javascript - GraphQL:在GraphQLObjectType中用自定义类型定义GraphQLList时出错

我想学习GraphQL，并且正在编写一个代表Book-Shop的示例，其中用户可以是多本书的作者。

我的问题是我无法在UserType（GraphQLObjectType）中定义类型为“ BookType”的列表。奇怪的是，当BookType具有作者时，它不会引发任何错误。

user.js（UserType）：

const {
    GraphQLList,
    GraphQLID,
    GraphQLString,
    GraphQLObjectType,
    GraphQLNonNull,
    GraphQLInt,
     } = require('graphql');

const BookType = require('./book');
const BookSchema = require('../db/models/book');

console.log(BookType);

module.exports = new GraphQLObjectType({
    name: 'User',
    fields: () => ({
        id: { type: new GraphQLNonNull(GraphQLID) },
        name: { type: new GraphQLNonNull(GraphQLString) },
        books: {
            type: new GraphQLList(BookType),
            resolve(parent, args){
                return BookSchema.find({_id: parent.id});
            }
         }
    })
});

book.js（BookType）：

const {
    GraphQLID,
    GraphQLString,
    GraphQLObjectType,
    GraphQLNonNull,
    GraphQLInt } = require('graphql');

const UserType = require('./user');
const UserSchema = require('../db/models/user');

console.log(UserType);


module.exports = new GraphQLObjectType({
    name: 'Book',
    fields: () => ({
        id: { type: new GraphQLNonNull(GraphQLID) },
        author: {
            type: UserType,
            resolve(parent, args){
                return UserSchema.findOne({_id: parent.author});
            }
         },
        title: { type: new GraphQLNonNull(GraphQLString) },
        sites: { type: new GraphQLNonNull(GraphQLInt) }
    })
});

如您所见，我记录了BookType和UserType。奇怪的是，当我记录BookType时得到了一个空对象。

输出：

console.log(BookType) --> {}
console.log(UserType) --> User

这是错误：

Error: Expected [object Object] to be a GraphQL type.
    at invariant (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/jsutils/invariant.js:19:11)
    at assertType (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/definition.js:88:43)
    at new GraphQLList (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/definition.js:258:19)
    at fields (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/src/types/user.js:21:19)
    at resolveThunk (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/definition.js:370:40)
    at defineFieldMap (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/definition.js:532:18)
    at GraphQLObjectType.getFields (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/definition.js:506:44)
    at typeMapReducer (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:232:38)
    at /media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:239:20
    at Array.forEach (<anonymous>)
    at typeMapReducer (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:232:51)
    at /media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:239:20
    at Array.forEach (<anonymous>)
    at typeMapReducer (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:232:51)
    at Array.reduce (<anonymous>)
    at new GraphQLSchema (/media/lorenz/DATA/Privat/Programmieren/JavaScript/NodeJS/bookShop/node_modules/graphql/type/schema.js:122:28)

最佳答案

您在这里重复了很多代码。我将开始创建一个文件，将其称为schema.js。

正在开发您的RootQuery，这是一个可以帮助您的示例：

const RootQuery = new GraphQLObjectType({
  name: 'RootQueryType',
  fields: {
    user: {
      type: UserType,
      args: { id: { type: GraphQLString } },
      resolve(parentValue, args) {
        return axios
          .get(`http://localhost:3000/users/${args.id}`)
          .then(res => res.data);
      }
    },
    company: {
      type: CompanyType,
      args: { id: { type: GraphQLString } },
      resolve(parentValue, args) {
        return axios
          .get(`http://localhost:3000/companies/${args.id}`)
          .then(res => res.data);
      }
    }
  }
});

导出，然后为UserType和其他用户创建函数。这是一个例子：

const UserType = new GraphQLObjectType({
  name: 'User',
  fields: () => ({
    id: { type: GraphQLString },
    firstName: { type: GraphQLString },
    age: { type: GraphQLInt },
    company: {
      type: CompanyType,
      resolve(parentValue, args) {
        return axios
          .get(`http://localhost:3000/companies/${parentValue.companyId}`)
          .then(res => res.data);
      }
    }
  })
});

因此，您不必导出每个副本的GraphQLObjectType，而只需导出一次

module.exports = new GraphQLSchema({ query: RootQuery });

关于javascript - GraphQL:在GraphQLObjectType中用自定义类型定义GraphQLList时出错，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/49819507/