Filtering for empty or NULL names in a queryset

django django-models django-queryset filter null
un33k picture un33k · May 10, 2009 · Viewed 364.1k times · Source

I have first_name, last_name & alias (optional) which I need to search for. So, I need a query to give me all the names that have an alias set.

Only if I could do:

Name.objects.filter(alias!="")

So, what is the equivalent to the above?

Answer

Sasha Chedygov picture Sasha Chedygov · May 10, 2009

You could do this:

Name.objects.exclude(alias__isnull=True)

If you need to exclude null values and empty strings, the preferred way to do so is to chain together the conditions like so:

Name.objects.exclude(alias__isnull=True).exclude(alias__exact='')

Chaining these methods together basically checks each condition independently: in the above example, we exclude rows where alias is either null or an empty string, so you get all Name objects that have a not-null, not-empty alias field. The generated SQL would look something like:

SELECT * FROM Name WHERE alias IS NOT NULL AND alias != ""

You can also pass multiple arguments to a single call to exclude, which would ensure that only objects that meet every condition get excluded:

Name.objects.exclude(some_field=True, other_field=True)

Here, rows in which some_field and other_field are true get excluded, so we get all rows where both fields are not true. The generated SQL code would look a little like this:

SELECT * FROM Name WHERE NOT (some_field = TRUE AND other_field = TRUE)

Alternatively, if your logic is more complex than that, you could use Django's Q objects:

from django.db.models import Q
Name.objects.exclude(Q(alias__isnull=True) | Q(alias__exact=''))

For more info see this page and this page in the Django docs.

As an aside: My SQL examples are just an analogy--the actual generated SQL code will probably look different. You'll get a deeper understanding of how Django queries work by actually looking at the SQL they generate.

Related questions

How do I do a not equal in Django queryset filtering?

In Django model QuerySets, I see that there is a __gt and __lt for comparative values, but is there a __ne or != (not equals)? I want to filter out using a not equals. For example, for Model: bool a; int …

Read More
How do I filter query objects by date range in Django?

I've got a field in one model like: class Sample(models.Model): date = fields.DateField(auto_now=False) Now, I need to filter the objects by a date range. How do I filter all the objects that have a date …

Read More
select and update database record with a single queryset

How do I run an update and select statements on the same queryset rather than having to do two queries: - one to select the object - and one to update the object The equivalent in SQL would be something …

Read More