fdbd928b1f
This module presents a replacement for the EngineFacade system. At the center is the oslo.db.sqlalchemy.enginefacade module, which when imported, provides decorators and context managers which perform all database and ORM connectivity functions transparently. The docstrings as well as the blueprint provide an introduction. The patch includes a refactoring of sqlalchemy/session.py into three dependent modules engines.py, orm.py and enginefacade.py. This is to maintain a non-cyclical import structure as well as to maintain the import behavior of oslo.db overall, as some projects such as glance currently have dependencies on this structure. There is also a slimming down and attempt at modernizing some very old documentation in session.py. The enginefacade system should be preferred moving forward. Implements: blueprint make-enginefacade-a-facade Change-Id: I9a3d0c26bb727eb2c0bd823b9a12fde57cc7c9c3
251 lines
7.3 KiB
Python
251 lines
7.3 KiB
Python
# Copyright 2010 United States Government as represented by the
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# Administrator of the National Aeronautics and Space Administration.
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# All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License"); you may
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# not use this file except in compliance with the License. You may obtain
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# a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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# License for the specific language governing permissions and limitations
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# under the License.
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"""DB related custom exceptions.
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Custom exceptions intended to determine the causes of specific database
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errors. This module provides more generic exceptions than the database-specific
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driver libraries, and so users of oslo.db can catch these no matter which
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database the application is using. Most of the exceptions are wrappers. Wrapper
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exceptions take an original exception as positional argument and keep it for
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purposes of deeper debug.
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Example::
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try:
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statement(arg)
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except sqlalchemy.exc.OperationalError as e:
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raise DBDuplicateEntry(e)
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This is useful to determine more specific error cases further at execution,
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when you need to add some extra information to an error message. Wrapper
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exceptions takes care about original error message displaying to not to loose
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low level cause of an error. All the database api exceptions wrapped into
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the specific exceptions provided belove.
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Please use only database related custom exceptions with database manipulations
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with `try/except` statement. This is required for consistent handling of
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database errors.
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"""
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import six
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from oslo_db._i18n import _
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class DBError(Exception):
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"""Base exception for all custom database exceptions.
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:kwarg inner_exception: an original exception which was wrapped with
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DBError or its subclasses.
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"""
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def __init__(self, inner_exception=None):
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self.inner_exception = inner_exception
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super(DBError, self).__init__(six.text_type(inner_exception))
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class DBDuplicateEntry(DBError):
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"""Duplicate entry at unique column error.
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Raised when made an attempt to write to a unique column the same entry as
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existing one. :attr: `columns` available on an instance of the exception
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and could be used at error handling::
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try:
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instance_type_ref.save()
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except DBDuplicateEntry as e:
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if 'colname' in e.columns:
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# Handle error.
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:kwarg columns: a list of unique columns have been attempted to write a
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duplicate entry.
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:type columns: list
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:kwarg value: a value which has been attempted to write. The value will
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be None, if we can't extract it for a particular database backend. Only
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MySQL and PostgreSQL 9.x are supported right now.
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"""
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def __init__(self, columns=None, inner_exception=None, value=None):
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self.columns = columns or []
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self.value = value
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super(DBDuplicateEntry, self).__init__(inner_exception)
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class DBConstraintError(DBError):
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"""Check constraint fails for column error.
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Raised when made an attempt to write to a column a value that does not
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satisfy a CHECK constraint.
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:kwarg table: the table name for which the check fails
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:type table: str
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:kwarg check_name: the table of the check that failed to be satisfied
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:type check_name: str
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"""
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def __init__(self, table, check_name, inner_exception=None):
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self.table = table
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self.check_name = check_name
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super(DBConstraintError, self).__init__(inner_exception)
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class DBReferenceError(DBError):
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"""Foreign key violation error.
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:param table: a table name in which the reference is directed.
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:type table: str
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:param constraint: a problematic constraint name.
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:type constraint: str
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:param key: a broken reference key name.
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:type key: str
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:param key_table: a table name which contains the key.
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:type key_table: str
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"""
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def __init__(self, table, constraint, key, key_table,
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inner_exception=None):
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self.table = table
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self.constraint = constraint
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self.key = key
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self.key_table = key_table
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super(DBReferenceError, self).__init__(inner_exception)
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class DBDeadlock(DBError):
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"""Database dead lock error.
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Deadlock is a situation that occurs when two or more different database
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sessions have some data locked, and each database session requests a lock
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on the data that another, different, session has already locked.
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"""
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def __init__(self, inner_exception=None):
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super(DBDeadlock, self).__init__(inner_exception)
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class DBInvalidUnicodeParameter(Exception):
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"""Database unicode error.
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Raised when unicode parameter is passed to a database
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without encoding directive.
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"""
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message = _("Invalid Parameter: "
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"Encoding directive wasn't provided.")
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class DbMigrationError(DBError):
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"""Wrapped migration specific exception.
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Raised when migrations couldn't be completed successfully.
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"""
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def __init__(self, message=None):
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super(DbMigrationError, self).__init__(message)
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class DBConnectionError(DBError):
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"""Wrapped connection specific exception.
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Raised when database connection is failed.
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"""
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pass
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class DBDataError(DBError):
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"""Raised for errors that are due to problems with the processed data.
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E.g. division by zero, numeric value out of range, incorrect data type, etc
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"""
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class InvalidSortKey(Exception):
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"""A sort key destined for database query usage is invalid."""
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message = _("Sort key supplied was not valid.")
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class ColumnError(Exception):
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"""Error raised when no column or an invalid column is found."""
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class BackendNotAvailable(Exception):
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"""Error raised when a particular database backend is not available
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within a test suite.
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"""
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class RetryRequest(Exception):
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"""Error raised when DB operation needs to be retried.
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That could be intentionally raised by the code without any real DB errors.
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"""
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def __init__(self, inner_exc):
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self.inner_exc = inner_exc
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class NoEngineContextEstablished(AttributeError):
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"""Error raised for non-present enginefacade attribute access.
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This applies to the ``session`` and ``connection`` attributes
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of a user-defined context and/or RequestContext object, when they
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are accessed outside of the scope of an enginefacade decorator
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or context manager.
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The exception is a subclass of AttributeError so that
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normal Python missing attribute behaviors are maintained, such
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as support for ``getattr(context, 'session', None)``.
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"""
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class NotSupportedWarning(Warning):
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"""Warn that an argument or call that was passed is not supported.
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This subclasses Warning so that it can be filtered as a distinct
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category.
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.. seealso::
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https://docs.python.org/2/library/warnings.html
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"""
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class OsloDBDeprecationWarning(DeprecationWarning):
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"""Issued per usage of a deprecated API.
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This subclasses DeprecationWarning so that it can be filtered as a distinct
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category.
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.. seealso::
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https://docs.python.org/2/library/warnings.html
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"""
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