Build an App

Goals

On this page, you will learn how to:

• Define a GraphQL schema for your GraphQL server
• Implement resolver functions using the Prisma client
• Use the GraphQL Playground to try out your GraphQL API

Configure Project

grahpql-yoga is a GraphQL server library based on Express.js. Add it to your project with the following command:

npm install --save graphql-yoga
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Define GraphQL API

Every GraphQL API is based on a GraphQL schema that specifies all API operations and data structures. The schema is as a contract between client and server.

Create a new file called schema.graphql:

touch schema.graphql
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To define the API operations, you need to specify the Query and Mutation types in your GraphQL schema - the following operations are examples for a simple blogging application:

type Query {
  publishedPosts: [Post!]!
  post(postId: ID!): Post
  postsByUser(userId: ID!): [Post!]!
}

type Mutation {
  createUser(name: String!): User
  createDraft(title: String!, userId: ID!): Post
  publish(postId: ID!): Post
}

type User {
  id: ID!
  email: String
  name: String!
  posts: [Post!]!
}

type Post {
  id: ID!
  title: String!
  published: Boolean!
  author: User
}
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The Post and User types are straightforward re-definitions of the models specified in datamodel.prisma, except that the Prisma-specific directives have been removed.

Implement resolver functions

Here is how you implement the resolver functions for the six API operations defined in the GraphQL schema. Replace the current contents of index.ts entirely with the following code snippet:

import { prisma } from './generated/prisma-client'
import { GraphQLServer } from 'graphql-yoga'

const resolvers = {
  Query: {
    publishedPosts(parent, args, context) {
      return context.prisma.posts({ where: { published: true } })
    },
    post(parent, args, context) {
      return context.prisma.post({ id: args.postId })
    },
    postsByUser(parent, args, context) {
      return context.prisma
        .user({
          id: args.userId,
        })
        .posts()
    },
  },
  Mutation: {
    createDraft(parent, args, context) {
      return context.prisma.createPost({
        title: args.title,
        author: {
          connect: { id: args.userId },
        },
      })
    },
    publish(parent, args, context) {
      return context.prisma.updatePost({
        where: { id: args.postId },
        data: { published: true },
      })
    },
    createUser(parent, args, context) {
      return context.prisma.createUser({ name: args.name })
    },
  },
  User: {
    posts(parent, args, context) {
      return context.prisma
        .user({
          id: parent.id,
        })
        .posts()
    },
  },
  Post: {
    author(parent, args, context) {
      return context.prisma
        .post({
          id: parent.id,
        })
        .author()
    },
  },
}
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Each resolver invokes a method on the Prisma client instance which is called prisma and attached to the context object.

Configure your GraphQL server

Now you need to instantiate the GraphQLServer from the graphql-yoga library and pass the GraphQL schema along with its resolver functions. You're also attaching the imported prisma client instance to the context so that the resolvers can access it.

Add the following code snippet to the bottom of index.ts:

const server = new GraphQLServer({
  typeDefs: './schema.graphql',
  resolvers,
  context: {
    prisma,
  },
})
server.start(() => console.log('Server is running on http://localhost:4000'))
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Start the GraphQL server

To start the GraphQL server, run the following command:

npm run start
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Explore the GraphQL API of the application layer in a Playground

The GraphQL API of your application layer now exposes the six operations defined in schema.graphql.

To test these operations, navigate your browser to http://localhost:4000 where a GraphQL Playground is running.

Learn more about the GraphQL Playground

A GraphQL Playground is an interactive GraphQL IDE that lets you explore the operations of GraphQL API. You can click the green SCHEMA-button at the right edge of the Playground window to view the auto-generated documentation for your GraphQL API.

Here are a few sample queries and mutations you can send to explore the API.

mutation {
  createUser(name: "Jane") {
    id
  }
}
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In some snippets, you need to replace the __USER__ID__ or __POST_ID__ placeholder with the ID of an actual user or post.