mongoose-population

population-try

var mongoose = require('mongoose');
var Schema   = mongoose.Schema;
var ObjectId = mongoose.Types.ObjectId;

console.log('Running mongoose version %s', mongoose.version);

var UserSchema = new Schema({
    name  : String,
    posts : [{
        type : Schema.Types.ObjectId,
        ref  : 'Post'
    }]
});
var User = mongoose.model('User', UserSchema);

var PostSchema = new Schema({
    poster: {
        type : Schema.Types.ObjectId,
        ref  : 'User'
    },
    comments: [{
        type : Schema.Types.ObjectId,
        ref  : 'Comment'
    }],
    title: String
});
var Post = mongoose.model('Post', PostSchema);

var CommentSchema = new Schema({
    post: {
        type : Schema.Types.ObjectId,
        ref  : "Post"
    },
    commenter: {
        type : Schema.Types.ObjectId,
        ref  : 'User'
    },
    content: String
});
var Comment = mongoose.model('Comment', CommentSchema);



mongoose.connect('mongodb://localhost/population-test', function (err) {
    // if we failed to connect, abort
    if (err) throw err;

    // we connected ok
    createData();
});


function createData() {

    var userIds    = [new ObjectId, new ObjectId, new ObjectId];
    var postIds    = [new ObjectId, new ObjectId, new ObjectId];
    var commentIds = [new ObjectId, new ObjectId, new ObjectId];

    var users    = [];
    var posts    = [];
    var comments = [];

    users.push({
        _id   : userIds[0],
        name  : 'aikin',
        posts : [postIds[0]]
    });
    users.push({
        _id   : userIds[1],
        name  : 'luna',
        posts : [postIds[1]]
    });
    users.push({
        _id   : userIds[2],
        name  : 'luajin',
        posts : [postIds[2]]
    });

    posts.push({
        _id      : postIds[0],
        title    : 'post-by-aikin',
        poster   : userIds[0],
        comments : [commentIds[0]]
    });
    posts.push({
        _id      : postIds[1],
        title    : 'post-by-luna',
        poster   : userIds[1],
        comments : [commentIds[1]]
    });
    posts.push({
        _id      : postIds[2],
        title    : 'post-by-luajin',
        poster   : userIds[2],
        comments : [commentIds[2]]
    });


    comments.push({
        _id       : commentIds[0],
        content   : 'comment-by-luna',
        commenter : userIds[1],
        post      : postIds[0]
    });
    comments.push({
        _id       : commentIds[1],
        content   : 'comment-by-luajin',
        commenter : userIds[2],
        post      : postIds[1]
    });
    comments.push({
        _id       : commentIds[2],
        content   : 'comment-by-aikin',
        commenter : userIds[1],
        post      : postIds[2]
    });


    User.create(users, function(err, docs) {
        Post.create(posts, function(err, docs) {
            Comment.create(comments, function(err, docs) {
                // run example on here 
            });
        });
    });



}



// Query#populate examples
function example1(done) {

    User.find()
        .populate('posts', 'title', null, {sort: { title: -1 }})
        .exec(function(err, docs) {
            console.log(docs[0].posts[0].title);    // post-by-aikin
        });


    User.findOne({name: 'luajin'})
        .populate({path: 'posts', select: { title: 1 }, options: {sort: { title: -1 }}})
        .exec(function(err, doc) {
            console.log(doc.posts[0].title);        // post-by-luajin
        });

}

function example2(done) {

    Post.findOne({title: 'post-by-aikin'})
        .populate('poster comments', '-_id')
        .exec(function(err, doc) {
            console.log(doc.poster.name);           // aikin
            console.log(doc.poster._id);            // undefined

            console.log(doc.comments[0].content);  // comment-by-luna
            console.log(doc.comments[0]._id);      // undefined
        });

    Post.findOne({title: 'post-by-aikin'})
        .populate({path: 'poster comments', select: '-_id'})
        .exec(function(err, doc) {
            console.log(doc.poster.name);           // aikin
            console.log(doc.poster._id);            // undefined

            console.log(doc.comments[0].content);  // comment-by-luna
            console.log(doc.comments[0]._id);      // undefined
        });

    Post.findOne({title: 'post-by-aikin'})
        .populate(['poster', 'comments'])
        .exec(function(err, doc) {
            console.log(doc.poster.name);          // aikin
            console.log(doc.comments[0].content);  // comment-by-luna
        });

    Post.findOne({title: 'post-by-aikin'})
        .populate([
            {path:'poster',   select: '-_id'},
            {path:'comments', select: '-content'}
        ])
        .exec(function(err, doc) {
            console.log(doc.poster.name);          // aikin
            console.log(doc.poster._id);           // undefined

            console.log(doc.comments[0]._id);      // 会打印出对应的 comment id
            console.log(doc.comments[0].content);  // undefined
        });
}


// Model#populate example
function example3(done) {

    Post.find({title: 'post-by-aikin'})
        .populate('poster comments')
        .exec(function(err, docs) {

            var opts = [{
                path   : 'comments.commenter',
                select : 'name',
                model  : 'User'
            }];

            Post.populate(docs, opts, function(err, populatedDocs) {

                console.log(populatedDocs[0].poster.name);                  // aikin
                console.log(populatedDocs[0].comments[0].commenter.name);  // luna

                done();
            });
        });

}


// Document#populate example
function example4(done) {

    User.findOne({name: 'aikin'})
        .exec(function(err, doc) {

            var opts = [{
                path   : 'posts',
                select : 'title'
            }];

            doc.populate(opts, function(err, populatedDoc) {
                console.log(populatedDoc.posts[0].title);  // post-by-aikin
                done();
            });
        });
}

function done(){
    mongoose.connection.db.dropDatabase(function() {
        mongoose.connection.close();
    });
}

非常感谢博主提供的实例代码。
发现一个问题，模拟填充数据时，用户名与ID不匹配。

    comments.push({
        _id       : commentIds[2],
        content   : 'comment-by-aikin',
//aikin的userIds是0
        commenter : userIds[1],
        post      : postIds[2]
    });