Metadata-Version: 2.1
Name: polydatum
Version: 0.9.1
Summary: An encapsulated persistance layer for Python
Home-page: https://github.com/plynth/polydatum
Author: Mike Thornton
Author-email: six8@devdetails.com
License: MIT
Description: =========
        Polydatum
        =========
        
        .. image:: https://secure.travis-ci.org/plynth/polydatum.png
            :target: http://travis-ci.org/plynth/polydatum
            :alt: Build Status
        
        A Python encapsulated persistence layer for supporting many data access layers.
        
        ---------
        Changelog
        ---------
        
        0.9.1
        =====
        
        * Un-pinned third-party libraries
        
        0.9.0
        =====
        
        * Added support for Python 3.6+
        
        
        0.8.4
        =====
        
        * Added context middleware
        * Added read only Meta for context
        * First pass at removing LocalProxy magic to make it easier to integrate with other frameworks
        * Made it so you can use simple generator functions for resources
        * Added replace service/resource and made it hard to accidentally register on top of an existing one
        * Simplified exception handling on DataAccessContext so that only in-context or middleware exceptions are raised. Resource exit exceptions are suppressed.
        
        Bug Fixes
        ---------
        
        * Fixed a bug that prevented usage of a resource in __exit__
        
        ----------
        Components
        ----------
        
        DataManager
        ===========
        
        The DataManager is the central object of Polydatum. It is a top-level registry for
        Services, Resources, and Middleware. Typically an application has one DataManager
        per process. The DataManager also manages Contexts and gives access the DAL.
        
        
        Context
        =======
        
        The Context contains the current state for the active request. It also provides
        access to Resources. When used in an HTTP framework typically one context is
        created at the start of the HTTP request and it ends before the HTTP response
        is sent.
        
        When used with task managers such as Celery, the Context is created at the
        start of a task and ends before the task result is returned.
        
        
        DAL
        ===
        
        The DAL is the "Data Access Layer". The DAL is the registry for all Services.
        To make call a method on a Service, you start with the DAL.
        
        ::
        
            result = dal.someservice.somemethod()
        
        
        Service
        =======
        
        Services encapsulate business logic and data access. They are the Controller of
        MVC-like applications. Services can be nested within other services.
        
        ::
        
            dal.register_services(
                someservice=SomeService().register_services(
                    subservice=SubService()
                )
            )
        
            result = dal.someservice.subservice.somemethod()
        
        
        Meta
        ====
        
        Meta is data about the context and usually includes things like the active
        user or HTTP request. Meta is read only and can not be modified inside the
        context.
        
        ::
        
            class UserService(Service):
                def get_user(self):
                    return self._ctx.meta.user
        
            dm = DataManager()
            dm.register_services(users=UserService())
        
            with dm.context(meta={'user': 'bob'}) as ctx:
                assert ctx.dal.test.get_user() == 'bob'
        
        
        Resource
        ========
        
        Resources are on-demand access to data backends such as SQL databases, key
        stores, and blob stores. Resources have a setup and teardown phase. Resources
        are only initialized and setup when they are first accessed within a context.
        This lazy loading ensures that only the Resources that are needed for a
        particular request are initialized.
        
        The setup/teardown phases are particularly good for checking connections out
        from a connection pool and checking them back in at the end of the request.
        
        ::
        
            def db_pool(context):
                conn = db.checkout_connection()
                yield conn
                db.checkin_connection(conn)
        
            class ItemService(Service):
                def get_item(self, id):
                    return self._data_manager.db.query(
                        'SELECT * FROM table WHERE id={id}',
                        id=id
                    )
        
            dm = DataManager()
            dm.register_services(items=ItemService())
            dm.register_resources(db=db_pool)
        
            with dm.dal() as dal:
                item = dal.items.get_item(1)
        
        
        Middleware
        ==========
        
        Middleware have a setup and teardown phase for each context. They are
        particularly useful for managing transactions or error handling.
        
        Context Middleware may only see and modify the Context. With the
        Context, Context Middleware can gain access to Resources.
        
        ::
        
            def transaction_middleware(context):
                trans = context.db_resource.new_transaction()
                trans.start()
                try:
                    yield trans
                except:
                    trans.abort()
                else:
                    trans.commit()
        
            dm = DataManager()
            dm.register_context_middleware(transaction_middleware)
        
        
        ----------
        Principles
        ----------
        
        - Methods that get an object should return `None` if an object can not be found.
        - Methods that rely on an object existing to work (such as `create` that relies
          on a parent object) should raise `NotFound` if the parent object does not exist.
        - All data access (SQL, MongoDB, Redis, S3, etc) must be done within a Service.
        
        
        --------------
        Considerations
        --------------
        
        Middleware vs Resource
        ======================
        
        A Resource is created on demand. It's purpose is to create a needed resource
        for a request and clean it up when done. It is created inside the context (and possibly
        by middleware). Errors that occur during Resource teardown are suppressed.
        
        Middleware is ran on every context. It is setup before the context is active and
        torndown before resources are torndown. It's purpose is to do setup/teardown within
        the context. Errors that occur in-context are propagated to middleware. Errors that
        occur in middleware are also propagated.
        
        
        Testing
        -------
        
        To run tests you'll need to install the test requirements:
        
            pip install -e .
            pip install -r src/tests/requirements.txt
        
        Run tests:
        
            cd src/tests && py.test
        
        
Keywords: orm,persistence
Platform: UNKNOWN
Classifier: Programming Language :: Python
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: MIT License
Classifier: Natural Language :: English
Classifier: Topic :: Software Development :: Libraries :: Python Modules
Classifier: Programming Language :: Python
Classifier: Programming Language :: Python :: 2.7
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.6
Classifier: Programming Language :: Python :: 3.7
Description-Content-Type: text/x-rst
