如何以编程方式定义递归GraphQL类型？

Question

Let's say, for example, I want to define a typical forum message type using GraphQL JavaScript interface:

import {
  GraphQLString,
  GraphQLObjectType,
} from 'graphql';

const MessageType = new GraphQLObjectType({
  name: 'Message',
  fields: {
    text: { type: GraphQLString },
    comments: new GraphQLList(MessageType),
  },
});

The JavaScript compiler (well, interpreter) would complain about this. It would say that MessageType is undefined .

We all know it is possible to define such a type using the GraphQL language:

type Message {
    text: String
    comments: [Message]
}

How could you define such a type using GraphQL pure JavaScript interface?

Answer 1

Well, the answer is simple.

You just need to pass a thunk (function without arguments) as the field field instead of passing plain JavaScript object.

The function would be executed only when the type would already be defined, so, it will work.

Resulting code looks like this:

import {
  GraphQLString,
  GraphQLObjectType,
} from 'graphql';

const MessageType = new GraphQLObjectType({
  name: 'Message',
  fields: () => ({  // <-- Notice the function definition
    text: { type: GraphQLString },
    comments: new GraphQLList(MessageType),
  }),
});