mongodb - Can't find documents by criteria containing string objectId value -

i have collection list such:

{username: 'somename', friendid: '57d725d6b8b144044602bf74' <-- reference objectid doc } 

when query docs in collection criteria {friendid : '57d725d6b8b144044602bf74'} no results . other field query works fine.

i tried convert value objectid('57d725d6b8b144044602bf74') though value string, still no go.

why failing search type of string ?

you trying achieve 'self-join' in mongodb , seems rely on _id field generated mongodb.

i suggest supply custom _id fields document.

eg:

{_id:"alex", name:"alex", friendid:""} {_id"john", name"john", friendid:"alex"} 

and can execute queries ease on friendid field. give shot , see if make sense requirement.