining tokens but returning invalid_tokens which is undefined? 🤔 Also your schema defines tokens field, but your resolver is not returning value for it. Shouldn't it be:

def create_tokens(*_, emails):
    tokens = [{"token": "fsqd", "email": ValueError("boom"), {"token": "aze", "email": emails[0]}}]
    return {"tokens": tokens}

?

[tvallois]

My test was bad sorry.

Ok your suggestion seems to work as i want:

# Mutation
def create_tokens(*_, emails):
    valid_tokens = [{"data": "aze", "email": email} for email in emails]
    invalid_tokens = [{"data": "fsqd", "email": ValueError("boom")}]
    invalid_tokens.extend(valid_tokens)
    return {"tokens": invalid_tokens}
​
​
mutation_type.set_field("createTokens", create_tokens)

# Test
@pytest.mark.asyncio
async def test_error():
    async with AsyncClient(app=app, base_url="http://localhost") as ac:
        mut = """
        mutation createTokens(
            $emails: [String!]!
        ) {
            createTokens(
                emails: $emails,
            ) {
                tokens {
                    data
                    email
                }
            }
        }
    """
        response = await ac.post(
            "/graphql/",
            json={
                "query": mut,
                "variables": {"emails": ["aze", "eza"]},
            },
        )
        assert response.status_code == 200
        assert response.json() == {'data': {'createTokens': {'tokens': [None, {'data': 'aze', 'email': 'aze'}, {'data': 'aze', 'email': 'eza'}]}}, 'errors': [{'message': 'boom', 'locations': [{'line': 10, 'column': 21}], 'path': ['createTokens', 'tokens', 0, 'email']}]}

[tvallois]

Thanks for your help !