Handling Mongoose Populated Fields in GraphQL

Question

How do I represent a field that could be either a simple ObjectId string or a populated Object Entity?

I have a Mongoose Schema that represents a \'Device t

Answer 1

As a matter of fact, you can use union or interface type for linked_device field.

Using union type, you can implement GQAssetType as follows:

// graphql-asset-type.js

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

var LinkedDeviceType = new GraphQLUnionType({
  name: 'Linked Device',
  types: [ ObjectIdType, GQAssetType ],
  resolveType(value) {
    if (value instanceof ObjectId) {
      return ObjectIdType;
    }
    if (value instanceof Asset) {
      return GQAssetType;
    }
  }
});

export var GQAssetType = new GraphQLObjectType({
  name: 'Asset',
  fields: () => ({
    name: { type: GraphQLString },
    linked_device: { type: LinkedDeviceType },
  })
});

Check out this excellent article on GraphQL union and interface.