GraphQL "Cannot return null for non-nullable"

Question

Trying to make my first graphQL server, here's what I have written so far.

https://gist.github.com/tharakabimal/7f2947e805e69f67af2b633268db0406

Following error pops up on GraphQL when I try to filter the users by username.

The error occurs in the users field in UserQueriesQL.js.

Is there anything wrong the way I pass arguments on the resolve functions?

user: {
type: UserType,
args: { 
  username: {
    name: 'username',
    type: new GraphQLNonNull(GraphQLString)
  }
},
resolve: function(parentValue, args) {
  return User.find( args ).exec();
}

The error means you are returning `null`, but with `type: new GraphQLNonNull(GraphQLString)` you declared that there may never be returned `null` for the username. Either return something else than `null`, or declare the type as `type: new GraphQLString()` — marktani, Feb 23 '17 at 13:49
`User.find` will resolve to an array, but GraphQL is expecting an object instead. Please see Common Scenario #2 in [this answer](https://stackoverflow.com/questions/56319137/why-does-a-graphql-query-return-null/56319138#56319138). — Daniel Rearden, Jun 01 '19 at 16:24

score 6 · Answer 1 · answered Mar 29 '19 at 13:56

As I am beginner into GraphQL, even I ran into this issue. After going through each file individually I found that I forgot to import into my resolvers

import User from './User';
**import Post from './Post';**

const resolvers = [User, **Posts**];

Maybe this will help!

parwatcodes · Answer 2 · 2017-02-23T11:30:59.543

1

user: {
type: UserType,
args: { 
  username: { type: new GraphQLNonNull(GraphQLString) }
},
resolve: function(parentValue, args) {
  return User.find( args ).exec(); // User.find({username: 'some name'}).exec(); 
// will work as matches your mongoose schema
}

Previously, in the args you are providing an an object with nested object username so,

args: {  // this won't match your mongoose schema field as it's nested object
  username: {
    name: 'username',
    type: new GraphQLNonNull(GraphQLString)
  }
}

so when the user queries and provides args then your args would be { username: { name: 'abcd' } }

// args = {username: {name: 'abcd'}}

and resolve() is executing User.find({username: {name: 'abcd'}}).exec();

/* searching for username{} object, but
your mongoose schema is username: String */

which doesn't match your database fields, which will always return an empty array [],also which will not match your GraphQL field type, as it is GraphQLNonNull

after viewing the gist the problem is with rootquery

the problem is with rootquery

let RootQuery = new GraphQLObjectType({
    name: 'RootQueryType',
    fields: () => ({
        users: { type:UserQueries.users, resolve: UserQueries.users }
        user: { type: UserQueries.user, resolve: UserQueries.user }
    })
});

edited Feb 23 '17 at 11:30

answered Feb 23 '17 at 07:05

parwatcodes

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I did the suggested changes, but still having the issue https://gist.github.com/tharakabimal/c84ff21d6a6aa898cb3ccc02757867df – King Julian Feb 23 '17 at 10:35
have you entered the username in the args – parwatcodes Feb 23 '17 at 10:37
Yes https://gist.github.com/tharakabimal/1883dcb50322456fe81d37e9abc22daa – King Julian Feb 23 '17 at 10:55
so do you have username `John` in `users` collection, put a gist and snapshot of the database – parwatcodes Feb 23 '17 at 10:58
Here are the 3 users I have in my mongoDB https://gist.github.com/tharakabimal/cdd58e7534fef268801142eb7ce4266c – King Julian Feb 23 '17 at 11:09
the problem is with the rootQuery – parwatcodes Feb 23 '17 at 11:23

GraphQL "Cannot return null for non-nullable"

2 Answers2