mutation.diff

import { makeExecutableSchema } from 'graphql-tools'
 
 const typeDefs = `
   type Post {
     id: Int!
     title: String
     body: String
     author: User
   }
 
   type User {
     id: Int!
     username: String
     email: String
     posts: [Post]
   }
 
   type Query {
     posts: [Post]
     post (id: Int!): Post
     users: [User]
     user: User
   }
 
+  type Mutation {
+    addPost(title: String!, body: String!, userId: Int!): Post!
+  }
+
   schema {
     query: Query
+    mutation: Mutation
   }
 `
 
 const endpoint = 'https://jsonplaceholder.typicode.com'
 const toJSON = res => res.json()
 
 const post = (root, { id }) => fetch(`${endpoint}/posts/${id}`).then(toJSON)
 const posts = () => fetch(`${endpoint}/posts`).then(toJSON)
 
 const user = (root, { id }) => fetch(`${endpoint}/users/${id}`).then(toJSON)
 const users = () => fetch(`${endpoint}/users`).then(toJSON)
 
 const author = ({ userId }) => fetch(`${endpoint}/users/${userId}`).then(toJSON)
 const userPosts = ({ id }) => fetch(`${endpoint}/users/${id}/posts`).then(toJSON)
 
+const addPost = (root, post) => fetch(`${endpoint}/posts`, { method: 'POST', body: post })
+  .then(toJSON).then(({ id }) => ({ id, ...post }))
+
 const resolvers = {
   Query: {
     post,
     posts,
     user,
     users,
   },
+  Mutation: {
+    addPost,
+  },
   Post: {
     author,
   },
   User: {
     posts: userPosts,
   }
 }
 
 export const schema = makeExecutableSchema({ typeDefs, resolvers })