GraphQL - How to respond with different status code?

Question

I'm having a trouble with Graphql and Apollo Client.

I always created different responses like 401 code when using REST but here I don't know how to do a similar behavior.

When I get the response, I want it to go to the catch function. An example of my front-end code:

client.query({
  query: gql`
    query TodoApp {
      todos {
        id
        text
        completed
      }
    }
  `,
})
  .then(data => console.log(data))
  .catch(error => console.error(error));

Can anybody help me?

Answer 1

The way to return errors in GraphQL (at least in graphql-js) is to throw errors inside the resolve functions. Because HTTP status codes are specific to the HTTP transport and GraphQL doesn't care about the transport, there's no way for you to set the status code there. What you can do instead is throw a specific error inside your resolve function:

age: (person, args) => {
  try {
    return fetchAge(person.id);
  } catch (e) {
    throw new Error("Could not connect to age service");
  }
}

GraphQL errors get sent to the client in the response like so:

{
  "data": {
    "name": "John",
    "age": null
  },
  "errors": [
    { "message": "Could not connect to age service" }
  ]
}

If the message is not enough information, you could create a special error class for your GraphQL server which includes a status code. To make sure that status code gets included in your response, you'll have to specify the formatError function when creating the middleware:

app.use('/graphql', bodyParser.json(), graphqlExpress({ 
    schema: myGraphQLSchema,
    formatError: (err) => ({ message: err.message, status: err.status }),
}));

Answer 2

There has been a recent addition to the spec concerning errors outputs:

GraphQL services may provide an additional entry to errors with key extensions. This entry, if set, must have a map as its value. This entry is reserved for implementors to add additional information to errors however they see fit, and there are no additional restrictions on its contents.

Now using the extensions field you can custom machine-readable information to your errors entries:

{
  "errors": [
    {
      "message": "Name for character with ID 1002 could not be fetched.",
      "locations": [ { "line": 6, "column": 7 } ],
      "path": [ "hero", "heroFriends", 1, "name" ],
      "extensions": {
        "code": "CAN_NOT_FETCH_BY_ID",
        "timestamp": "Fri Feb 9 14:33:09 UTC 2018"
      }
    }
  ]
}

Latest version of Apollo-Server is spec-compliant with this feature check it out, Error Handling.