models 0.9.1

Python models for schema-less databases.

Models is a lightweight framework for mapping Python classes to schema-less databases. It is not an ORM as it doesn’t map existing schemata to Python objects but instead defines them on a higher layer built upon a schema-less storage (key/value or document-oriented). You define models as a valuable subset of the whole database and work with only certain parts of existing entities – the parts you need.

Installation

$ sudo easy_install models

You will also need to install pyrant to enable the Tokyo Tyrant backend. In order to use Models with Tokyo Cabinet (i.e. directly, not through Tyrant) you will also need a recent snapshot of the tc from github along with pyrant. You might want to use another library (or libraries) with Models.

Backends

Currently Tokyo Cabinet and Tokyo Tyrant backends are included. Any other backend can be more or less easily created by wrapping existing bindings in Storage and Query classes which can loosely follow existing guidelines.

The Models library does not impose a strict API, it only recommends one. In fact, you will only need to have the backend return a query instance (even bindings’ native one) and wrap the results in given model’s objects. See models.backends.tyrant for examples.

Usage

Not surprising to those who had ever used an ORM:

class Country(Model):
    name = Property(unicode)    # any Python type; default is unicode

    def __unicode__(self):
        return self.name

    class Meta:
        must_have = {'type': 'country'}


class Person(Model):
    first_name = Property(required=True)
    last_name = Property(required=True)
    gender = Property()
    birth_date = Date()
    birth_place = Property(Country)    # reference to another model

    def __unicode__(self):
        return self.full_name    # full_name is a dynamic attr, see below

    @property
    def age(self):
        return (datetime.datetime.now().date() - self.birth_date).days / 365

    @property
    def full_name(self):
        return '%s %s' % (self.first_name, self.last_name)

    class Meta:
        must_have = {'is_person': True}

The interesting part is the Meta subclass. It contains a must_have attribute which actually binds the model to a subset of data in the storage. {'is_person': True} states that a data row/document/… must contain a bool field is_person with value True. You can easily define any other query conditions. If you create an empty Person instance, it will have all the “must haves” pre-filled.

Now let’s try these models with a Tokyo Cabinet database:

>>> storage = models.get_storage(backend='models.backends.tokyo_cabinet',
...                              kind='TABLE', path='test.tct')
>>> guido = Person.query(storage).filter(first_name='Guido')[0]
>>> guido
<Person Guido van Rossum>
>>> guido.first_name
Guido
>>> guido.birth_date
datetime.date(1960, 1, 31)
>>> guido.age
49
>>> guido.birth_place = Country(name="Netherlands")
>>> guido.save(storage)
>>> guido.birth_place
<Country Netherlands>

…and so on.

Note that relations are supported out of the box.

Switching backends

The Models library provides backends for both Tokyo Cabinet (models.backends.tokyo_cabinet) and Tokyo Tyrant (models.backends.tokyo_tyrant). You can choose the TC backend to use the DB file directly, or switch to the TT backend to access the same file through the manager. The first option is great for development and some other cases where you would use SQLite; the second option is important for most production environments where multiple connections are expected. The good news is that there’s no more import and export, dump/load sequences, create/alter/drop and friends. Having tested the application against the database storage.tct with Cabinet backend, just run ttserver storage.tct and switch the backend config.

Let’s create our application:

import models
import settings
import schemata     # the actual models described above (Country and Person)

storage = models.get_storage(settings.DATABASE)

print schemata.Person.query(storage)   # prints all Person objects from DB

Now define settings for both backends (settings.py):

# direct access to the database (simple, not scalable)
TOKYO_CABINET_DATABASE = {
    'backend': 'models.backends.tokyo_cabinet',
    'kind': 'TABLE',
    'path': 'storage.tct',
}

# access through the Tyrant manager (needs daemon, scalable)
TOKYO_TYRANT_DATABASE = {
    'backend': 'models.backends.tokyo_tyrant',
    'host': 'localhost',
    'port': '1978',
}

# this is the *only* line you need to change in order to change the backend
DATABASE = TOKYO_CABINET_DATABASE

Author

Originally written by Andrey Mikhaylenko in 2009.

See the file AUTHORS for a complete authors list of this application.

Please feel free to submit patches, report bugs or request features:

http://bitbucket.org/neithere/models/issues/

Licensing

Models is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

Models is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with Models. If not, see <http://gnu.org/licenses/>.