Django just keeps getting better and better.
I thought there would be hell to pay with admin form save overriding but it was surprisingly easy.
In the model you wish to enforce uniqueness, simply add a Meta class declaration and give it the property "unique_together".
unique_together = (("fieldA", "fieldB"),)
fieldA = models.ForeignKey(BlahA)
fieldB = models.ForeignKey(BlahB)
description = models.TextField()
Whalla! Now it will not let you add any rows which would break the "fieldA AND fieldB" uniqueness constraint.
The change is made at a database level so if data already exists you'll have to migrate the changes somehow.
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