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+.. _zca:
+
+Managing ZCA with PyAMS
+=======================
+
+The **Zope Component Architecture** (aka ZCA) is used by the Pyramid framework "under the hood" to handle interfaces,
+adapters and utilities. You don't **have to** use it in your own applications. But you can.
+
+The ZCA is mainly adding elements like **interfaces**, **adapters** and **utilities** to the Python language. It
+allows you to write a framework or an application by using **components** which can be extended easily.
+
+You will find several useful resources about ZCA concepts on the internet.
+
+
+Local utilities
+---------------
+
+In ZCA, a **utility** is a **registered** component which provides an **interface**. This interface is the
+**contract** which defines features (list of attributes and methods) provided by the component which implements it.
+
+When a Pyramid application starts, a **global registry** is created to register a whole set of utilities and
+adapters; this registration can be done via ZCML directives or via native Python code.
+In addition, PyAMS allows you to define **local utilities**, which are stored and registered in the ZODB via a **site
+manager**.
+
+
+Defining site root
+------------------
+
+One of PyAMS pre-requisites is to use the ZODB, at least to store the site root application, it's configuration and a
+set of local utilities. :ref:`site` describes application startup and **local site manager** initialization process.
+
+This site can be used to store **local utilities** whose configuration, which is easily available to site
+administrators through management interface, is stored in the ZODB.
+
+
+Registering global utilities
+----------------------------
+
+**Global utilities** are components providing an interface which are registered in the global registry.
+PyAMS_utils package provides custom annotations to register global utilities without using ZCML. For example, a skin
+is nothing more than a simple utility providing the *ISkin* interface:
+
+.. code-block:: python
+
+ from pyams_default_theme.layer import IPyAMSDefaultLayer
+ from pyams_skin.interfaces import ISkin
+ from pyams_utils.registry import utility_config
+
+ @utility_config(name='PyAMS default skin', provides=ISkin)
+ class PyAMSDefaultSkin(object):
+ """PyAMS default skin"""
+
+ label = _("PyAMS default skin")
+ layer = IPyAMSDefaultLayer
+
+This annotation registers a utility, named *PyAMS default skin*, providing the *ISkin* interface. It's the developer
+responsibility to provide all attributes and methods required by the provided interface.
+
+
+Registering local utilities
+---------------------------
+
+A local utility is a persistent object, registered in a *local site manager*, and providing a specific interface (if
+a component provides several interfaces, it can be registered several times).
+
+Some components can be required by a given package, and created automatically via the *pyams_upgrade* command line
+script; this process relies on the *ISiteGenerations* interface, for example for the timezone utility, a component
+provided by PyAMS_utils package to handle server timezone and display times correctly:
+
+.. code-block:: python
+
+ from pyams_utils.interfaces.site import ISiteGenerations
+ from pyams_utils.interfaces.timezone import IServerTimezone
+
+ from persistent import Persistent
+ from pyams_utils.registry import utility_config
+ from pyams_utils.site import check_required_utilities
+ from pyramid.events import subscriber
+ from zope.container.contained import Contained
+ from zope.interface import implementer
+ from zope.schema.fieldproperty import FieldProperty
+
+ @implementer(IServerTimezone)
+ class ServerTimezoneUtility(Persistent, Contained):
+
+ timezone = FieldProperty(IServerTimezone['timezone'])
+
+ REQUIRED_UTILITIES = ((IServerTimezone, '', ServerTimezoneUtility, 'Server timezone'),)
+
+ @subscriber(INewLocalSite)
+ def handle_new_local_site(event):
+ """Create a new ServerTimezoneUtility when a site is created"""
+ site = event.manager.__parent__
+ check_required_utilities(site, REQUIRED_UTILITIES)
+
+ @utility_config(name='PyAMS timezone', provides=ISiteGenerations)
+ class TimezoneGenerationsChecker(object):
+ """Timezone generations checker"""
+
+ generation = 1
+
+ def evolve(self, site, current=None):
+ """Check for required utilities"""
+ check_required_utilities(site, REQUIRED_UTILITIES)
+
+Some utilities can also be created manually by an administrator through the management interface, and registered
+automatically after their creation. For example, this is how a ZEO connection utility (which is managing settings to
+define a ZEO connection) is registered:
+
+.. code-block:: python
+
+ from pyams_utils.interfaces.site import IOptionalUtility
+ from pyams_utils.interfaces.zeo import IZEOConnection
+ from zope.annotation.interfaces import IAttributeAnnotatable
+ from zope.lifecycleevent.interfaces import IObjectAddedEvent, IObjectRemovedEvent
+
+ from persistent import Persistent
+ from pyramid.events import subscriber
+ from zope.container.contained import Contained
+
+ @implementer(IZEOConnection)
+ class ZEOConnection(object):
+ """ZEO connection object. See source code to get full implementation..."""
