前置资源

【官网】：https://www.apollographql.com/
【github】：https://github.com/apollographql

入门示例

安装命令： npm install apollo-server graphql

const { ApolloServer, gql } = require('apollo-server');
// 1. 定义 schema
const typeDefs = gql`
  type Book {
    title: String
    author: String
  }
  type Query {
    books: [Book]
  }
`;
// 数据准备
const books = [
  {
    title: 'The Awakening',
    author: 'Kate Chopin',
  },
  {
    title: 'City of Glass',
    author: 'Paul Auster',
  },
];
// 2. 定义 resolver
const resolvers = {
  Query: {
    books: () => books,
  },
};
// 3. 创建 server
const server = new ApolloServer({ typeDefs, resolvers });
// 4. 启动web服务
server.listen().then(({ url }) => {
  console.log(`🚀  Server ready at ${url}`);
});

整合express

安装命令： npm install apollo-server-express

此时你将不需要apollo-server，将其卸载 npm un apollo-server

const express = require('express');
const {  ApolloServer, gql  } = require('apollo-server-express');
// 1. 定义 schema
const typeDefs = gql`
  type Book {
    title: String
    author: String
  }
  type Query {
    books: [Book]
  }
`;
// 数据准备
const books = [
  {
    title: 'The Awakening',
    author: 'Kate Chopin',
  },
  {
    title: 'City of Glass',
    author: 'Paul Auster',
  },
];
// 2. 定义 resolver
const resolvers = {
  Query: {
    books: () => books,
  },
};
async function startApolloServer() {
    const app = express();
    const server = new ApolloServer({
        typeDefs,
        resolvers,
    });
    await server.start();
        // 将ApolloServer和express进行整合
    server.applyMiddleware({ app });
    app.use((req, res) => {
        res.status(200);
        res.send('Hello!');
        res.end();
    });
    await new Promise(resolve => app.listen({ port: 4000 }, resolve));
    console.log(`🚀 Server ready at http://localhost:4000${server.graphqlPath}`);
    return { server, app };
}
startApolloServer()

ApolloServer resolvers参数

解析器resolver可以选择接受四个位置参数：(parent, args, context, info)

args参数

args 参数是一个对象，其中包含 GraphQL 客户端操作提供的所有 GraphQL 参数。

// 1. 定义 schema
const typeDefs = gql`
  type User {
    id: ID!
    name: String
  }
  type Query {
    user(id: ID!): User
  }
`;
const users = [
  {
    id: '1',
    name: 'Elizabeth Bennet'
  },
  {
    id: '2',
    name: 'Fitzwilliam Darcy'
  }
];
// 2. 定义 resolver
const resolvers = {
  Query: {
    user(parent, args, context, info) {
      return users.find(user => user.id === args.id);
    }
  },
};

parent参数

parent为此字段父项的解析器的返回值（即解析器链中的前一个解析器）。对于没有父级的顶级字段的解析器（例如 Query 的字段），该值是从传递给 Apollo Server 的构造函数的 rootValue 函数中获取的。

// 1. 定义 schema
const typeDefs = gql`
# A library has a branch and books
  type Library {
    branch: String!
    books: [Book!]
  }
  # A book has a title and author
  type Book {
    title: String!
    author: Author!
  }
  # An author has a name
  type Author {
    name: String!
  }
  # Queries can fetch a list of libraries
  type Query {
    libraries: [Library]
  }
`;
//数据准备
const libraries = [
  {
    branch: 'downtown'
  },
  {
    branch: 'riverside'
  },
];
const books = [
  {
    title: 'The Awakening',
    author: 'Kate Chopin',
    branch: 'riverside'
  },
  {
    title: 'City of Glass',
    author: 'Paul Auster',
    branch: 'downtown'
  },
];
// 2. 定义 resolver
const resolvers = {
  Query: {
    libraries() {
      return libraries;
    }
  },
  Library: {
    books(parent) {
      return books.filter(book => book.branch === parent.branch);
    }
  },
  Book: {
    author(parent) {
      return {
        name: parent.author
      };
    }
  }
};

针对该架构的有效查询如下：

query GetBooksByLibrary {
  libraries {
    books {
      author {
        name
      }
    }
  }
}

此查询的结果解析器链与查询本身的层次结构相匹配：

这些解析器按上面显示的顺序执行，通过父参数将它们的返回值传递给链中的下一个解析器。解析器链如下所示（每个子链并行执行）：