Mongoengine… How can I compare two fields?

Question

For example..

class Example(Document):
    up = IntField()
    down = IntField()

and.. I want to retrieve documents whose up field is greater or equal to down. But.. this is issue.

My wrong query code would be..

Example.objects(up__gte=down)

How can I use a field that resides in mongodb not python code as a queryset value?

Answer 1

Simple answer: not possible. Something like WHERE A = B in SQL is not doable in an efficient way in MongoDB (apart from using the $where clause which should be avoided).

Answer 2

this may be what you wanted::

db.myCollection.find( { $where: "this.credits == this.debits" } );

have a look at: http://docs.mongodb.org/manual/reference/operator/query/where/

but I donot know how to use it in mongoengine.