[Pulp-dev] blank=True vs null=True for string fields

Calvin Spealman cspealma at redhat.com
Wed Jan 27 14:37:25 UTC 2021

I would say it is more than not being "the Django convention" and is in
fact a pretty risky schema in general. I think its important to
contextualize your question not as a framework one, but a more general
database best practices one.

On Wed, Jan 27, 2021 at 7:00 AM Quirin Pamp <pamp at atix.de> wrote:

> While working on this PR (
> https://github.com/pulp/pulp-2to3-migration/pull/295), there was a
> problem with duplicate units since I added a new "null=True" string field
> to a unique_together condition.
> It appeared some units ended up having a Null value, while others had the
> empty string (which was not my intention with respect to the uniqueness
> condition).
> I ended up fixing the issue by using "blank=True" instead of "null=True".
> I also found the following in the django docs:
> Avoid using null on string-based fields such as CharField and TextField
> because empty string values will always be stored as empty strings, not as
> NULL. If a string-based field has null=True, that means it has two possible
> values for “no data”: NULL, and the empty string. In most cases, it’s
> redundant to have two possible values for “no data;” the Django convention
> is to use the empty string, not NULL.
> See: https://docs.djangoproject.com/en/3.1/ref/models/fields/
> I am pretty sure I have used "null=True" for string fields within pulp_deb
> and have also seen examples of it in pulpcore. My question for the
> community is: Should we be concerned about this, given it is apparently not
> "the Django convention". Is there any chance this could be problematic,
> even if the field in question is not part of a unique_together condition?
> Are there situations where we explicitly rely on a distinction between NULL
> and empty string (making "going against the Django convention" a conscious
> choice, rather than an historical accident)?
> Looking forward to your insights,
> Quirin Pamp (quba42)
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