old_contents: from typing import Optional
  
  from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  from django.db import connections
  from django.db.models import Manager
  
  from psqlextra.query import PostgresQuerySet
  
  
  class PostgresManager(Manager.from_queryset(PostgresQuerySet)):
      """Adds support for PostgreSQL specifics."""
  
      use_in_migrations = True
  
      def __init__(self, *args, **kwargs):
          """Initializes a new instance of :see:PostgresManager."""
  
          super().__init__(*args, **kwargs)
  
          # make sure our back-end is set in at least one db and refuse to proceed
          # if it's not set
          def has_pqlextra_backend():
              for db_alias, db_settings in settings.DATABASES.items():
                  db_backend = db_settings['ENGINE']
                  if "psqlextra" in db_backend:
                      return True
              return False
  
          if not has_pqlextra_backend():
              raise ImproperlyConfigured(
                  (
                      "Could not locate the 'psqlextra.backend'. "
                      "django-postgres-extra cannot function without "
                      "the 'psqlextra.backend'. Set DATABASES.ENGINE."
                  )
              )
  
      def truncate(
          self, cascade: bool = False, using: Optional[str] = None
      ) -> None:
          """Truncates this model/table using the TRUNCATE statement.
  
          This DELETES ALL ROWS. No signals will be fired.
  
          See: https://www.postgresql.org/docs/9.1/sql-truncate.html
  
          Arguments:
              cascade:
                  Whether to delete dependent rows. If set to
                  False, an error will be raised if there
                  are rows in other tables referencing
                  the rows you're trying to delete.
          """
  
          connection = connections[using or "default"]
          table_name = connection.ops.quote_name(self.model._meta.db_table)
  
          with connection.cursor() as cursor:
              sql = "TRUNCATE TABLE %s" % table_name
              if cascade:
                  sql += " CASCADE"
  
              cursor.execute(sql)
  
new_contents: from typing import Optional
  
  from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  from django.db import connections
  from django.db.models import Manager
  
  from psqlextra.query import PostgresQuerySet
  
  
  class PostgresManager(Manager.from_queryset(PostgresQuerySet)):
      """Adds support for PostgreSQL specifics."""
  
      use_in_migrations = True
  
      def __init__(self, *args, **kwargs):
          """Initializes a new instance of :see:PostgresManager."""
  
          super().__init__(*args, **kwargs)
  
          # make sure our back-end is set in at least one db and refuse to proceed
          has_psqlextra_backend = any(
              [
                  db_settings
                  for db_settings in settings.DATABASES.values()
                  if "psqlextra" in db_settings["ENGINE"]
              ]
          )
  
          if not has_psqlextra_backend:
              raise ImproperlyConfigured(
                  (
                      "Could not locate the 'psqlextra.backend'. "
                      "django-postgres-extra cannot function without "
                      "the 'psqlextra.backend'. Set DATABASES.ENGINE."
                  )
              )
  
      def truncate(
          self, cascade: bool = False, using: Optional[str] = None
      ) -> None:
          """Truncates this model/table using the TRUNCATE statement.
  
          This DELETES ALL ROWS. No signals will be fired.
  
          See: https://www.postgresql.org/docs/9.1/sql-truncate.html
  
          Arguments:
              cascade:
                  Whether to delete dependent rows. If set to
                  False, an error will be raised if there
                  are rows in other tables referencing
                  the rows you're trying to delete.
          """
  
          connection = connections[using or "default"]
          table_name = connection.ops.quote_name(self.model._meta.db_table)
  
          with connection.cursor() as cursor:
              sql = "TRUNCATE TABLE %s" % table_name
              if cascade:
                  sql += " CASCADE"
  
              cursor.execute(sql)
  
subject: Simplify check that verifies that at least one DB is using the back-end