GraphQL

1. 安装

这里没使用apollo来搭建graphql，所以配置比较麻烦些。现在使用apollo来搭建graphql很主流，apollo帮助我们减少编写这些配置graphql的代码

• 不同框架安装不同的包，比如koa的话，安装koa-graphql，express安装express-graphql

2. 初识demo

import Koa from 'koa';
import Router from 'koa-router';
import graphqlHTTP from 'koa-graphql';
import { buildSchema } from 'graphql';
const app = new Koa();
const router = new Router();
// 定义类型 type Query表示查询, type Mutation表示修改
const schema = buildSchema(`
  type Query {
       hello: String             // 定义了一个查询的变量，和返回的类型
  }
`);
==========================================================
// 当用户在localhost:5000/graphql页面里输入下面这样
query {
    hello
}
// 返回值如下
{
  "data": {
    "hello": "Hello World"
  }
}
==========================================================
// rootValue类似控制器，比如这里上面schema里定义查询hello
// 那么当用户在/graphql这个页面里查询hello字段时，服务器做的相应操作
// 就在这里写
const rootValue = {
  hello: () => `Hello World`,
};
router.all(
  '/graphql',
  graphqlHTTP({
    schema,
    rootValue,
    graphiql: true,
  })
);
app.use(router.routes(), router.allowedMethods());
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => console.log(`server started at ${PORT}`));

3. 自定义类型

// 定义类型 type Query表示查询, type Mutation表示修改
const schema = buildSchema(`
  type User { 
    id: ID!                    // ! ID一定存在
    name: String
    age: Int
  }
  type Query {
    user: User
  }
`);
// rootValue类似控制器，比如这里上面schema里定义查询hello
// 那么当用户在/graphql这个页面里查询hello字段时，服务器做的相应操作
// 就在这里写
const rootValue = {
  user: () => ({
    id: nanoid(),
    name: 'Yoooo',
    age: 18,
  }),
};

4. 简单拆分文件

把schema拆分到单独的文件里

在根目录新建schema.js

index.js 需要修改下

import Koa from 'koa';
import Router from 'koa-router';
import graphqlHTTP from 'koa-graphql';
import schema from './schema';
const app = new Koa();
const router = new Router();
router.all(
  '/graphql',
  graphqlHTTP({
    schema,
    graphiql: true,
  })
);
app.use(router.routes(), router.allowedMethods());
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => console.log(`server started at ${PORT}`));

schema.js

• makeExecutableSchema作用是把类型和控制器糅合在一起，形成一个schema ```javascript import { makeExecutableSchema } from ‘graphql-tools’; import { nanoid } from ‘nanoid’;

const typeDefs = ` type User { id: ID! name: String age: Int }

type Query { user: User } `;

const resolvers = { Query: { user: () => ({ id: nanoid(), name: ‘Yoooo’, age: 12, }), }, };

// makeExecutableSchema作用是把类型和控制器糅合在一起，形成一个schema export default makeExecutableSchema({ typeDefs, resolvers, });

---
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## 5. 完全拆分
> 把type, resolver也分开
目录：<br />index.js<br />db.js<br />schema.js<br />typeDefs
- userType.graphql
resolvers
- userResolver.js
**index.js**
```javascript
import Koa from 'koa';
import Router from 'koa-router';
import graphqlHTTP from 'koa-graphql';
import schema from './schema';
const app = new Koa();
const router = new Router();
router.all(
  '/graphql',
  graphqlHTTP({
    schema,
    graphiql: true,
  })
);
app.use(router.routes(), router.allowedMethods());
const PORT = process.env.PORT || 5000;
app.listen(PORT, () => console.log(`server started at ${PORT}`));

db.js

const db = {
  users: [],
};
export default {
  getData: () => db,
  setData: (key, value) => {
    db[key] = value;
    return db;
  },
};

schema.js

import {
  makeExecutableSchema,
  mergeTypeDefs,
  loadFilesSync,
  mergeResolvers,
} from 'graphql-tools';
import { nanoid } from 'nanoid';
const typeDefs = mergeTypeDefs(loadFilesSync('./typeDefs'), { all: true });
const resolvers = mergeResolvers(loadFilesSync('./resolvers'));
// makeExecutableSchema作用是把类型和控制器糅合在一起，形成一个schema
export default makeExecutableSchema({
  typeDefs,
  resolvers,
});

typeDefs/userType.graphql

type User {
  id: ID!
  name: String
  age: Int
}
type Query {
  userList: [User]
}
type Mutation {
  createUser(name: String, age: Int): User
}

resolvers/userResolver.js

import { nanoid } from 'nanoid';
import UserModel from '../models/userModel';
export default {
  Query: {
    userList: () => UserModel.getUserList(),
  },
  Mutation: {
    createUser: (parent, args) => {
      const user = new UserModel({
        name: args.name,
        age: args.age,
      }).create();
      return user;
    },
  },
};

6. GraphQL VS Restful

• 相对于restful 很多个接口，GraphQL只有一个end point，就是/graphql
• express-graphql, apollo 这些包用来帮我们parse incoming graphql requery
• How are Schemas and Resolvers connected?
  • The express-graphql package does that