Mongoose count by subobjects

Question

I am trying to count the number of models in a collection based on a property:

I have an upvote model, that has: post (objectId) and a few other properties.

First, is this good design? Posts could get many upvotes, so I didn’t want to store them in the Post model.

Regardless, I want to count the number of upvotes on posts with a specific property with the following and it’s not working. Any suggestions?

upvote.count({‘post.specialProperty’: mongoose.Types.ObjectId(“id”), function (err, count) {
    console.log(count);
});

@inspired i have a post schema that has a property of type object id. I have a up vote schema that has a property "post" that is the object id of the post. — user1947561
– user1947561, Commented Nov 5, 2015 at 17:53

Abdullah Rasheed · Accepted Answer · 2015-11-05 19:12:16Z

3

Post Schema Design

In regards to design. I would design the posts collection for documents to be structured as such:

{
    "_id" : ObjectId(),
    "proprerty1" : "some value",
    "property2" : "some value",
    "voteCount" : 1,
    "votes": [
        {
            "voter": ObjectId()// voter Id,
            other properties...
        }
    ]
}

You will have an array that will hold objects that can contain info such as voter id and other properties.

Updating

When a posts is updated you could simply increment or decrement the voteCountaccordingly. You can increment by 1 like this:

db.posts.update(
        {"_id" : postId},
        {
            $inc: { voteCount: 1},
            $push : {
                "votes" : {"voter":ObjectId, "otherproperty": "some value"}
            }
        }
)

The $inc modifier can be used to change the value for an existing key or to create a new key if it does not already exist. Its very useful for updating votes.

Totaling votes of particular Post Criteria

If you want to total the amount for posts fitting a certain criteria, you must use the Aggregation Framework.

You can get the total like this:

db.posts.aggregate(
        [
            {
                $match : {property1: "some value"}
            },
            {
                $group : {
                    _id : null,
                    totalNumberOfVotes : {$sum : "$voteCount" }
                }
            }
        ]
)

answered Nov 5, 2015 at 19:12

Abdullah Rasheed

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2 Comments

user1947561 Over a year ago

Thanks! For the up vote storing in a post -- should I still keep the up vote model, and store an array of up votes in the post?

Abdullah Rasheed Over a year ago

@user1947561 Can you put your vote model in your question and format it like the model I showed you so I can understand your model better?

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