"""
Illustrates how to embed `dogpile.cache <http://dogpilecache.readthedocs.org/>`_
functionality within
the :class:`.Query` object, allowing full cache control as well as the
ability to pull "lazy loaded" attributes from long term cache
as well.

.. versionchanged:: 0.8 The example was modernized to use
   dogpile.cache, replacing Beaker as the caching library in
   use.

In this demo, the following techniques are illustrated:

* Using custom subclasses of :class:`.Query`
* Basic technique of circumventing Query to pull from a
  custom cache source instead of the database.
* Rudimental caching with dogpile.cache, using "regions" which allow
  global control over a fixed set of configurations.
* Using custom :class:`.MapperOption` objects to configure options on
  a Query, including the ability to invoke the options
  deep within an object graph when lazy loads occur.

E.g.::

    # query for Person objects, specifying cache
    q = Session.query(Person).options(FromCache("default"))

    # specify that each Person's "addresses" collection comes from
    # cache too
    q = q.options(RelationshipCache(Person.addresses, "default"))

    # query
    print q.all()

To run, both SQLAlchemy and dogpile.cache must be
installed or on the current PYTHONPATH. The demo will create a local
directory for datafiles, insert initial data, and run. Running the
demo a second time will utilize the cache files already present, and
exactly one SQL statement against two tables will be emitted - the
displayed result however will utilize dozens of lazyloads that all
pull from cache.

The demo scripts themselves, in order of complexity, are run as Python
modules so that relative imports work::

   python -m examples.dogpile_caching.helloworld

   python -m examples.dogpile_caching.relationship_caching

   python -m examples.dogpile_caching.advanced

   python -m examples.dogpile_caching.local_session_caching


Listing of files:

    environment.py - Establish the Session, a dictionary
    of "regions", a sample cache region against a .dbm
    file, data / cache file paths, and configurations,
    bootstrap fixture data if necessary.

    caching_query.py - Represent functions and classes
    which allow the usage of Dogpile caching with SQLAlchemy.
    Introduces a query option called FromCache.

    model.py - The datamodel, which represents Person that has multiple
    Address objects, each with PostalCode, City, Country

    fixture_data.py - creates demo PostalCode, Address, Person objects
    in the database.

    helloworld.py - the basic idea.

    relationship_caching.py - Illustrates how to add cache options on
    relationship endpoints, so that lazyloads load from cache.

    advanced.py - Further examples of how to use FromCache.  Combines
    techniques from the first two scripts.

    local_session_caching.py - Grok everything so far ?   This example
    creates a new dogpile.cache backend that will persist data in a dictionary
    which is local to the current session.   remove() the session
    and the cache is gone.

"""