Query when parameter is none django

A better approach on the otherwise very readable @rolling-stone answer:

models = Model.objects.all()

variables = {'x':x,'y':y,'z':z}

for key, value in variables.items():
    if value is not None:
        models = models.filter(**{key: value})

Anyway, depending on the specific filter, you'll need to apply filters together in the same .filter() call, so the "blind" way only works in the simple cases. See https://docs.djangoproject.com/en/dev/topics/db/queries/#spanning-multi-valued-relationships for more information on those cases.

I do not know, if I get your question, but

Model.objects.filter(x=x, y__isnull = False, z=z)

gives you the queryset, where the ycolumn is non-null (IS NOT NULL).

Here's the relevant documentation.

EDIT: Check if y is None and build your queryset dynamically:

if y is None:
    qs = Model.objects.filter(x=x).filter(z=z)
elif z is None:
    qs = Model.objects.filter(x=x).filter(y=y)
...

If there are too many arguments to deal with, you could use something like this; assuming that x, y, z are stored in a dictionary your values:

your_values = { 'x' : 'x value', 'y' : 'y value', 'z' : 'value'}
arguments = {}
for k, v in your_values.items():
    if v:
        arguments[k] = v

Model.objects.filter(**arguments)

Something like this could work:

models = Model.objects.all()

variables = {'x':'x','y':'y','z':'z'}

for key, value in variables.items():
    if key=='x' and value:
        models = models.filter(x=value)
    if key=='y' and value:
        models = models.filter(y=value)
    if key=='z' and value:
        models = models.filter(z=value)

Because QuerySets are lazy, this doesn't involve any database activity.