How do i add/update ObjectId array in a collection using MongoDB(Mongoose)?

Question

This is What I want as a final result. I have no idea how to update array of indexes.

my Schema is built using mongoose

var postSchema  = new Schema({
    title: {type:String},
    content: {type:String},
    user:{type:Schema.ObjectId},
    commentId:[{type:Schema.ObjectId, ref:'Comment'}],
    created:{type:Date, default:Date.now}
});


var commentSchema  = new Schema({
    content: {type:String},
    user: {type:Schema.ObjectId},
    post: {type:Schema.ObjectId, ref:'Post'}
    created:{type:Date, default:Date.now}
});

My controllers are:

// api/posts/
exports.postPosts = function(req,res){
    var post = new Post({
        title: req.body.title,
        content: req.body.content,
        user: req.user._id
    });
    post.save(function(err){
        if(err){res.send(err);}
        res.json({status:'done'});
    });
};


// api/posts/:postId/comments
exports.postComment = function(req,res){
    var comment = new Comment({
        content: req.body.content,
        post: req.params.postId,
        user: req.user._id
    });
    comment.save(function(err){
        if(err){res.send(err);}
        res.json({status:'done'});
    });
};

Do I need to use a middleware? or do i need to do something in controller?

Solution

What you want is called "population" in Mongoose (see documentation), which basically works by storing references to other models using their ObjectId.

When you have a Post instance and a Comment instance, you can "connect" them like so:

var post    = new Post(...);
var comment = new Comment(...);

// Add comment to the list of comments belonging to the post.
post.commentIds.push(comment); // I would rename this to `comments`
post.save(...);

// Reference the post in the comment.
comment.post = post;
comment.save(...);

Your controller would look something like this:

exports.postComment = function(req,res) {
  // XXX: this all assumes that `postId` is a valid id.
  var comment = new Comment({
    content : req.body.content,
    post    : req.params.postId,
    user    : req.user._id
  });
  comment.save(function(err, comment) {
    if (err) return res.send(err);
    Post.findById(req.params.postId, function(err, post) {
      if (err) return res.send(err);
      post.commentIds.push(comment);
      post.save(function(err) {
        if (err) return res.send(err);
        res.json({ status : 'done' });
      });
    });
  });
};

Comments

[chridam]

On the line post.commentIds.push(comment); shouldn't it be post.commentIds.push(comment._id);?

[robertklep]

@chridam that's not necessary, Mongoose is smart :-)

[J.Correa]

the problem with this is if postId doesn't exists will trigger error but the comment will be saved anyway

[robertklep]

@J.Correa true, if the post doesn't exist you'd have to clean up the just-saved comment, or work the other way around: first find the post, and if it exists, save and add the comment.

[J.Correa]

yes, and you can use chain promises for that work, it's something that i'am just doing right now :o

[robertklep]

@J.Correa I don't think Mongoose supported promises back in 2015 ;D