django/db/__init__.py

   1 import os
   2 from django.conf import settings
   3 from django.core import signals
   4 from django.core.exceptions import ImproperlyConfigured
   5 from django.utils.functional import curry
   6
   7 __all__ = ('backend', 'connection', 'DatabaseError', 'IntegrityError')
   8
   9 if not settings.DATABASE_ENGINE:
  10     settings.DATABASE_ENGINE = 'dummy'
  11
  12 try:
  13     # Most of the time, the database backend will be one of the official
  14     # backends that ships with Django, so look there first.
  15     _import_path = 'django.db.backends.'
  16     backend = __import__('%s%s.base' % (_import_path, settings.DATABASE_ENGINE), {}, {}, [''])
  17 except ImportError, e:
  18     # If the import failed, we might be looking for a database backend
  19     # distributed external to Django. So we'll try that next.
  20     try:
  21         _import_path = ''
  22         backend = __import__('%s.base' % settings.DATABASE_ENGINE, {}, {}, [''])
  23     except ImportError, e_user:
  24         # The database backend wasn't found. Display a helpful error message
  25         # listing all possible (built-in) database backends.
  26         backend_dir = os.path.join(__path__[0], 'backends')
  27         try:
  28             available_backends = [f for f in os.listdir(backend_dir) if not f.startswith('_') and not f.startswith('.') and not f.endswith('.py') and not f.endswith('.pyc')]
  29         except EnvironmentError:
  30             available_backends = []
  31         available_backends.sort()
  32         if settings.DATABASE_ENGINE not in available_backends:
  33             raise ImproperlyConfigured, "%r isn't an available database backend. Available options are: %s\nError was: %s" % \
  34                 (settings.DATABASE_ENGINE, ", ".join(map(repr, available_backends)), e_user)
  35         else:
  36             raise # If there's some other error, this must be an error in Django itself.
  37
  38 # Convenient aliases for backend bits.
  39 connection = backend.DatabaseWrapper(**settings.DATABASE_OPTIONS)
  40 DatabaseError = backend.DatabaseError
  41 IntegrityError = backend.IntegrityError
  42
  43 # Register an event that closes the database connection
  44 # when a Django request is finished.
  45 def close_connection(**kwargs):
  46     connection.close()
  47 signals.request_finished.connect(close_connection)
  48
  49 # Register an event that resets connection.queries
  50 # when a Django request is started.
  51 def reset_queries(**kwargs):
  52     connection.queries = []
  53 signals.request_started.connect(reset_queries)
  54
  55 # Register an event that rolls back the connection
  56 # when a Django request has an exception.
  57 def _rollback_on_exception(**kwargs):
  58     from django.db import transaction
  59     try:
  60         transaction.rollback_unless_managed()
  61     except DatabaseError:
  62         pass
  63 signals.got_request_exception.connect(_rollback_on_exception)