Question

我有两个合集：作者和书籍

作者示例：

{
   _id: "605f6746c114544ee04228bd"
   firstName: "firstName",
   lastName: "lastName",
}

书籍示例：

{
   _id: "605f6746c114544ee04228bd"
   title: "title",
   pages: 350,
}

我想获得带有作者名字和姓氏的书籍列表。

这是我当前的代码：

let books;

books = await Book.find();
books.forEach(async (book, i) => {
  const author = await Author.findOne(
    { _id: book.authorId },
    { firstName: 1, lastName: 1, _id: 0 }
  );
  books[i].authorFirstName = author.firstName;
  books[i].authorLastName = author.lastName;
});

这不是一个好习惯，因为对于每本书，我都会对 mongodb 数据库执行另一个请求！有更好的解决方案吗？

Answer 1

<块引用>

猫鼬版本加入两个有关系的模型

books = await Book.find({}).populate({ path:"authorId", select:{firstName:1, lastName:1}})

<块引用>

使用聚合

let books = await Book.aggregation([
   { 
     $lookup:{
        from:"collection_of_author",
        localField: "authorId",
        foreignField: "_id",
        as: "author"
     }
   },
  {
    $unwind: {
       path:"authorId",
       preserveNullAndEmptyArrays:true 
    }
  }])

Answer 2

使用 mongoose populate 清洁代码并提高性能

  import Book from "../models/Book";
  import Author from "../models/Author";

  let books = await Book.find().populate({
    path: "authorId",
    model: Author,
    select: { firstName: 1, lastName: 1, _id: 0 },
  });

mongodb 聚合两个集合并添加新字段

2 个答案: