Question

Here is what I do:

class Person(db.Model):  
  first_name = db.StringProperty()
  last_name = db.StringProperty()
  middle_name = db.StringProperty()
  ...
  photo = db.BlobProperty()

person = Person.get_by_key_name(person_key_name)
if person == None or not person.photo:
  self.response.set_status(404, 'Not Found')
  return      
self.response.headers['Content-Type'] = "image/png"
self.response.out.write(person.photo)

Shouldn’t I use SELECT with just one field (photo) instead of get_by_key_name?

Answer 1

No.

GQL is not SQL. There is no way of doing a SELECT query with “just one field” – you can only do either SELECT * or SELECT __key__.