GraphQL教程三：类型及关系

在前面介绍了GraphQL的设计理念及安装配置及Schema的基本使用，下面来说说GraphQL中的类型。

GraphQL教程

GraphQL系列教程：

• GraphQL的设计理念及安装配置
• Schema的基本使用
• GraphQL中的类型及类型间的关系
• 使用MongoDB作为数据存储层
• 在React中使用GraphQL
• 在AWS Appsync中使用GraphQL
• 如何在serverless中定义GraphQL API-不使用AppSync
• 如何在serverless中定义GraphQL API-使用AppSync并使用Lambda作为数据源

基本类型：GraphQLID

在GraphQL中，GraphQLID的作用是来标识一条数据的。对应的数据可以是数字或者字符串。比如StudentType的类型定义可以为：

javascript

const {GraphQLObjectType, GraphQLString, GraphQLSchema, GraphQLID} = graphql;

const StudentType = new GraphQLObjectType({
    name: 'Student',
    fields: () => ({
        id: {type: GraphQLID},
        name: {type: GraphQLString},
        address: {type: GraphQLString}
    })
});

定义Student和Tutor之间的关系

测试数据

javascript

var students = [
    { id: '1', name: 'Lucas', address: '1 Fake Street', tutorid: "1" },
    { id: '2', name: 'Paul', address: '2 Fake Street' , tutorid: "2"},
    { id: '3', name: 'Jess', address: '3 Fake Street', tutorid: "3" },
    { id: '4', name: 'Tom', address: '4 Fake Street', tutorid: "4" },
    { id: '5', name: 'Ned', address: '5 Fake Street', tutorid: "2" },
    { id: '6', name: 'Dan', address: '6 Fake Street', tutorid: "2" },
    { id: '7', name: 'Luke', address: '7 Fake Street', tutorid: "2" },
    { id: '8', name: 'Lucy', address: '8 Fake Street', tutorid: "3" },
    { id: '9', name: 'Chole', address: '9 Fake Street', tutorid: "3" },
    { id: '10', name: 'Amy', address: '10 Fake Street', tutorid: "4" },
];

var tutors = [
    {id: '1', name: 'Dr Kerridge'},
    {id: '2', name: 'Prof Kennedy'},
    {id: '3', name: 'Prof Harding'},
    {id: '4', name: 'Dr Tang'},
];

更新RootQuery

一旦添加了多个类型，就需要在RootQuery中声明多个入口：

javascript

const RootQuery = new GraphQLObjectType({
    name: 'RootQueryType',
    fields: {
        student: {
            type: StudentType,
            args: {id: {type: GraphQLID}},
            resolve(parent, args) {
                return _.find(students, { id: args.id });
            }
        },
        tutor: {
            type: TutorType,
            args: {id: {type: GraphQLID}},
            resolve(parent, args) {
                return _.find(tutors, { id: args.id });
            }
        }
    }
});

定义Student到Tutor的一对一关系

javascript

const StudentType = new GraphQLObjectType({
    name: 'Student',
    fields: () => ({
        id: {type: GraphQLID},
        name: {type: GraphQLString},
        address: {type: GraphQLString},
        tutor: {
            type: TutorType,
            resolve(parent, args) {
                return _.find(tutors, {id: parent.tutorid})
            }
        }
    })
});

定义由Tutor到Student之间的一对多关系

javascript

const TutorType = new GraphQLObjectType({
    name: 'Tutor',
    fields: () => ({
        id: {type: GraphQLID},
        name: {type: GraphQLString},
        students: {
            type: new GraphQLList(StudentType),
            resolve(parent, args) {
                return _.filter(students, {tutorid: parent.id})
            }
        }
    })
});

这样就可以进行如下查询了：

GraphQL教程

支持更多的Root Query

可以增加students这个Root Query：

javascript

students: {
    type: new GraphQLList(StudentType),
    resolve(parent, args) {
        return students;
    }
}

这样就可以进行如下的查询：

GraphQL教程

同理，可以定义tutors这个Root Query：

javascript

tutors: {
    type: new GraphQLList(TutorType),
    resolve(parent, args) {
        return tutors;
    }
}

这样就可以进行如下GraphQL查询：

json

{
  tutors {
    name
    students {
      name
    }
  }
}

至此，我们已经支持4种不同的Root Query了：

GraphQL教程