+
+ @implementer(IOptionalUtility, IAttributeAnnotatable)
+ class ZEOConnectionUtility(ZEOConnection, Persistent, Contained):
+ """Persistent ZEO connection utility"""
+
+ @subscriber(IObjectAddedEvent, context_selector=IZEOConnection)
+ def handle_added_connection(event):
+ """Register new ZEO connection when added"""
+ manager = event.newParent
+ manager.registerUtility(event.object, IZEOConnection, name=event.object.name)
+
+ @subscriber(IObjectRemovedEvent, context_selector=IZEOConnection)
+ def handle_removed_connection(event):
+ """Un-register ZEO connection when deleted"""
+ manager = event.oldParent
+ manager.unregisterUtility(event.object, IZEOConnection, name=event.object.name)
+
+*context_selector* is a custom subscriber predicate, so that subscriber event is activated only if object concerned
+by an event is providing given interface.
+
+
+Looking for utilities
+---------------------
+
+ZCA provides the *getUtility* and *queryUtility* functions to look for a utility. But these methods only applies to
+global registry.
+
+PyAMS package provides equivalent functions, which are looking for components into local registry before looking into
+the global one. For example:
+
+.. code-block:: python
+
+ from pyams_security.interfaces import ISecurityManager
+ from pyams_utils.registry import query_utility
+
+ manager = query_utility(ISecurityManager)
+ if manager is not None:
+ print("Manager is there!")
+
+All ZCA utility functions have been ported to use local registry: *registered_utilities*, *query_utility*,
+*get_utility*, *get_utilities_for*, *get_all_utilities_registered_for* functions all follow the equivalent ZCA
+functions API, but are looking for utilities in the local registry before looking in the global registry.
+
+
+Registering adapters
+--------------------
+
+An adapter is also a kind of utility. But instead of *just* providing an interface, it adapts an input object,
+providing a given interface, to provide another interface. An adapter can also be named, so that you can choose which
+adapter to use at a given time.
+
+PyAMS_utils provide another annotation, to help registering adapters without using ZCML files. An adapter can be a
+function which directly returns an object providing the requested interface, or an object which provides the interface.
+
+The first example is an adapter which adapts any persistent object to get it's associated transaction manager:
+
+.. code-block:: python
+
+ from persistent.interfaces import IPersistent
+ from transaction.interfaces import ITransactionManager
+ from ZODB.interfaces import IConnection
+
+ from pyams_utils.adapter import adapter_config
+
+ @adapter_config(context=IPersistent, provides=ITransactionManager)
+ def get_transaction_manager(obj):
+ conn = IConnection(obj)
+ try:
+ return conn.transaction_manager
+ except AttributeError:
+ return conn._txn_mgr
+
+This is another adapter which adapts any contained object to the *IPathElements* interface; this interface can be
+used to build index that you can use to find objects based on a parent object:
+
+.. code-block:: python
+
+ from pyams_utils.interfaces.traversing import IPathElements
+ from zope.intid.interfaces import IIntIds
+ from zope.location.interfaces import IContained
+
+ from pyams_utils.adapter import ContextAdapter
+ from pyams_utils.registry import query_utility
+ from pyramid.location import lineage
+
+ @adapter_config(context=IContained, provides=IPathElements)
+ class PathElementsAdapter(ContextAdapter):
+ """Contained object path elements adapter"""
+
+ @property
+ def parents(self):
+ intids = query_utility(IIntIds)
+ if intids is None:
+ return []
+ return [intids.register(parent) for parent in lineage(self.context)]
+
+An adapter can also be a multi-adapter, when several input objects are requested to provide a given interface. For
+example, many adapters require a context and a request, eventually a view, to provide another feature. This is how,
+for example, we define a custom *name* column in a security manager table displaying a list of plug-ins:
+
+.. code-block:: python
+
+ from pyams_zmi.layer import IAdminLayer
+ from z3c.table.interfaces import IColumn
+
+ from pyams_skin.table import I18nColumn
+ from z3c.table.column import GetAttrColumn
+
+ @adapter_config(name='name', context=(Interface, IAdminLayer, SecurityManagerPluginsTable), provides=IColumn)
+ class SecurityManagerPluginsNameColumn(I18nColumn, GetAttrColumn):
+ """Security manager plugins name column"""
+
+ _header = _("Name")
+ attrName = 'title'
+ weight = 10
+
+As you can see, adapted objects can be given as interfaces and/or as classes.
+
+
+Registering vocabularies
+------------------------
+
+A **vocabulary** is a custom factory which can be used as source for several field types, like *choices* or *lists*.
+Vocabularies have to be registered in a custom registry, so PyAMS_utils provide another annotation to register them.
+This example is based on the *Timezone* component which allows you to select a timezone between a list of references:
+
+.. code-block:: python
+
+ import pytz
+ from pyams_utils.vocabulary import vocabulary_config
+ from zope.schema.vocabulary import SimpleTerm, SimpleVocabulary
+
+ @vocabulary_config(name='PyAMS timezones')
+ class TimezonesVocabulary(SimpleVocabulary):
+ """Timezones vocabulary"""
+
+ def __init__(self, *args, **kw):
+ terms = [SimpleTerm(t, t, t) for t in pytz.all_timezones]
+ super(TimezonesVocabulary, self).__init__(terms)