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
133 lines
3.3 KiB
ReStructuredText
133 lines
3.3 KiB
ReStructuredText
=======
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Usage
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=======
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To use oslo.db in a project:
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Session Handling
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================
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Session handling is achieved using the :mod:`oslo_db.sqlalchemy.enginefacade`
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system. This module presents a function decorator as well as a
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context manager approach to delivering :class:`.Session` as well as
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:class:`.Connection` objects to a function or block.
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Both calling styles require the use of a context object. This object may
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be of any class, though when used with the decorator form, requires
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special instrumentation.
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The context manager form is as follows:
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.. code:: python
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from oslo_db.sqlalchemy import enginefacade
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class MyContext(object):
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"User-defined context class."
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def some_reader_api_function(context):
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with enginefacade.reader.using(context) as session:
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return session.query(SomeClass).all()
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def some_writer_api_function(context, x, y):
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with enginefacade.writer.using(context) as session:
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session.add(SomeClass(x, y))
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def run_some_database_calls():
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context = MyContext()
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results = some_reader_api_function(context)
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some_writer_api_function(context, 5, 10)
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The decorator form accesses attributes off the user-defined context
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directly; the context must be decorated with the
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:func:`oslo_db.sqlalchemy.enginefacade.transaction_context_provider`
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decorator. Each function must receive the context as the first
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positional argument:
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.. code:: python
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from oslo_db.sqlalchemy import enginefacade
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@enginefacade.transaction_context_provider
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class MyContext(object):
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"User-defined context class."
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@enginefacade.reader
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def some_reader_api_function(context):
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return context.session.query(SomeClass).all()
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@enginefacade.writer
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def some_writer_api_function(context, x, y):
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context.session.add(SomeClass(x, y))
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def run_some_database_calls():
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context = MyContext()
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results = some_reader_api_function(context)
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some_writer_api_function(context, 5, 10)
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The scope of transaction and connectivity for both approaches is managed
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transparently. The configuration for the connection comes from the standard
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:obj:`oslo_config.cfg.CONF` collection. Additional configurations can be
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established for the enginefacade using the
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:func:`oslo_db.sqlalchemy.enginefacade.configure` function, before any use of
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the database begins:
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.. code:: python
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from oslo_db.sqlalchemy import enginefacade
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enginefacade.configure(
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sqlite_fk=True,
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max_retries=5,
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mysql_sql_mode='ANSI'
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)
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Base class for models usage
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===========================
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.. code:: python
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from oslo.db import models
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class ProjectSomething(models.TimestampMixin,
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models.ModelBase):
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id = Column(Integer, primary_key=True)
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...
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DB API backend support
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======================
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.. code:: python
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from oslo.config import cfg
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from oslo.db import api as db_api
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_BACKEND_MAPPING = {'sqlalchemy': 'project.db.sqlalchemy.api'}
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IMPL = db_api.DBAPI.from_config(cfg.CONF, backend_mapping=_BACKEND_MAPPING)
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def get_engine():
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return IMPL.get_engine()
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def get_session():
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return IMPL.get_session()
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# DB-API method
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def do_something(somethind_id):
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return IMPL.do_something(somethind_id)
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