Express-graphql“在运行突变和查询时无法使用 mongodb 读取未定义的属性‘集合’”

Posted 2023-03-08

【中文标题】Express-graphql“在运行突变和查询时无法使用 mongodb 读取未定义的属性‘集合’”

【英文标题】：Express-graphql "Cannot read property 'collection' of undefined" with mongodb while runing mutation & query

【发布时间】：2020-05-05 05:25:11

【问题描述】：

我正在尝试使用 express-graphql、node 和 mongodb 查询图 QL 中的突变。对于查询和突变，我得到“无法读取未定义的属性'集合'”。我进入数据库，那里有一个包含文档的集合。稍后可以在上下文中添加身份验证。在过去的两天里，我尝试了多种命名该系列的变体，但均未成功。我需要声明一个常量吗？我错过了什么？

服务器.js

const express = require('express');
const graphqlHTTP = require('express-graphql');
const schema = require('./graphql/schema')
const mongoose1 = require('./mongoDB')
const expressPlayground = require('graphql-playground-middleware-express').default;
const cors = require('cors')

const Event = require('./models/events')

const app = express();

app.use(cors())

app.use(express.json());

// DB
const context = async () => 
    const db = await mongoose1;

    return  db ;
;


// Provide resolver functions for your schema fields
const resolvers = 
    events: async (_, context) => 
        const  db  = await context();
        return db
            .collection('events')
            .find()
            .toArray();
    ,
    event: async ( _id , context) => 
        const  db  = await context();
        return db.collection('events').findOne( _id );
    ,
    createEvent: args => 
        const event = new Event(
            title: args.eventInput.title,
            description: args.eventInput.description,
        )
        return event.save().then(res => 
            console.log(res);
            return  ...res._doc 
        ).catch(err => 
            console.log(err)
            throw err
        );
    


app.use(
    "/graphql",
    graphqlHTTP(
        schema,
        rootValue: resolvers,
        context,
    )
);
app.get('/playground', expressPlayground( endpoint: '/graphql' ))
app.listen(5000);

console.log(`???? Server ready at http://localhost:5000/graphql`); 

数据库

require('dotenv').config()
const mongoose = require('mongoose');

const db = process.env.MONGODB

const mongoose1 = mongoose
    .connect(db, 
        useNewUrlParser: true,
        useCreateIndex: true,
        useUnifiedTopology: true
    ) 
    .then(() => console.log('MongoDB Connected...'))
    .catch(err => console.log(err));


module.exports = mongoose1

架构

const  buildSchema  = require('graphql');


// Construct Schema
const schema = buildSchema(`
    type Event 
        _id: ID!
        title: String!
        description: String
        date: String

    

    input EventInput 
        title: String!
        description: String
        date: String

    

    type Query 
        events: [Event!]!
        event(_id: String!): Event!
    

    type Mutation 
        createEvent(eventInput: EventInput): Event
    
`);

module.exports = schema

型号

const mongoose = require('mongoose');

const Schema = mongoose.Schema;

const eventSchema = new Schema(
    title: 
        type: String,
        required: true
    ,
    description: 
        type: String,
        required: true
    ,
    date: 
        type: Date,
        default: Date.now
    
)

module.exports = mongoose.model('Event', eventSchema)

【参考方案1】：

mongoDB.js 导出的函数返回一个 Promise，但该 Promise 解析为 undefined，因为 console.log 返回未定义。由于connect 应该解析为调用它的Mongoose 实例的值，因此要么完全删除then 调用，要么确保在其中返回Mongoose 实例。