const PostSchema = new mongoose.Schema({
  title: {
    type: String,
  },
  text: {
    type: String,
    required: true,
  }
  postedBy: {
    type: mongoose.Schema.ObjectId,
    ref: "User",
  }
  likes: [{
    type: mongoose.Schema.ObjectId,
    ref: "User",
  }, ],
  likeLength: {
    type: Number,
    default: 0
  }
});


let totalLikes = Post.aggregate([{
    $match: {
      postedBy: req.profile._id,
    },
  },
  {
    $group: {
      _id: "$postedBy",
      total_count: {
        $sum: "$likeLength"
      }
    }
  },
])

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I wanted to sum likeLength values in all Post collections filtered by postedBy field and get the summed result which type of integer. I tried totalLikes function above but could not make it.

CodePudding user response：

Maybe this can help

• make the string req.profile._id to ObjectId
• group by null all are from the same postedBy so all document that passed are in group. (group by null means all collection 1 group) (your group was ok also but this is simpler)
• unset the _id to get as result [{"total_count" : 20}] for example

*before testing the group test if $match works and documents are found.

let totalLikes = Post.aggregate([{
    $match: {
      postedBy: mongoose.Types.ObjectId(req.profile._id),
    }
  },
  {
    $group: {
      _id: null,
      total_count: {
        $sum: "$likeLength"
      }
    }
  },
  {"$unset": ["_id"]}
])

CodePudding user response：

The solution for that is the following. With result[0] the result will be an object with sumLikes property.

aggregate([
      {
        $match: {postedBy: req.profile._id}
      },
      {
        $group: {
          _id: null,
          sumLikes: {
            $sum: "$likeLength",
          },
        },
      },
      { $unset: ["_id"] },
    ], function(err, result) {
      if(err){
        console.log(err)
      }else{
        res.json(result[0])
      }})

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