This one will help people use their databases more efficiently.
The Django ORM should allow users to specify a list of field names to *exclude* from a QuerySet. If a user attempts to access one of those excluded fields on the resulting model instance, the field will be loaded lazily via a separate query.
This is useful when you know you absolutely will not need to use a particular field in your template, so there's no point in SELECTing that data. This saves memory, and it saves on bandwidth between the database server and the Web server.
Example:
class Person(models.Model):
name = models.CharField(maxlength=32)
age = models.IntegerField()
hometown = models.CharField(maxlength=32)
is_cool = models.BooleanField()
# My instinct is to call this hide(), but I'm sure there's a better name for it.
>>> p = Person.objects.hide('hometown', 'is_cool').get(name='John Lennon')
>>> p.id
3
>>> p.name
u'John Lennon'
# Does a query to get "hometown", because it was hidden from the QuerySet.
# 'SELECT hometown FROM person WHERE id=3;'
>>> p.hometown
u'Liverpool'
# Does a query to get "is_cool", because it was hidden from the QuerySet.
# 'SELECT is_cool FROM person WHERE id=3;'
>>> p.is_cool
True
In the case of lazily loaded fields, the lazy loading *only* applies to the particular field. E.g., when I accessed p.hometown in the above example, it did *not* also lazily load the rest of the hidden fields ("is_cool").
We should also provide the inverse of hide() -- perhaps called expose()? -- which would take a list of field names to *include* rather than *exclude*. This would be an opt-in instead of an opt-out.
