class First:
    route_app_labels = {'csv', 'contenttypes'}

    def db_for_read(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return 'default'
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return 'default'
        return None

    def allow_relation(self, obj1, obj2, **hints):
        if (
            obj1._meta.app_label in self.route_app_labels or
            obj2._meta.app_label in self.route_app_labels
        ):
           return 'default'
        return None



class Second:
    route_app_labels = {'csv', 'contenttypes'}

    def db_for_read(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return 'CSV_file_DB'
        return None

    def db_for_write(self, model, **hints):
        if model._meta.app_label in self.route_app_labels:
            return 'CSV_file_DB'
        return None

    def allow_relation(self, obj1, obj2, **hints):
        if (
            obj1._meta.app_label in self.route_app_labels or
            obj2._meta.app_label in self.route_app_labels
        ):
           return 'CSV_file_DB'
        return None

