GraphQL relationship returning null

Question

I'm learning graphql and working on a simple API with mongodb database. I can't figure out why the relationship declared in my schema is not working :

type People {
    id:ID!
    firstName:String!
    lastName:String!
    email:String!
    serviceId:String
    apps:[String]
    service:Service
}
type Service {
    id:ID!
    name:String!
    location:String!
    peoples:[People]
}

When I run this query:

query getLocationByPerson {
   People {
      firstName
      lastName
      service {
        location
      }
   }
}

Here's what I get:

"People": [
      {
        "firstName": "John",
        "lastName": "DOE",
        "service": null
      },
      {
        "firstName": "Jane",
        "lastName": "DOE",
        "service": null
      }
]

Any idea of what I'm missing here?

all the code is here : github.com/fabricezerrouki/graphql-playground thx — user3414794
– user3414794, Commented Feb 18, 2019 at 15:51

Ric0 · Accepted Answer · 2019-02-19 17:59:41Z

0

The issue lays in your resolvers:

Based on the repo you linked your queries look like the following:

const People = require('../database/people');
const Service = require('../database/service');
const queries = {
    People: () => People.find({}),
    ...
    Service: () => Service.find({}),
    ...
  };

module.exports = queries;

The People schema looks like this:

const mongoose = require('mongoose');

const Schema = mongoose.Schema;
const peopleSchema = new Schema({
    Xid: { type: String },
    firstName: { type: String },
    lastName: { type: String },
    email: { type: String },
    apps: { type: Array },
    serviceId: { type: String },
    service: { type: Schema.Types.ObjectId, ref: 'service' }
},{ versionKey: false })

module.exports = mongoose.model('people', peopleSchema);

People.find() will return only the service _id though not the whole service object. That is why you get null in the response.

The GraphQL relationship you implemented in People has a Service Type while you're getting back from the db only the service _id.

You have 2 solutions:

A) You want to retrieve the Service object as well when you query for People. In this case you need to use the mongoose populate function: People: () => People.find({}).populate('service'),

The above will provide People with the referenced Service object (not just the _id)

Because you're using id instead of _id in your schema the above is not enough and you need to use the following instead where you also create an id field to return for each service

People: async () => {
      const people = await People.find({}).populate('service').exec()
      return people.map(person => ({
        ...person._doc,
        id: person._doc._id,
        service: {
          ...person._doc.service._doc,
          id: person._doc.service._doc._id,
        },
      }))
    }, return people
}

The above is quite convulted. I'd strongly suggest going with solution (B)

Docs about populate(): https://mongoosejs.com/docs/populate.html

B) User a type resolver

// Type.js
const Service = require('../database/service');
const types = {
    People: {
      // you're basically saying: In People get service field and return...
      service: ({ service }) => Service.findById(service), // service in the deconstructed params is just an id coming from the db. This param comes from the `parent` that is People
    },
   Service: {
     id: ({_id}) => _id, // because you're using id in your schema
},
  };

module.exports = queries;

A note on the implementation of this option:

it is my preferred one although you'll eventually need a dataloader to batch calls to the db, otherwise it will be very inefficient. Basically you need solving the N+1 problem and ensuring your db is queried efficiently. Here there is a very good article about it: http://www.petecorey.com/blog/2017/08/14/batching-graphql-queries-with-dataloader/?from=east5th.co

edited Feb 19, 2019 at 17:59

answered Feb 19, 2019 at 9:26

Ric0

6501 gold badge6 silver badges11 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

user3414794 Over a year ago

thanks for your help. I tried the A) solution but im still getting null result for the location field. And the following error: `` Error: Cannot return null for non-nullable field Service.location. ``

Ric0 Over a year ago

That is probably because you have id: ID! in your type Service while _id is, I guess, coming back from the db. As I guess you do not want to use the type resolver option for the field id as well I'm editing my answer to fix that error

user3414794 Over a year ago

Thanks again. I'm new to node.js, graphql & mongodb so I'm probably not implementing your solutions properly because I still get the null result. Would you mind to create a pull request in my repo please?

Ric0 Over a year ago

Please add first the package.json to your repo.

Ric0 Over a year ago

Looking more deeply in your code I am afraid you might not store data as it should be in the first place. Can you add to your repo an actual sample object coming from your db for both one People and the related Service?

|

Collectives™ on Stack Overflow

GraphQL relationship returning null

1 Answer 1

10 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

10 Comments

Your Answer

Sign up or log in

Post as a guest

Related