Using MongoDB

TurboGears supports MongoDB out of the box by using the Ming ORM. Ming was made to look like SQLAlchemy, so if you are proficient with SQLAlchemy and MongoDB it should be easy for you to get used to the Ming query language. This also makes easy to port a TurboGears SQLAlchemy based application to MongoDB.

QuickStarting with MongoDB

To create a project using MongoDB you just need to pass the --ming option to the gearbox quickstart command.

$ gearbox quickstart --ming myproj

The quickstarted project will provide an authentication and authorization layer like the one that is provided for the SQLAlchemy version. This means that you will have the same users and groups you had on the standard quickstarted project and also that all the predicates to check for authorization should work like before.

The main difference is that you won’t be able to use the application without having a running MongoDB database on the local machine.

By default the application will try to connect to a server on port 27017 on local machine using a database that has the same name of your package.

This can be changed by editing the development.ini file:

ming.url = mongodb://localhost:27017/myproject

Now that everything is in place to start using MongoDB as your database server you just need to proceed the usual way by filling your database.

$ gearbox setup-app

The quickstart command from above will create the authentication collections and setup a default user/password for you:

user: manager
password: managepass

Working With Ming

If you don’t know how Ming works at all, please take a few minutes to read over the Ming documentation as this documentation will only cover Ming integration with TurboGears.

Your quickstarted project will have a subpackage called model, made up of the following files:

  • This is where the database access is set up. Your collections should be imported into this module, and you’re highly encouraged to define them in a separate module - entities, for example.
  • This file defines the session of your database connection. By default TurboGears will use a Session object with multi-threading support. You will usually need to import this each time you have to declare a MappedClass to specify the session that has to be used to perform queries.
  • This file will be created if you enabled authentication and authorization in the quickstart. It defines three collections repoze.who relies on: User (for the registered members in your website and the groups they belong to), Group (for groups of users) and Permission (a permission granted to one or more groups).

Defining Your Own Collections

By default TurboGears configures Ming in Declarative mode. This is similar to the SQLAlchemy declarative support and needs each model to inherit from the MappedClass class.

The tables defined by the quickstart in model/ are based on the declarative method, so you may want to check it out to see how columns are defined for these tables.

To see how to define your models refer to Ming UserGuide

Once you have defined your collections in a separate module in the model package, they should be imported from model/ So the end of this file would look like this:

# Import your model modules here.
from auth import User, Permission
# Say you defined these three classes in the 'movies'
# module of your 'model' package.
from movies import Movie, Actor, Director

Indexing Support

TurboGears supports also automatic indexing of MongoDB fields. If you want to guarantee that a field is unique or indexed you just have to specify the unique_indexes or indexes variables for the __mongometa__ attribute of the mapped class.

class Permission(MappedClass):
    class __mongometa__:
        session = DBSession
        name = 'tg_permission'
        unique_indexes = [('permission_name',),]

TurboGears will ensure indexes for your each time the application is started, this is performed inside the init_model function.

Indexes are covered in detail in Ming Indexing Documentation.

Handling Relationships

Ming comes with support to one-to-many, many-to-one and many-to-many Relations they provide an easy to use access to related objects. The fact that this relation is read only isn’t a real issue as the related objects will have a ForeignIdProperty which can be changed to add or remove objects to the relation.

TurboGears comes with a bunc of Many-to-Many relations already defined so you can see them in action in the Permission and Group classes:

class Group(MappedClass):
    Group definition.
    class __mongometa__:
        session = DBSession
        name = 'tg_group'
        unique_indexes = [('group_name',),]

    _id = FieldProperty(s.ObjectId)
    group_name = FieldProperty(s.String)
    display_name = FieldProperty(s.String)

    permissions = RelationProperty('Permission')

class Permission(MappedClass):
    Permission definition.
    class __mongometa__:
        session = DBSession
        name = 'tg_permission'
        unique_indexes = [('permission_name',),]

    _id = FieldProperty(s.ObjectId)
    permission_name = FieldProperty(s.String)
    description = FieldProperty(s.String)

    _groups = ForeignIdProperty(Group, uselist=True)
    groups = RelationProperty(Group)

You can see the permissions and groups properties that provide the interface to the relation and the _groups property that stores ids of groups related to each Permission in a mongodb array.

In this case each user will have one or more groups stored with their group_name inside the Permission._groups array. Accessing Permission.groups will provide a list of the groups the user is part of.

For a complete coverage of Relationships with Ming refer to Ming Relations guide.

Custom Properties

There are cases when you will want to adapt a value from the database before loading and storing it. A simple example of this case is the password field, this will probably be encrypted with some kind of algorithm which has to be applied before saving the field itself.

To handle those cases TurboGears Ming allows subclassing field property to declare CustomProperties. This provides a way to hook two functions which have to be called before storing and retrieving the value to adapt it through Python Descriptors Protocol:

class PasswordProperty(FieldProperty):
    def _hash_password(cls, password):
        salt = sha256()
        salt = salt.hexdigest()

        hash = sha256()
        # Make sure password is a str because we cannot hash unicode objects
        hash.update((password + salt).encode('utf-8'))
        hash = hash.hexdigest()

        password = salt + hash

        # Make sure the hashed password is a unicode object at the end of the
        # process because SQLAlchemy _wants_ unicode objects for Unicode cols
        password = password.decode('utf-8')

        return password

    def __set__(self, instance, value):
        value = self._hash_password(value)
        return FieldProperty.__set__(self, instance, value)

In the previous example the password property automatically hashed each time a new value is assigned to the property. That is performed by PasswordProperty.__set__ which calls _hash_password before calling FieldProperty.__set__ which actually saves the password.

For additional details on working with custom properties refer to CustomProperties Ming Documentation.