Hey,

 

I have a model which has a date and a foreign key field. I want a uniqueness 
constraint that each fk can only be used once per month, so Unique(date__year, 
date__month, fk). However, when I use this in my model’s metadata:

 

models.UniqueConstraint(fields=['date__year', 'date__month', 'category'], 
name='date_month_cat_unique')

 

I get an error that the date__year field doesn’t exist. This is a bit strange 
because I use this syntax throughout my app and I also know that such 
constraints are supported by Postgres:

 

create unique index year_month_uq 

  on foo 

  ( extract(year from mydate), 

    extract(month from mydate)

  ) ;

 

As per 
https://dba.stackexchange.com/questions/210736/postgresql-enforcing-unique-constraint-on-date-column-parts

 

What am I doing wrong here? I’m using Django 3 and Postgres.

 

Thanks

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