"""
Illustrates "vertical table" mappings.

A "vertical table" refers to a technique where individual attributes
of an object are stored as distinct rows in a table. The "vertical
table" technique is used to persist objects which can have a varied
set of attributes, at the expense of simple query control and brevity.
It is commonly found in content/document management systems in order
to represent user-created structures flexibly.

Two variants on the approach are given.  In the second, each row
references a "datatype" which contains information about the type of
information stored in the attribute, such as integer, string, or date.


Example::

    shrew = Animal(u'shrew')
    shrew[u'cuteness'] = 5
    shrew[u'weasel-like'] = False
    shrew[u'poisonous'] = True

    session.add(shrew)
    session.flush()

    q = (session.query(Animal).
         filter(Animal.facts.any(
           and_(AnimalFact.key == u'weasel-like',
                AnimalFact.value == True))))
    print 'weasel-like animals', q.all()

.. autosource::

"""