how to get the count of documents with value in different fields in mongo
We need create a Set of unique lender_id and borrower_id like shown below (by changing the order). In the last stage, we take the Set size.
chats = await Chat.aggregate([ { $match: { $or: [ {lender_id: 10}, {borrower_id: 10} ] } }, { $group: { _id: null, differentChats: { $addToSet: { $cond: [ { $gt: ["$lender_id", "$borrower_id"]}, [ "$lender_id", "$borrower_id" ], [ "$borrower_id", "$lender_id" ] ] } } } }, { $project: { differentChats: { $size: "$differentChats" } } }])