Manipulating content objects

Note

Here the low level api is shown. When writing Plone Add-Ons consider using plone.api, because it covers several standard cases and is a simple, future proof and stable api.

Common APIs used to manipulate Dexterity content objects

In this section, we will describe some of the more commonly used APIs that can be used to inspect and manipulate Dexterity content objects. In most cases, the content object is referred to as context, its parent folder is referred to as folder, and the type name is example.type. Relevant imports are shown with each code snippet, though of course you are more likely to place those at the top of the relevant code module.

Content object creation and folder manipulation

This section describes means to create objects and manipulate folders.

Creating a content object

The simplest way to create a content item is via its factory:

from zope.component import createObject
context = createObject('example.type')

At this point, the object is not acquisition wrapped. You can wrap it explicitly by calling:

wrapped = context.__of__(folder)

However, it’s normally better to add the item to a folder and then re-get it from the folder.

Note that the factory is normally installed as a local utility, so the createObject() call will only work once you’ve traversed over the Plone site root.

There is a convenience method that can be used to create a Dexterity object. It is mostly useful in tests:

from plone.dexterity.utils import createContent
context = createContent('example.type', title=u"Foo")

Any keyword arguments are used to set properties on the new instance (via setattr() on the newly created object). This method relies on being able to look up the FTI as a local utility, so again you must be inside the site for it to work.

Adding an object to a container

Once an object has been created, it can be added to a container. If the container is a Dexterity container, or another container that supports a dict API (e.g. a Large Plone Folder in Plone 3 or a container based on plone.folder), you can do:

folder['some_id'] = context

You should normally make sure that the id property of the object is the same as the id used in the container.

If the object only supports the basic OFS API (as is the case with standard Plone Folders in Plone 3), you can use the _setObject() method:

folder._setObject('some_id') = context

Note that both of these approaches bypass any type checks, i.e. you can add items to containers that would not normally allow this type of content. Dexterity comes with a convenience function, useful in tests, to simulate the checks performed when content is added through the web:

from plone.dexterity.utils import addContentToContainer
addContentToContainer(folder, context)

This will also invoke a name chooser and set the object’s id accordingly, so things like the title-to-id behavior should work. As before, this relies on local components, so you must have traversed into a Plone site (PloneTestCase takes care of this for you).

To bypass folder constraints, you can use this function and pass checkConstraints=False.

You can also both create and add an object in one call:

from plone.dexterity.utils import createContentInContainer
createContentInContainer(folder, 'example.type', title=u"Foo")

Again, you can pass checkConstraints=False to bypass folder constraints, and pass object properties as keyword arguments.

Finally, you can use the invokeFactory() API, which is similar, but more generic in that it can be used for any type of content, not just Dexterity content:

new_id = folder.invokeFactory('example.type', 'some_id')
context = folder['new_id']

This always respects add constraints, including add permissions and the current user’s roles.

Getting items from a folder

Dexterity containers and other containers based on plone.folder support a dict-like API to obtain and manipulate items in folders. For example, to obtain an (acquisition-wrapped) object by name:

context = folder['some_id']

Folders can also be iterated over, and you can all items(), keys(), values() and so on, treating the folder as a dict with string keys and content objects as values.

Dexterity containers also support the more basic OFS API. You can call objectIds() to get keys, objectValues() to get a list of content objects, objectItems() to get an items()-like dict,and hasObject(id) to check if an object exists in a container.

Removing items from a folder

Again, Dexterity containers act like dictionaries, and so implement __delitem__:

del folder['some_id']

The OFS API uses the _delObject() function for the same purpose:

folder._delObject('some_id')

Object introspection

This section describes means of getting information about an object.

Obtaining an object’s schema interface

A content object’s schema is an interface, i.e. an object of type zope.interface.interface.InterfaceClass.

from zope.app.content import queryContentType
schema = queryContentType(context)

The schema can now be inspected. For example:

from zope.schema import getFieldsInOrder
fields = getFieldsInOrder(schema)

Finding an object’s behaviors

To find all behaviors supported by an object, use the plone.behavior API:

from plone.behavior.interfaces import IBehaviorAssignable
assignable = IBehaviorAssignable(context)
for behavior in assignable.enumerateBehaviors():
    behavior_schema = behavior.interface
    adapted = behavior_schema(context)
    ...

The objects returned are instances providing plone.behavior.interfaces.IBehavior. To get the behavior schema, use the interface property of this object. You can inspect this and use it to adapt the context if required.

Getting the FTI

To obtain a Dexterity FTI, look it up as a local utility:

from zope.component import getUtility
from plone.dexterity.interfaces import IDexterityFTI
fti = getUtility(IDexterityFTI, name='example.type')

The returned object provides plone.dexterity.interfaces.IDexterityFTI. To get the schema interface for the type from the FTI, you can do:

schema = fti.lookupSchema()

Getting the object’s parent folder

A Dexterity item in a Dexterity container should have the __parent__ property set, pointing to its containment parent:

folder = context.__parent__

Items in standard Plone folders won’t have this property set, at least not in Plone 3.x.

