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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