Database
db={"coll1":[{_id:"5f82f1618cfa6d290c6271a9",name:"mehdi"}],"coll2":[{_id:"5f82f1618cfa6d290c6271aa",fid:"5f82f1618cfa6d290c6271a9",family:"parastar"}],}
Query
db.coll1.aggregate([{$lookup:{from:"coll2",localField:"_id",foreignField:"fid",as:"collection"}}])