returning json object with subset of keys

Hi

I'm using the json functionalities of postgresql 9.3.
I have a query calling json_populate_recordset like this:
json_populate_recordset(null::product, event->'products')
but it returns an error:
ERROR: cannot call json_populate_recordset on a nested object

There is indeed one key in event->'products' giving access to an array of
objects.

Is there a way to specify which keys to keep from the object? I haven't
found ti in the docs.

Here is pseudo code of what I'd like to do:
json_populate_recordset(null::product, event->'products' WITH ONLY KEYS
{'f1','f2'})

Thx

--
Web database: http://www.myowndb.com
Free Software Developers Meeting: http://www.fosdem.org event->'products'