[GraphQL] Add an Interface to a GraphQL Schema

As we start building out more complex GraphQL schemas, certain fields start to repeat across different types. This is a perfect use-case for the Interface Type made available to us through GraphQL’s Type System. In this video, we’ll go over how to create an Interface Type and how to add it to an existing type in a GraphQL Schema.

Add an interface for video ID:

const {
          GraphQLInterfaceType, GraphQLNonNull, GraphQLID
      }             = require('graphql');
const { videoType } = require('../schema');

const IDInterface = new GraphQLInterfaceType({
    name        : 'IDNode',
    fields      : {
        id : {
            type : new GraphQLNonNull(GraphQLID)
        }
    },
    resolveType : (object) => {
        if( object.title ) {
            return videoType;
        }

        return null;
    }
});

module.exports = IDInterface;

Add interface for query:

const express     = require('express');
const graphqlHttp = require('express-graphql');
const {
          getVideoById, getVideos, createVideo
      }           = require('./data/index');
const IDInterface = require('./interfaces/index');
const server      = express();
const port        = process.env.PORT || 3000;

const {
          GraphQLSchema, GraphQLObjectType, GraphQLInputObjectType, GraphQLString, GraphQLList, GraphQLInt, GraphQLNonNull, GraphQLBoolean, GraphQLID
      } = require('graphql');

const videoType = new GraphQLObjectType({
    name        : 'video',
    description : 'A video on Egghead.io',
    fields      : {
        id       : {
            type        : new GraphQLNonNull(GraphQLID),
            description : 'The id of the video'
        },
        title    : {
            type        : GraphQLString,
            description : 'The title of the video'
        },
        duration : {
            type        : GraphQLInt,
            description : 'The duration of the video'
        },
        watched  : {
            type        : GraphQLBoolean,
            description : 'Whether or no the viewer watched the video'
        }
    },
    interfaces: [IDInterface]
});
exports.videoType = videoType;

const videoInputType = new GraphQLInputObjectType({
    name   : 'videoInput',
    fields : {
        title    : {
            type        : new GraphQLNonNull(GraphQLID),
            description : 'The title of the video'
        },
        duration : {
            type        : new GraphQLNonNull(GraphQLInt),
            description : 'The duration of the video'
        },
        watched  : {
            type : new GraphQLNonNull(GraphQLBoolean)
        }
    }
});

const mutationType = new GraphQLObjectType({
    name        : 'Mutation',
    description : 'The root Mutation type',
    fields      : {
        createVideo : {
            type    : videoType,
            args    : {
                video : {
                    type : new GraphQLNonNull(videoInputType),
                },
            },
            resolve : (_, args) => {
                return createVideo(args.video)
            }
        }
    }
});

const queryType = new GraphQLObjectType({
    name        : 'QueryType',
    description : 'The root query type',
    fields      : {
        videos : {
            type    : new GraphQLList(videoType),
            resolve : getVideos
        },
        video  : {
            type    : videoType,
            args    : {
                id : {
                    type        : new GraphQLNonNull(GraphQLID),
                    description : 'The id of the video'
                }
            },
            resolve : (_, args) => getVideoById(args.id)
        }
    }
});

const schema = new GraphQLSchema({
    query    : queryType,
    mutation : mutationType
});

server.use('/graphql', graphqlHttp({
                                       schema,
                                       graphiql : true, // use graphiql interface
                                   }));

server.listen(port, () => {
    console.log(`Listening on http`)
})