mongoose 填充一对多属性

Question

I'm trying populate function in mongoose docs i've searched a lot for this, i couldn't find anything. and i have one more question. is this good approach to do this since i would need books whenever i need author in my front end code is there any other ideas to get this behavior?

I've a simple example.
here is my models

const mongoose = require("mongoose");
const Schema = mongoose.Schema;

const Author = new Schema({
  name: {
    type: String,
    required: true,
  },
  books: [{ type: Schema.Types.ObjectId, ref: "Book" }],
});
const Book = new Schema({
  title: {
    type: String,
    required: true,
  },
  author: { type: Schema.Types.ObjectId, ref: "Author" },
});

module.exports = {
  Author: mongoose.model("author", Author),
  Book: mongoose.model("book", Book),
};

then I created some routes

const express = require("express");
const { Book, Author } = require("../models");
const router = express.Router();

router.get("/books", async (req, res) => {
  let books = await Book.find();
  res.send(books);
});

router.get("/authors", async (req, res) => {
  let authors = await Author.find();
  res.send(authors);
});

router.post("/book/:author", async (req, res) => {
  let { title } = req.body;
  let { author } = req.params;
  let book = new Book({
    title,
    author,
  });
  book.save().then((data) => {
    res.send(data);
  });
});

router.post("/author", (req, res) => {
  let { name } = req.body;
  let author = new Author({
    name,
  });
  author.save().then((data) => {
    res.send(data);
  });
});

module.exports = router;

then I created a new Author and new Book calling these 2 end points I created using postman

here is result from GET /authors

[
    {
        "books": [],
        "_id": "6085a6fb098c0003944b1dcd",
        "name": "john",
        "__v": 0
    }
]

why books are empty array?

I was expecting it to be something like this

[
    {
        "books": [
            {
                "_id": "6085a702098c0003944b1dce",
                "title": "hello",
            }
        ],
        "_id": "6085a6fb098c0003944b1dcd",
        "name": "joe",
        "__v": 0
    }
]

Answer 1

if your other routes have no problems when saving and retrieving data (check the result using mongo shell or Mongo compass or anything else, or better, write tests to automate things for you before coding, anyhow), you should populate books field

router.get("/authors", async (req, res) => {
  let authors = await Author.find().populate('books').lean();
  res.send(authors);
});

this is your code with out considering your http handler try it with and without populate to understand the difference

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost:27017/testX', { useNewUrlParser: true, useUnifiedTopology: true });


const Author = mongoose.model('Author', {
  name: {
    type: String,
    required: true,
  },
  books: [{ type: mongoose.ObjectId, ref: 'Book' }],
});

const Book = mongoose.model('Book', {
  title: {
    type: String,
    required: true,
  },
  author: { type: mongoose.ObjectId, ref: 'Author' },
});

(async () => {
  try {
    const book1 = new Book({ title: 'titleHere' });
    await book1.save();

    const author1 = new Author({ name: 'nameHere' });
    author1.books.push(book1);

    await author1.save();

    const authors = await Author.find().populate('books').lean();
    console.log(authors);
  } catch (error) {
    console.error(error);
  }
})();