mongodb - Is there a where like relation function when using pymongo? -

i have following data:

a collection named categories contains documents so:

{     "cat":"films anglais",     "path":"w:\\videos" } 

categories unique (because use upsert) or let's admit anyway.

a collection named rules contains documents so:

{     "title":"braveheart",     "regex":"^.*braveheart.*$",     "cat":"films anglais" } 

i iterating on rules. can access cat rules rule['cat']. need path categories.

i know can do:

dest = "" category in categories.find():     if category['cat'] == rule['cat']:         dest = category['path']         break 

1) prefer process database side. categories.find_one().distinct('path').where(cat=rule['cat'])? invalide know.

2) there way define sort of relation not need duplicate cat field?

lastly, have read difference between relationnal , non relationnal systems in case choice sealed.

for 1), don't want use server-side javascript here, or ever, really. it's slow , blocks lots of other operations. don't use server-side javascript try , fake joins in mongodb.

for 2), duplicating path info rules documents seems best solution. how path change? cost embedding path duplication , need more expensive set of updates if path changes, compared current setup. seems worth me, in absence of further information use case.