archetypes.schemaextender 2.0.1

Introduction
============

This package allows you to modify an Archetypes schema, using simple
adapters. This can be used to add new fields, reorder fields and fieldsets
or make other changes.

The most common use of schema extension is to allow add-on products to
enhance standard Plone content types, for example by adding an option
that can be set to toggle special behaviour.

schemaextender hooks into the Archetypes framework by registering
an ISchema adapter for BaseContent and BaseFolder, making it responsible
for providing the schema for all types derived from those classes. This
includes all standard Plone content types. Since only one ISchema adapter
can be active schemaextender provides its own mechanism to modify schemas
using named adapters. Named adapters are allowing to register more than one
schemaextender per adapted interface.

There are three types of adapters available:

* ISchemaExtender: using this adapter you can add new fields to a schema.

* IOrderableSchemaExtender: this adapters makes it possible to both add
new fields and reorder fields. This is more costly than just adding new
fields.

* IBrowserLayerAwareExtender: this adapters are making use of
plone.browserlayer, so that the extender is only available if a layer is
registered.

* ISchemaModifier: this is a low-level hook that allows direct manipulation
of the schema. This can be very dangerous and should never be used if one
does not know exactly what she/he is doing!


The adapter types are documented in the ''interfaces.py'' file in
archetypes.schemaextender.


Simple example
==============

As an example we will add a simple boolean field to the standard
Plone document type. First we need to create a field class::

from Products.Archetypes.public import BooleanField
from archetypes.schemaextender.field import ExtensionField

class MyBooleanField(ExtensionField, BooleanField):
"""A trivial field."""

schemaextender can not use the standard Archetypes fields directly
since those rely on the class generation logic generating accessors
and mutator methods. By using the ExtensionField mix-in class we can
still use them. Make sure the ExtensionField mix-in comes first, so it
properly overwrites the standard methods.

Next we have to create an adapter that will add this field::

from zope.component import adapts
from zope.interface import implements
from archetypes.schemaextender.interfaces import ISchemaExtender
from Products.Archetypes.public import BooleanWidget
from Products.ATContentTypes.interface import IATDocument

class PageExtender(object):
adapts(IATDocument)
implements(ISchemaExtender)


fields = [
MyBooleanField("super_power",
widget = BooleanWidget(
label="This page has super powers")),
]

def __init__(self, context):
self.context = context

def getFields(self):
return self.fields

Try to store the fields on the class, that way they aren't created each
time the getFields method gets called. Generally you should make sure
getFields does as few things as possible, because it's called very often.

The final step is registering this adapter with the Zope component
architecture. Since we already declared the interface we provide and
which type of object we adapt this can be done very quickly in
configure.zcml (assuming you put the code above in a file extender.py)::

<configure xmlns="http://namespaces.zope.org/zope"
xmlns:five="http://namespaces.zope.org/five">

<include package="archetypes.schemaextender" />
<adapter factory=".extender.PageExtender" />
</configure>

Custom fields
=============

If you want you can make more complicated field types as well. The only
requirement is that you need to have ExtensionField as the first parent
class for your field type. As an example here is a field that toggles a
marker interface on an object::

from zope.interface import Interface
from zope.interface import alsoProvides
from zope.interface import noLongerProvides
from Products.Archetypes.public import BooleanField
from archetypes.schemaextender.field import ExtensionField

def addMarkerInterface(obj, *ifaces):
for iface in ifaces:
if not iface.providedBy(obj):
alsoProvides(obj, iface)


def removeMarkerInterface(obj, *ifaces):
for iface in ifaces:
if iface.providedBy(obj):
noLongerProvides(obj, iface)


class ISuperPower(Interface):
"""Marker interface for classes that can do amazing things."""


class InterfaceMarkerField(ExtensionField, BooleanField):
def get(self, instance, **kwargs):
return ISuperPower.providedBy(instance)

def getRaw(self, instance, **kwargs):
return ISuperPower.providedBy(instance)

def set(self, instance, value, **kwargs):
if value:
addMarkerInterface(instance, ISuperPower)
else:
removeMarkerInterface(instance, ISuperPower)
Changelog
=========

2.0.1 - 2010-05-23
------------------

* Disable the schema cache during test runs.
[hannosch]

2.0 - 2010-05-23
----------------

* Removed the ``caching.zcml`` and enabled caching by default. You can use
a different caching implementation by using an ``overrides.zcml`` file.
[hannosch]

* Added ``z3c.autoinclude`` entry point to mark this as a Plone plugin.
[hannosch]

1.6 - 2010-03-22
----------------

* Fix index accessor to support setting custom accessor methods.
[witsch]

1.5 - 2009-11-18
----------------

* Fixed test failure in usage.txt.
[hannosch]

* Standardized package metadata layout.
[hannosch]

1.4 - 2009-11-05
----------------

* Fix schema copying to also include properties and layers.
[maerteijn]

1.3 - 2009-10-20
----------------

* Refactored the TranslatableExtensionField getMutator to directly reuse the
generatedMutatorWrapper from LinguaPlone itself. This avoids duplicating the
logic and lets schemaextender fields use the special reference field
handling introduced in LinguaPlone. This change introduces a version
requirement for LinguaPlone of at least 3.0b6.
[hannosch]

1.2 - 2009-10-10
----------------

* Add `ISchema` adapter using simple caching on the request in order to
avoid redundant calculation of the (extended) schema. The adapter is
not enabled by default and can be activated by loading `caching.zcml`.
[witsch]

* Avoid using the overridden `+` operator when copying the original schema
as this will needlessly validate all fields again.
[witsch]

* Added missing changelog entry.
[hannosch, woutervh]

1.1 - 2009-06-03
----------------

* Added support for LinguaPlone language independent fields, by seamlessly
using a new TranslatableExtensionField when LP is installed.
[hannosch]

* Added a proper interface to the IExtensionField.
[hannosch]

* Adjusted tests for Plone 3.3.
[hannosch]

* Minor adjustment in documentation: a) don't adapt the class in the example,
b) explain why named adapters are used.
[jensens]

* Schema modifiers now also browserlayer-aware.
[jessesnyder]

1.0 - 2008-07-17
----------------

* No changes since 1.0rc1.

1.0rc1 - 2008-04-07
-------------------

* Added optional plone.browserlayer support. Extenders implementing
IBrowserLayerAwareExtender need to have a layer attribute. Those extenders
are taken into account only if the specified layer is active.
[jensens]

1.0b1 - 2007-12-07
------------------

* Schema modifiers implementing ISchemaModifier are now responsible for
copying fields they modify. See README and the doc strings.
[fschulze]

* Added a simple benchmark and made some optimizations by avoiding a lot
of field copying.
[fschulze, wiggy]

* Use a marker interface instead of overrides.zcml - this means you don't
need to muck with overrides in dependent products.
[optilude]

* Added code to allow addition of new schemata. We need an ordered
dictionary to not bork the order of the schemata.
[jensens]

* Add a small benchmark utility.
[wichert]

* Replace the high-level test with unit-tests and extend the test coverage.
[wichert]

* Rewrite the README to be more human readable.
[wichert]


1.0a1 - 2007-10-15
------------------

* First public release.