MongoDB子文档或父文档引用的优势

MongoDB双向关联引用的优势在于可以同时定义文档关系，而无需提供维护文档关系所需的额外代码。在此方法中，MongoDB使用ObjectId数据类型来引用其他文档的_id字段。使用这种引用类型与embed文档相比，提供了更好的灵活性，并且可以有效地管理数据模型更改。另外，常规查询中可以查询到自己所需的相关数据，而无需进行多次查询。

示例：

// User schema const UserSchema = new mongoose.Schema({ email: String, password: String }); const User = mongoose.model('User', UserSchema);

// Post schema with parent reference to User const PostSchema = new mongoose.Schema({ title: String, content: String, author: { type: mongoose.Schema.Types.ObjectId, ref: 'User' } }); const Post = mongoose.model('Post', PostSchema);

// Comment schema with child reference to Post and parent reference to User const CommentSchema = new mongoose.Schema({ text: String, author: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }, post: { type: mongoose.Schema.Types.ObjectId, ref: 'Post' } }); const Comment = mongoose.model('Comment', CommentSchema);

// Create a new User, Post and Comment const user = await User.create({ email: 'example@email.com', password: 'password' }); const post = await Post.create({ title: 'My first post', content: 'Hello world!', author: user._id }); const comment = await Comment.create({ text: 'Nice post!', author: user._id, post: post._id });

// Find all Comments for a Post and populate the parent User const comments = await Comment.find({ post: post._id }).populate('author'); console.log(comments); // [{ text: 'Nice post!', author: { email: 'example@email.com' }, post: post._id }]