How to construct a MongoDB $in query with duplicate values in Meteor

Question

I have a list of songs that I want to display to a user. Each song has a enqueue id. My problem is that several of these songs need to be displayed multiple times. I am currently using $in operator to query MongoDB which only returns three objects as there is only three unique song ids. This means that when I use spacebars in my template to iterate over the objects I am not able to get the same song to display multiple times. Any help on a solution would be much appreciated.

Current Display Order:

1. My Everything
2. This an That
3. Going off Again

The Order I Want it to Display

1. My Everything
2. My Everything
3. This an That
4. Going off Again

My code is below

Template.songList.helpers({
songs: function () {

  var idsOfSongs = ["cEbeGLR5ujCEFPtnH", "cEbeGLR5ujCEFPtnH", "qcRfAPeYMQycwodLA", "7oK4TKZiEfvZoC5Jz"]    
  return Songs.find({"_id":{$in: idsOfSongs}}).fetch();

  } 
});

Objects returned from Songs.find

[Object, Object, Object]
0: Object
_id: "cEbeGLR5ujCEFPtnH"
album: "My Everything"
artist: "Ariana Grande"

1: Object
_id: "qcRfAPeYMQycwodLA"
album: "This an That"
artist: "Mark Miller"

2: Object
_id: "7oK4TKZiEfvZoC5Jz"
album: "Going off Again"
artist: "Pick up Sticks"

Answer 1

@Blake Seven is right that mongo won't do this natively. (However a SQL database could do this via an outer join/cross-product).

Here's one possibility:

Template.songList.helpers({
  songs: function () {
    var idsOfSongs = ["cEbeGLR5ujCEFPtnH", "cEbeGLR5ujCEFPtnH", "qcRfAPeYMQycwodLA", "7oK4TKZiEfvZoC5Jz"];  
    var songsXcount = [];
    idsOfSongs.forEach(function(id){
      songsXcount.push(Songs.findOne({_id: id})); 
    }
    return songsXcount;
  } 
});

Answer 2

You can {{#each}} over the array of _ids, then inside the {{#each}}, use a {{#with}} to select the actual document.

{{#each songIds}}
    {{#with song}}
        <li><em>{{album}}</em> by {{artist}}</li>
    {{/with}}
{{/each}}

Template.songList.helpers({
    songIds: function () {
        return ["cEbeGLR5ujCEFPtnH", ...]
    },
    song: function () {
        return Songs.findOne({_id: this});
    }
});