Add the ability to use database-level CHECK CONSTRAINTS

[Matthew Schinckel]

I mentioned adding database level CHECK CONSTRAINTS in a post on django-developers.

​http://groups.google.com/group/django-developers/browse_thread/thread/38937992972c7808

Attached to this ticket is a patch that provides the functionality listed in the first post of this thread. This is not complete: it only allows simple constraints, and is missing a complete test suite.

[Matthew Schinckel]

Contains patches against trunk that enable check constraints

[Russell Keith-Magee]

If we do this, it should be tied into the model validation framework in some way.

[Matthew Schinckel]

Agreed. The initial patch was made before the changes with model validation had hit. I will get back to this at some stage.

[Aymeric Augustin]

Change UI/UX from NULL to False.

[Aymeric Augustin]

Change Easy pickings from NULL to False.

[Rich Rauenzahn]

Could/should this feature request also handle this case of constraint I brought up in this thread?

https://code.djangoproject.com/ticket/11964

Basically unique_together doesn't consider a null value unique per SQL spec -- which makes perfect sense in single column indexes and is extended to multi column indexes.

So if someone wanted (A, B, NULL) to be a unique row there would need to be an index built on the first two columns "where <third column> is null"

These SO articles give a better overview:

​http://stackoverflow.com/questions/17510261/django-unique-together-constraint-failure
​http://dba.stackexchange.com/questions/9759/postgresql-multi-column-unique-constraint-and-null-values

[alexpirine]

I would also love this feature.

[Tim Graham <timograham@…>]

In 19b2dfd1:

Refs #11964, #26167 -- Made Expressions deconstructible.

[Tim Graham <timograham@…>]

In 508b5deb:

Refs #11964 -- Made Q objects deconstructible.

[Luke Plant]

This external project seems to implement this feature:

​https://github.com/rapilabs/django-db-constraints

It does some monkey patching that would be unnecessary if this were in core.

[Ian Foote]

Now that Django 2 is released, I'd like to see this land. I think I've resolved all the outstanding issues raised on the pull request before. Is the next step to rebase/squash my work in progress commits?

[Asif Saifuddin Auvi]

conflicts needed to be resolved and squash for final review I believe.

[Ian Foote]

Conflicts fixed and commits squashed.

[Tim Graham]

Please don't check "Patch needs improvement" only because there's a small merge conflict (as far as I can see, there's no outstanding review comments on the patch).

[Tim Graham <timograham@…>]

In 952f05a6:

Fixed #11964 -- Added support for database check constraints.

[Gavin Wahl]

Is it now possible to define a field that comes with a check constraint, or can they only be defined at the table level? I'd like to be able to define my own StrictlyPositiveIntegerField.

[Tim Graham <timograham@…>]

In 9a0e0d96:

Refs #11964 -- Renamed a database check constraint test.