Unique fields that allow nulls in Django

Question

I have model Foo which has field bar. The bar field should be unique, but allow nulls in it, meaning I want to allow more than one record if bar field is null,

Answer 1

For better or worse, Django considers NULL to be equivalent to NULL for purposes of uniqueness checks. There's really no way around it short of writing your own implementation of the uniqueness check which considers NULL to be unique no matter how many times it occurs in a table.

(and keep in mind that some DB solutions take the same view of NULL, so code relying on one DB's ideas about NULL may not be portable to others)