Database
[{_id:ObjectId("6350e2c1a15e0e656f4a7472"),category:"business",votes:[{voteType:"like",userId:ObjectId("62314007da34df3f32f7cfc0")},{voteType:"like",userId:ObjectId("6356b5cbe2272ebf628451b1")},]},{_id:ObjectId("6350e2c1a15e0e656f4a7473"),category:"business"}]
Query
db.collection.aggregate([{"$set":{"count":{"$cond":{"if":{"$isArray":"$votes"},"then":{"$size":{"$filter":{"input":"$votes","cond":{"$eq":["$$this.voteType","like"]}}}},"else":0}}}}])