Filter elements of a model by a calculated field NOT possible

[KenWhitesell]

Correct.

@SeritiAymen

Bdc.date_paiment

Bdc is a model. It’s not an instance of a model. That means that a reference to Bdc.date_paiment is a reference to a field, and not a value in a field.

You can’t do what you want to do this way.
That sort of calculation within the query must be done with a query expression.

See:

• Query Expressions | Django documentation | Django
  and
• Database Functions | Django documentation | Django