Getting number of likes for a user in all his posts using mongodb

Question

Hi I want to build a leader board that will rank users based on the likes they have accumulated in all their posts.

My database for Posts

  user: {
    type: Schema.Types.ObjectId,
  },
  text: {
    type: String,
    required: true,
  },
  imageURL: {
    type: [String],
  },
  name: {
    type: String,
    required: true,
  },
  category: {
    type: String,
  },
  likes: [
    {
      user: {
        type: Schema.Types.ObjectId,
      },
    },
  ],
  date: {
    type: Date,
    default: Date.now,
  }

My database for user:


  name: {
    type: String,
    required: true,
  },
  email: {
    type: String,
    required: true,
    unique: true,
  },
  password: {
    type: String,
    required: true,
  },
  date: {
    type: Date,
    default: Date.now,
  },

I have tried various queries and aggregation functions but I am not able to get the right solution for that. Is there another way to do get the list. I want to get a list of users and total likes they got in all their posts combined. How can I do that ?

score 2 · Accepted Answer · answered Jun 08 '20 at 16:22

You can try this query

db.collection.aggregate([
  {
    $project: {
      user: 1,
      numberOfLikes: {
        $cond: {
          if: {
            $isArray: "$likes"
          },
          then: {
            $size: "$likes"
          },
          else: "NA"
        }
      }
    }
  }
])

You can find demo of this query here

score 0 · Answer 2 · answered Jun 08 '20 at 16:25

I recently have the same scenario, here's how I solved it:

I created 3 different Models. Users, Posts, Likes. The Post model will be:

 user: {
    type: Schema.Types.ObjectId,
  },
  text: {
    type: String,
    required: true,
  },
  imageURL: {
    type: [String],
  },
  name: {
    type: String,
    required: true,
  },
  category: {
    type: String,
  },
  date: {
    type: Date,
    default: Date.now,
  }

The Likes model:

postId: {
  type: Schema.Types.ObjectId,
  required: true
},
userId: {
  type: Schema.Types.ObjectId,
  required: true
},
likedBy: {
  type: Schema.Types.ObjectId,
  ref: 'User',
  required: true,
}

While fetching the post, you can use aggregate function and fetch the likes with the post as shown here.
If you want to fetch the number of likes the user has received, You can do it easily by: Like.find({userId}).countDocuments()

Avoid using arrays in such cases. Because there can be no limit for user likes. If your Application grows, managing likes this way would be a nightmare.

I actually kinda solved it, though not proud of the solution I added 2 more fields in profile model namely numberPosts and likes. And in the route of like, dislike,create / delete post I have called the profile model and updated every time. — Sarthak Agrawal, Jun 09 '20 at 08:11
Thats cool, but don't use likes as an array in Post schema, use separate model of Like instead. :) — Syed Zubair Ahmed, Jun 09 '20 at 09:01

Getting number of likes for a user in all his posts using mongodb

2 Answers2