How to do an aggregate query on an embedded document? - php

Question

I am using jenssegers/laravel-mongodb library in a laravel application however I need to show counts of an embedded document. Using a generic example of comment/posts, while I can solve my problem by just pulling all the posts and looping through to get comments to count them but was just was not sure if I could query them.
I did set up my relationships. In my post class I did:
public function comments()
{
return $this->hasMany('App\Comment');
}
and in my comment class:
public function post()
{
return $this->belongsTo('App\Post');
}
Later in code:
$post->comments()->save($comment);
$comment->post()->associate($post);
my document structure:
"posts" : [
{
"_id" : ObjectId("5805a11e2594ee26543ea041"),
"Post_Num" : "166236001010",
"updated_at" : ISODate("2016-10-18T04:12:14.454Z"),
"created_at" : ISODate("2016-10-18T04:12:14.451Z"),
"comments" : [
{
"Comment_Num" : "3333333",
"_id" : ObjectId("5805a11e2594ee26543ea042"),
"post_id" : "5805a11e2594ee26543ea041",
},
{
"Comment_Num" : "3333333",
"_id" : ObjectId("5805a11e2594ee26543ea042"),
"post_id" : "5805a11e2594ee26543ea041",
}
]
},
{
"_id" : ObjectId("5805a11e2594ee26543ea041"),
"Post_Num" : "166236001010",
"comments" : [
{
"Comment_Num" : "3333333",
"_id" : ObjectId("5805a11e2594ee26543ea042"),
"post_id" : "5805a11e2594ee26543ea041",
}
]
}
]
Now when I try getting the comments like:
$post->comments()->count()
or
$post->comments()->get()->count()
or
$post->comments->get()->count()
I get a 0. The same logic works if it is not an embedded document but just was wondering if it was possible to do an aggregate query ? Perhaps is best to just let the code iterate and add everything?
As you can tell I need some minor hand holding. Thank You
UPDATE: I am trying the following
public function commentCount()
{
$commentsCount = Post::raw(function($collection)
{
return $collection->aggregate(['$project' => ['_id' => 1,
'comments_count' => ['$size' => '$comments']],
['$group' => ['_id' => null, 'count' => ['$sum' => '$comments_count']]]]);
});
return $commentsCount;
}
What I get now is:
$pipeline is not a list (unexpected index: "$project")

Answer 1

Just to be clear, you want a list of your posts with the number of comments on each post?
Aggregation has something to offer for that:
https://docs.mongodb.com/manual/reference/operator/aggregation/size/#exp._S_size
I'm not a php dev but this is my shot at it:
Post::raw()->aggregate(
['$project' => ['_id' => 1,
'Post_Num' => 1,
'comments_count' => ['$size' => '$comments']],
['$group' => ['_id' => null, 'count' => ['$sum' => '$comments_count']]]
]);