Mongoose Aggregation match an array of objectIds

Question

I have a schema that Looks like this

var Post = new mongoose.Schema({
    author: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'User'
    },
    created: {
        type: Date,
        Default: Date.now
    })

I have a User Table as well. I Have a array of user ids and i am trying to search the post table based on an array of user ids

For Example

var userIds = ["575e96652473d2ab0ac51c1e","575e96652473d2ab0ac51c1d"] .... and so on 

I want to return all posts created by these users. And posts should be sorted by their creation date. Is there a way to group this post based on the user ids provided, basically match the posts for an individual user?

The result I am trying to attain is something like this:

 [{
    userAId : "56656.....",
    post : [postA, postB],
   },{ 
    userBId :"12345...", 
    post : [postA, postB]
}]

How do I write this query?

This is what I have so far

Post.aggregate([{
  // {"$unwind" : ""},
    // "$group": {
    //     _id: "$author",
    //     "created" : {"$sum" : 1 }
    // }
    "$match" : { author : id}
}]).exec(function(error, data) {
  if(error){
    return console.log(error);
  }else{
    return console.log(data)
  }
})



{
    "_id" : ObjectId("575e95bc2473d2ab0ac51c1b"),
    "lastMod" : ISODate("2016-06-13T11:15:08.950Z"),
    "author" : ObjectId("575dac62ec13010678fe41cd"),
    "created" : ISODate("2016-06-13T11:15:08.947Z"),
    "type" : "photo",
    "end" : null,
    "commentCount" : 0,
    "viewCount" : 0,
    "likes" : 0,
    "tags" : [],
    "title" : "Today is a good day",
    "__v" : 0
}

Answer 1

To return all posts created by users depicted in a list of ids, use the $in operator in your query and then chain the sort() method to the query to order the results by the created date field:

Post.find({ "author": { "$in": userIds } })
    .sort("-created") // or .sort({ field: 'asc', created: -1 });
    .exec(function (err, data){
        if(err){
            return console.log(err);
        } else {
            return console.log(data);
        }
    });

---

To get a result where you have the post id's grouped per user, you need to run the following aggregation operation:

Post.aggregate([
    { "$match" : { "author": { "$in": userIds } } },
    { "$sort": { "created": -1 } },
    {
        "$group" : {
            "_id" : "$author",
            "posts" : { "$push": "$_id" }
        }
    },
    {
        "$project": {
            "_id": 0,
            "userId": "$_id",
            "posts": 1
        }
    }
]).exec(function (err, result){
    if(err){
        return console.log(err);
    } else {
        return console.log(result);
    }
});

---

Or with the fluent API:

 Post.aggregate()
    .match({ "author": { "$in": userIds } })
    .sort("-created")
    .group({
        "_id" : "$author",
        "posts" : { "$push": "$_id" }
     })
    .project({
        "_id" : 0,
        "userId" : "$_id",
        "posts": 1
     })
    .exec(function (err, result){
        if(err){
            return console.log(err);
        } else {
            return console.log(result);
        }
    });