def _ensure_backend_available(cls, url):
url = sa_url.make_url(str(url))
try:
eng = sqlalchemy.create_engine(url)
except ImportError as i_e:
# SQLAlchemy performs an "import" of the DBAPI module
# within create_engine(). So if ibm_db_sa, cx_oracle etc.
# isn't installed, we get an ImportError here.
LOG.info("The %(dbapi)s backend is unavailable: %(err)s",
dict(dbapi=url.drivername, err=i_e))
raise exception.BackendNotAvailable(
"Backend '%s' is unavailable: No DBAPI installed" %
url.drivername)
else:
try:
conn = eng.connect()
except sqlalchemy.exc.DBAPIError as d_e:
# upon connect, SQLAlchemy calls dbapi.connect(). This
# usually raises OperationalError and should always at
# least raise a SQLAlchemy-wrapped DBAPI Error.
LOG.info("The %(dbapi)s backend is unavailable: %(err)s",
dict(dbapi=url.drivername, err=d_e))
raise exception.BackendNotAvailable(
"Backend '%s' is unavailable: Could not connect" %
url.drivername)
else:
conn.close()
return eng
def backend_for_database_type(cls, database_type):
"""Return the ``Backend`` for the given database type.
"""
try:
backend = cls.backends_by_database_type[database_type]
except KeyError:
raise exception.BackendNotAvailable(database_type)
else:
return backend._verify()
def backend_for_database_type(cls, database_type):
"""Return and verify the ``Backend`` for the given database type.
Creates the engine if it does not already exist and raises
``BackendNotAvailable`` if it cannot be produced.
:return: a base ``Engine`` that allows provisioning of databases.
:raises: ``BackendNotAvailable``, if an engine for this backend
cannot be produced.
"""
try:
backend = cls.backends_by_database_type[database_type]
except KeyError:
raise exception.BackendNotAvailable(database_type)
else:
return backend._verify()
def _verify(self):
"""Verify that this ``Backend`` is available and provisionable.
:return: this ``Backend``
:raises: ``BackendNotAvailable`` if the backend is not available.
"""
if not self.verified:
try:
eng = self._ensure_backend_available(self.url)
except exception.BackendNotAvailable:
raise
else:
self.engine = eng
finally:
self.verified = True
if self.engine is None:
raise exception.BackendNotAvailable(self.database_type)
return self
