Demonstration of formfield_for_foreignkey method on Django.

admin.py

def formfield_for_foreignkey(self, db_field, request, **kwargs):
    if db_field.name == "usuario":
        usuario_id = request.GET.get('usuario_id', None)
        if usuario_id:
            kwargs['initial'] = usuario_id
    if db_field.name == "psicologo":
        kwargs["queryset"] = User.objects.filter(is_superuser=True)
    return super(EntrevistaAdmin, self).formfield_for_foreignkey(db_field, request, **kwargs)