Mongoose find() 方法在我第一次运行节点时没有返回值

Question

这个想法很简单。我在“fruitsDB”内的“fruits”集合中添加了 4 个条目。当我运行 server.js 时，它实际上将列表条目添加到数据库中。

当我检查数据库时，它说我有 4 个条目 [苹果、猕猴桃、橙子、香蕉]。但是 find 方法是

Fruit.find(function(err, fruits){
    if(err){
        console.log(err);
    } else {
        console.log(fruits);
} });

当我第一次运行 server.js 时返回一个空数组。如果我第二次运行 server.js 并检查 MongoDB 内部的集合，因为这是第二次运行新的集合内容显示如下

[苹果、猕猴桃、橙子、香蕉、苹果、猕猴桃、橙子、香蕉]

这次 find() 方法显示了数组，但只有 4 个……我在这里做错了什么？

Server.js：

const mongoose = require('mongoose');

main().catch(err => console.log(err));

// This section means connect to mongodb and create fruitsDB database inside that
async function main() {
    await mongoose.connect('mongodb://localhost:27017/fruitsDB');
  }

const fruitSchema = new mongoose.Schema({
    name: String,
    rating: Number,
    review: String
});

const Fruit = mongoose.model('Fruit', fruitSchema);

//  MongoDB will automatically pluralize the collection name
// const fruit = new Fruit({
//     name: 'Apple',
//     rating: 7,
//     review: 'Pretty solid as fruit!'
// });

// Comment out this section to prevent mongoose to 
    // save fruit to fruits collection everytime you run server.js
// fruit.save();

const peopleSchema = new mongoose.Schema({
    name: String,
    age: Number
});

const People = mongoose.model('People', peopleSchema);

const people = new People({
    name: 'John',
    age: 37
});

people.save();

const apple = new Fruit({
    name: 'Apple',
    rating: 7,
    review: 'Pretty solid as fruit!'
});

const kiwi = new Fruit({
    name: 'Kiwi',
    rating: 10,
    review: 'The best fruit!'
});

const orange = new Fruit({
    name: 'Orange',
    rating: 4,
    review: 'Too sour for me!'
});

const banana = new Fruit({
    name: 'Banana',
    rating: 3,
    review: 'Weird texture!'
});

Fruit.insertMany([apple, kiwi, orange, banana], function(error){
    if(error){
        console.log(error);
    } else {
        console.log('New entries are added to the database!');
    }
});

// Read the fruits collection
Fruit.find(function(err, fruits){
    if(err){
        console.log(err);
    } else {
        console.log(fruits);
    }
});

Answer 1

您必须等待 Mongoose 连接到您的 MongoDB 服务器，然后您应该执行所有逻辑。您可以做的只是将所有逻辑放在main() 函数中await mongoose.connect('mongodb://localhost:27017/fruitsDB'); 之后。这将确保 Mongoose 在执行任何数据库查询之前连接到 MongoDB 服务器。

const mongoose = require('mongoose');

main().catch(err => console.log(err));

// This section means connect to mongodb and create fruitsDB database inside that
async function main() {
  await mongoose.connect('mongodb://localhost:27017/fruitsDB');

  const fruitSchema = new mongoose.Schema({
    name: String,
    rating: Number,
    review: String
  });

  const Fruit = mongoose.model('Fruit', fruitSchema);

  //  MongoDB will automatically pluralize the collection name
  // const fruit = new Fruit({
  //     name: 'Apple',
  //     rating: 7,
  //     review: 'Pretty solid as fruit!'
  // });

  // Comment out this section to prevent mongoose to 
  // save fruit to fruits collection everytime you run server.js
  // fruit.save();

  const peopleSchema = new mongoose.Schema({
    name: String,
    age: Number
  });

  const People = mongoose.model('People', peopleSchema);

  const people = new People({
    name: 'John',
    age: 37
  });

  people.save();

  const apple = new Fruit({
    name: 'Apple',
    rating: 7,
    review: 'Pretty solid as fruit!'
  });

  const kiwi = new Fruit({
    name: 'Kiwi',
    rating: 10,
    review: 'The best fruit!'
  });

  const orange = new Fruit({
    name: 'Orange',
    rating: 4,
    review: 'Too sour for me!'
  });

  const banana = new Fruit({
    name: 'Banana',
    rating: 3,
    review: 'Weird texture!'
  });

  Fruit.insertMany([apple, kiwi, orange, banana], function(error) {
    if (error) {
      console.log(error);
    } else {
      console.log('New entries are added to the database!');
    }
  });

  // Read the fruits collection
  Fruit.find(function(err, fruits) {
    if (err) {
      console.log(err);
    } else {
      console.log(fruits);
    }
  });
}

Answer 2

find() 方法在数据库有机会存储数据之前运行。
您可以使用 await 将 insertMany() 调用存储在 async 函数中，然后将 Fruit.find()之后

async function myFunc() {
    await Fruit.insertMany([apple, kiwi, orange, banana], function (error) {
        if (error) {
            console.log(error);
        } else {
            console.log('New entries are added to the database!');
        }
    });
    Fruit.find(function (err, fruits) {
        if (err) {
            console.log(err);
        } else {
            console.log(fruits);
        }
    });
}
myFunc();

---

或者利用 Promise 回调并使用 .then()。

myFunc().then(() => {
    Fruit.find(function (err, fruits) {
        if (err) {
            console.log(err);
        } else {
            console.log(fruits);
        }
    });
},err=> console.log(err));