handling nulls and zero values in django

If I have a model with a nullable field:

class Something(models.Model):
    parameter = models.FloatField(blank=True,null=True)

开发者_JAVA百科I then want to handle this in a view or template.

If something.parameter has a value, I want to return the value, and if it is null, I want to return 'N/A'.

If I use:

something = Something.objects.get(id=1)
output_string = 'parameter value: %s' % (something.parameter or 'N/A')

then this works, except in the case where something.parameter=0, which also returns 'N/A' rather than the desired '0'.

How can I correct this behaviour?

Is there a way of doing this directly in the template?

Use the default_if_none template filter:

{{ value|default_if_none:"N/A" }}

You could filter your data by isnull (http://docs.djangoproject.com/en/dev/ref/models/querysets/#isnull)

something = Something.objects.filter(parameter__isnull=False)

Then you can check if your query returns any results and set your parameter accordingly:

if something:
    parameter=something[0].parameter
else:
    parameter="N/A"