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Caution!

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mongopersist

A python mongoDB Persistence Backend.

Providing transparent persistence of python objects.

This document outlines the general capabilities of the mongopersist package. mongopersist is a mongoDB storage implementation for persistent Python objects. It is NOT a storage for the ZODB.

The goal of mongopersist is to provide a data manager that serializes objects to mongoDB at transaction boundaries. The mongo data manager is a persistent data manager, which handles events at transaction boundaries (see transaction.interfaces.IDataManager) as well as events from the persistency framework (see persistent.interfaces.IPersistentDataManager).

An instance of a data manager is supposed to have the same life time as the transaction, meaning that it is assumed that you create a new data manager when creating a new transaction:

>>> import transaction

Let's now define a simple persistent object:

>>> import persistent
>>> class Person(persistent.Persistent, ReprMixin):
...
...     def __init__(self, name, phone=None, address=None, friends=None,
...                  visited=(), birthday=None):
...         self.name = name
...         self.address = address
...         self.friends = friends or {}
...         self.visited = visited
...         self.phone = phone
...         self.birthday = birthday
...         self.today = datetime.datetime.now()
...
...     def __str__(self):
...         return self.name

Let's create a new person and store it in mongoDB:

>>> stephan = Person(u'Stephan')
>>> dm.root['stephan'] = stephan

By default, persistent objects are stored in a collection having the Python path of the class. Let's see what got stored in mongoDB:

>>> dumpCollection('__main__.Person')
[{u'_id': ObjectId('51c0571eb25d2b2de8325726'),
  u'address': None,
  u'birthday': None,
  u'friends': {},
  u'name': u'Stephan',
  u'phone': None,
  u'today': datetime.datetime(2013, 6, 18, 14, 48, 30, 970000),
  u'visited': []}]

Let's now add an address for Stephan. Addresses are also persistent objects:

>>> class Address(persistent.Persistent, ReprMixin):
...     _p_mongo_collection = 'address'
...
...     def __init__(self, city, zip):
...         self.city = city
...         self.zip = zip
...
...     def __str__(self):
...         return '%s (%s)' %(self.city, self.zip)
>>> stephan.address = Address('Maynard', '01754')

We need to commit the transaction, to push the data to mongoDB:

>>> transaction.commit()
>>> dumpCollection('address')
[{u'_id': ObjectId('51c05809b25d2b2e4f90cbdd'),
  u'city': u'Maynard',
  u'zip': u'01754'}]

As you can see, even the reference to the Address object looks nice and uses the standard mongoDB reference construct.

>>> dumpCollection('__main__.Person')
[{u'_id': ObjectId('51c05819b25d2b2ea58a4e55'),
  u'address': DBRef(u'address', ObjectId('51c05819b25d2b2ea58a4e58'), u'mongopersist_test'),
  u'birthday': None,
  u'friends': {},
  u'name': u'Stephan',
  u'phone': None,
  u'today': datetime.datetime(2013, 6, 18, 14, 52, 41, 133000),
  u'visited': []}]

But what about arbitrary non-persistent, but picklable, objects? Well, let's create a phone number object for that:

>>> class Phone(ReprMixin):
...
...     def __init__(self, country, area, number):
...         self.country = country
...         self.area = area
...         self.number = number
...
...     def __str__(self):
...         return '%s-%s-%s' %(self.country, self.area, self.number)
>>> stephan = dm.root['stephan']
>>> stephan.phone = Phone('+1', '978', '394-5124')
>>> transaction.commit()
>>> dumpCollection('__main__.Person')
[{u'_id': ObjectId('51c059beb25d2b3157bf5adf'),
  u'address': DBRef(u'address', ObjectId('51c059beb25d2b3157bf5ae2'), u'mongopersist_test'),
  u'birthday': None,
  u'friends': {},
  u'name': u'Stephan',
  u'phone': {u'_py_type': u'__main__.Phone',
             u'area': u'978',
             u'country': u'+1',
             u'number': u'394-5124'},
  u'today': datetime.datetime(2013, 6, 18, 14, 59, 42, 554000),
  u'visited': []}]

Let's now set various attributes:

>>> stephan = dm.root['stephan']
>>> stephan.friends = {'roy': Person(u'Roy Mathew')}
>>> stephan.visited = (u'Germany', u'USA')
>>> stephan.birthday = datetime.date(1980, 1, 25)

Push the data to mongoDB, and dump the results:

>>> transaction.commit()
>>> dumpCollection('__main__.Person')
[{u'_id': ObjectId('4e7ddf12e138237403000000'),
  u'address': DBRef(u'address', ObjectId('4e7ddf12e138237403000000'), u'mongopersist_test'),
  u'birthday': {u'_py_factory': u'datetime.date',
                u'_py_factory_args': [Binary('\x07\xbc\x01\x19', 0)]},
  u'friends': {u'roy': DBRef(u'__main__.Person', ObjectId('4e7ddf12e138237403000000'), u'mongopersist_test')},
  u'name': u'Stephan',
  u'phone': {u'_py_type': u'__main__.Phone',
             u'area': u'978',
             u'country': u'+1',
             u'number': u'394-5124'},
  u'today': datetime.datetime(2011, 10, 1, 9, 45)
  u'visited': [u'Germany', u'USA']},
 {u'_id': ObjectId('4e7ddf12e138237403000000'),
  u'address': None,
  u'birthday': None,
  u'friends': {},
  u'name': u'Roy Mathew',
  u'phone': None,
  u'today': datetime.datetime(2011, 10, 1, 9, 45)
  u'visited': []}]

Of course all properties can be retrieved as python objects:

>>> stephan = dm.root['stephan']
>>> stephan.address
<Address Maynard (01754)>
>>> stephan.address.city
u'Maynard'
>>> stephan.birthday
datetime.date(1980, 1, 25)
>>> stephan.friends
{u'roy': <Person Roy Mathew>}
>>> stephan.phone
<Phone +1-978-394-5124>
>>> stephan.today
datetime.datetime(2011, 10, 1, 9, 45)
>>> stephan.visited
[u'Germany', u'USA']

See src/mongopersist/README.txt and the other txt files in the package for more details.

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