Database

Plone uses ZODB database. ZODB happily eats any Python object with any attributes - there is no need to write “database schemas” as it is with SQL based systems.

Classes inherit for persistent.Persistent will have all their attributes written to database. Lists and dictionaries will be automatically converted to persistent versions.

Schema based database look-ups

To create schema based database query services, catalogs are used. Please read more about this in chapter Search and indexing.

Data validation

Even though ZODB does not force schema for persistent objects, it is often the best practice to use zope.schema and its FieldProperty decorator to force data validation before writing it to the database.

Example:

from persistent import Persistent
from zope import schema
from zope.interface import Interface
from zope.schema.fieldproperty import FieldProperty


class IMyObject(Interface):
    """ Define *content* of MyObject attributes.

    New attributes can be still added, unless you
    use Python __slots__ mechanism.
    """
    my_bool = schema.Bool(title=u"Define bool", description=u"object.my_bool only accepts boolean values")

class MyObject(Persistent):
    """ Sample persistent object for the IMyObject schema """
    implements(IHeaderBehavior)

    # Force validation of my_bool attribute
    # during the set. FieldProperty will create
    # Python property setter and getter methods
    # which will take care of the validation
    my_bool = FieldProperty(IMyObject["inheri    le"])