Question

I want to write a query that does something like this SQL query:

SELECT name FROM contacts WHERE blah blah

I know I can do something like this:

for contact in Contacts.gql(WHERE_CLAUSE, args).fetch(1000):
  print contact.name

but isn’t there a way to get name directly from a query without having to loop on the results? would it provide any advantage in performance?

Answer 1

Nope. Can’t be done.

A GQL query returns zero or more entities or Keys of the requested
kind. Every GQL query always begins with either SELECT * or SELECT
key. (A GQL query cannot perform a SQL-like “join” query.)

http://code.google.com/appengine/docs/python/datastore/gqlreference.html

But you can create a simple wrapper to do it for you. Something like:

def get_all_of_field(model, field):
  for x in model.all():
    yield getattr(x, field)

names = get_all_of_field(Contact, 'name')

Performance can’t be improved that way as the entire “line” is read by the API no matter what. Either you read the entire “line” or just its key.