MongoDB aggregate lookup not working with multiple parameters

Question

I am pulling data from comments table and it works. I want to do a join equivalent with performance in mind on the users collection to get details about the user who commented.

Here is my code where I use Next js. I added the aggregate/ lookup and now I dont get anything back.

  const from = req.query.from ? new Date(req.query.from) : new Date();
  const postId = req.query.by;
  const comments = await req.db
    .collection('commentsPosts')
    .find({
      commentedAt: {
        $lte: from,
      },
      ...(postId && { postId }),
    })
    .sort({ commentedAt: -1 })
    .limit(parseInt(req.query.limit, 10) || 10)

    //This part is not working and breaking the whole query
    .aggregate({
      $lookup:{
          from:"users",
          localField:"createdBy",
          foreignField:"_id",
          as:"commenterDetails"
          }
      })
     /////////////
    .toArray();

  res.send({ comments });

Edit

Updated as per the answer below but still no results

   .collection('commentsPosts')
    .aggregate(
      [
       {$match:{
        commentedAt: {
          $lte: from,
        },
        ...(postId && { postId }),
        }
        .sort({ commentedAt: -1 })
        .limit(parseInt(req.query.limit, 10) || 10)
       },
       {$lookup:
          {
                from:"users",
                localField:"createdBy",
                foreignField:"_id",
                as:"commenterDetails"
          }
        }
      ]
    ).toArray();

Please take a look at the Aggregation Stages, the stages you are trying to use, and some examples. — prasad_
– prasad_, Commented Aug 6, 2020 at 7:21

Vibhav Singh Rohilla · Accepted Answer · 2020-08-06 03:23:33Z

4

you do not need to do a find() when you are planning to use aggregate()

Remove the find() and introduce a $match in aggregate pipeline.

db.comments.aggregate(
  [
   {$match:{commentedAt:{$gt:QUERY_CLAUSE_HERE}},
   {$lookup:{...}}
  ]
)

answered Aug 6, 2020 at 3:23

Vibhav Singh Rohilla

7681 gold badge5 silver badges19 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

FKM Over a year ago

Thanks but I have lots of stuff going on. I updated the question with what I tried based on your answer but still no results and no errors.

ippi Over a year ago

@FKM: But is it even possible? Mongoose has no support for aggregating from queries. MongoDB documentation has db.collection.aggregate and db.aggregate and nothing else. Besides, everything you can do with a find() you can also do with $match, and you can sort and limit with aggregate as well.

Vibhav Singh Rohilla Over a year ago

@FKM the solution which I posted is application on mongo3.6 version and later. Which version are you currently working? And please keep in mind aggregate pipeline executes in sequence. Please consider keeping sort and limit after aggregate.

FKM Over a year ago

@Vibhav Singh Rohilla - I am using mongo db compass community version 1.21.2

Collectives™ on Stack Overflow

MongoDB aggregate lookup not working with multiple parameters

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related