Update and save records in a django.db.models.query.QuerySet object?

Question

In django when dealng with model objects consider the following:

>>> x = table.objects.all()
>>> x[0].coulomb1
'hello'
>>>
>>> x[0].coulomb1 = 'goodbye'
>>>
>>> x[0].coulomb1
'hello'

Please can you help me understand how to change this value and save it?

Thanks in advance :)

EDIT: I managed it with:

>>> x
[<table: table object>]
>>> y = x[0]
>>> y
<table: table object>
>>> y.coulomb1 = 'goodbye'
>>> y.coulomb1
'goodbye'
>>> y.save()
>>>
>>> x[0].coulomb1
'goodbye'

Would be nice if someone could explain why it didn't work whilst within the queryset though.

Thanks :)

Answer 1

table.objects.all() is a django.query.QuerySet object. When you run x[0], you actually calls its __getitem__ method.

You can find its implementation at github.

Below is a simplified version. I only remove the safety check and slice code.

def __getitem__(self, k):
    """
    Retrieves an item or slice from the set of results.
    """
    if self._result_cache is not None:
        return self._result_cache[k]

    qs = self._clone()
    qs.query.set_limits(k, k + 1)
    return list(qs)[0]

You see, when the queryset is not cached, each time you run queryset[index], it triggers a new sql query and returns a new object.