Dynamically creating graphql schema with circular references - graphql

Question

By using graphql-js, I need to create graphql schema dynamically by iterating over array of some data, for example:
[{
name: 'author',
fields: [{
field: 'name'
}, {
field: 'books',
reference: 'book'
}]
}, {
name: 'book',
fields: [{
field: 'title'
}, {
field: 'author',
reference: 'author'
}]
}]
The problem is circular references. When I'm creating AuthorType I need BookType to be already created and vise versa.
So resulting schema should look like:
type Author : Object {
id: ID!
name: String,
books: [Book]
}
type Book : Object {
id: ID!
title: String
author: Author
}
How can I solve this?

Answer 1

Quoted from official documentation
http://graphql.org/docs/api-reference-type-system/
When two types need to refer to each other, or a type needs to refer
to itself in a field, you can use a function expression (aka a closure
or a thunk) to supply the fields lazily.
var AddressType = new GraphQLObjectType({
name: 'Address',
fields: {
street: { type: GraphQLString },
number: { type: GraphQLInt },
formatted: {
type: GraphQLString,
resolve(obj) {
return obj.number + ' ' + obj.street
}
}
}
});
var PersonType = new GraphQLObjectType({
name: 'Person',
fields: () => ({
name: { type: GraphQLString },
bestFriend: { type: PersonType },
})
});
Also look at this related answer of circular Category-Subcategory types

Answer 2

I solved this problem by using a thunk for the fields field.
const User = new GraphQLObjectType({
name: 'User',
fields: () => ({
id: { type: GraphQLID }
})
});
When you make your fields a thunk rather than an object literal you can use types that are defined later in the file.
Please see this post for more info Is there a way to avoid circular type dependencies in GraqhQL?
Based on that post I think this is the correct way to do it.