db={"dashboard":[{"_id":"dashboard1","name":"test","user":1}],"templatefolders":[{"dashboardId":"dashboard1","folderId":"folder123","name":"folder","region":"XXX"}],"folders":[{"_id":"folder123"}],"user":[{"_id":1,"name":"alaa"}],}

db.dashboard.aggregate([{$lookup:{from:"templatefolders",let:{"boardId":"$_id"},pipeline:[{$match:{$expr:{$eq:["$dashboardId","$$boardId"]}}},{$lookup:{from:"folders",let:{"folderId":"$folderId"},pipeline:[{$match:{$expr:{$eq:["$_id","$$folderId"]}}},],as:"joinFolder"},},],as:"joinDashboard"}}])