How to query mongodb with DBRef
You can use the .$id reference but it will ignore any indexes on those fields. I would suggest ignoring that method unless you are querying it directly via the terminal or want to look up something quickly. In using large collections you will want to index the field and query it using the below method.
If you want to use an index query using the following:
db.post.find('author' : { "$ref" : 'user', "$id" : 'foo' , "$db" :'database_name' })If foo is an object id
db.post.find('author' : { "$ref" : 'user', "$id" : ObjectId('foo') , "$db" :'database_name' })You can create an index on author by
db.post.ensureIndex( {'author' : 1 } );