Self Many2Many Relationship duplicate key value violates unique constraint

[simone]

In the testapp example, Author.friends doesn't permit to relate an author with himself.

Classic Author (with no CFP) works.

Observation:
MayToMany in django assume that symmetrical=True,
I think there is an check in the django code for this unique constraint to evolve for the composite keys.

this is the exception:

IntegrityError at /admin/sample/author/'Simone'-'33'/
duplicate key value violates unique constraint "sample_author_friends_from_author_name_from_author_age_to_a_key"
DETAIL: Key (from_author_name, from_author_age, to_author_name, to_author_age)=(Simone, 33, Simone, 33) already exists.