django1/django/db/__init__.py

from django.core import signals
from django.db.utils import (
    DEFAULT_DB_ALIAS, DJANGO_VERSION_PICKLE_KEY, ConnectionHandler,
    ConnectionRouter, DatabaseError, DataError, Error, IntegrityError,
    InterfaceError, InternalError, NotSupportedError, OperationalError,
    ProgrammingError,
)
from django.utils.connection import ConnectionProxy

__all__ = [
    'connection', 'connections', 'router', 'DatabaseError', 'IntegrityError',
    'InternalError', 'ProgrammingError', 'DataError', 'NotSupportedError',
    'Error', 'InterfaceError', 'OperationalError', 'DEFAULT_DB_ALIAS',
    'DJANGO_VERSION_PICKLE_KEY',
]

connections = ConnectionHandler()

router = ConnectionRouter()

# For backwards compatibility. Prefer connections['default'] instead.
connection = ConnectionProxy(connections, DEFAULT_DB_ALIAS)


# Register an event to reset saved queries when a Django request is started.
def reset_queries(**kwargs):
    for conn in connections.all():
        conn.queries_log.clear()


signals.request_started.connect(reset_queries)


# Register an event to reset transaction state and close connections past
# their lifetime.
def close_old_connections(**kwargs):
    for conn in connections.all():
        conn.close_if_unusable_or_obsolete()


signals.request_started.connect(close_old_connections)
signals.request_finished.connect(close_old_connections)