Database
db={"posts":[{"_id":"1234","body":" hello ! I love mongodb, but its hard","liked":true,"likesCount":1,likes:[34,35,36],comments:{"_id":"3453","body":"me I don't like mongodb i like sql ","liked":true,"likesCount":1,likes:[34,35,36],replies:{"_id":"2345","body":"both of them are great","liked":true,"likesCount":1,likes:[34,35,36],},}}]}
Query
db.posts.aggregate([{$project:{_id:1,body:1,liked:{$in:[34,"$likes"]},likesCount:{$size:"$likes"},comments:{_id:1,body:1,liked:{$in:[34,"$likes"]},likesCount:{$size:"$likes"},}}}])