The more general approach relies on acquisition:

from Acquisition import aq_inner, aq_parent
folder = aq_parent(aq_inner(context))

Workflow

This section describes ways to inspect an object’s workflow state and invoke transitions.

Obtaining the workflow state of an object

To obtain an object’s workflow state, ask the*portal_workflow* tool:

from Products.CMFCore.utils import getToolByName
portal_workflow = getToolByName(context, 'portal_workflow')
review_state = portal_workflow.getInfoFor(context, 'review_state')

This assumes that the workflow state variable is called review_state, as is the case for almost all workflows.

Invoking a workflow transition

To invoke a transition:

portal_workflow.doActionFor(context, 'some_transition')

The transition must be available in the current workflow state, for the current user. Otherwise, an error will be raised.

Cataloging and indexing

This section describes ways of indexing an object in the portal_catalog tool.

Reindexing the object

Objects may need to be reindexed if they are modified in code. The best way to reindex them is actually to send an event and let Dexterity’s standard event handlers take care of this:

from zope.lifecycleevent import modified
modified(context)

In tests, it is sometimes necessary to reindex explicitly. This can be done with:

context.reindexObject()

You can also pass specific index names to reindex, if you don’t want to reindex everything:

context.reindexObject(idxs=['Title', 'sortable_title'])

This method comes from the Products.CMFCore.CMFCatalogAware.CMFCatalogAware mix-in class.

Security

This section describes ways to check and modify permissions. For more information, see the section on permissions.

Checking a permission

To check a permission by its Zope 3 name:

from zope.security import checkPermission
checkPermission('zope2.View', context)

Note: In a test, you may get an AttributeError when calling this method. To resolve this, call newInteraction() from Products.Five.security in your test setup (e.g. the afterSetUp() method).

To use the Zope 2 permission title:

from AccessControl import getSecurityManager
getSecurityManager().checkPermission('View', context)

Sometimes, normally in tests, you want to know which roles have a particular permission. To do this, use:

roles = [r['name'] for r in context.rolesOfPermission('View') if r['selected']]

Again, note that this uses the Zope 2 permission title.

Changing permissions

Normally, permissions should be set with workflow, but in tests it is often useful to manipulate security directly:

context.manage_permission('View', roles=['Manager', 'Owner'], acquire=True)

Again note that this uses the Zope 2 permission title.

Content object properties and methods

The following table shows the more important properties and methods available on Dexterity content objects. In addition, any field described in the type’s schema will be available as a property, and can be read and set using normal attribute access.

Property/method	Type	Description
__name__	unicode	The name (id) of the object in its container. This is a unicode string to be consistent with the Zope 3 IContained interface, although in reality it will only ever contain ASCII characters, since Zope 2 does not support non-ASCII URLs.
id	str	The name (id) of the object in its container. This is an ASCII string encoding of the __name__.
getId()	str	Returns the value of the id*property.*
isPrincipiaFolderish	bool/int	True (or 1) if the object is a folder. False (or 0) otherwise.
portal_type	str	The portal_type of this instance. Should match an FTI in the portal_types tool. For Dexterity types, should match a local utility providing IDexterityFTI. Note that the portal_type is a per-instance property set upon creation (by the factory), and should not be set on the class.
meta_type	str	A Zope 2 specific way to describe a class. Rarely, if ever, used in Dexterity. Do not set it on your own classes unless you know what you’re doing.
title_or_id()	str	Returns the value of the title property or, if this is not set, the id property.
absolute_url()	str	The full URL to the content object. Will take virtual hosting and the current domain into account.
getPhysicalPath()	tuple	A sequence of string path elements from the application root. Stays the same regardless of virtual hosting and domain. A common pattern is to use ‘/’.join(context.getPhysicalPath()) to get a string representing the path to the Zope application root. Note that it is not safe to construct a relative URL from the path, because it does not take virtual hosting into account.
title	unicode/str	Property representing the title of the content object. Usually part of an object’s schema or provided by the IBasic behavior. The default is an empty string.
Title()	unicode/str	Dublin Core accessor for the title property. Set the title by modifying this property. You can also use setTitle().
listCreators()	tuple	A list of user ids for object creators. The first creator is normally the owner of the content object. You can set this list using the setCreators() method.
Creator()	str	The first creator returned by the listCreators() method. Usually the owner of the content object.
Subject()	tuple	Dublin Core accessor for item keywords. You can set this list using the setSubject() method.
Description()	unicode/str	Dublin Core accessor for the description property, which is usually part of an object’s schema or provided by the IBasic behavior. You can set the description by setting the description attribute, or using the setDescription() method.
listContributors()	tuple	Dublin Core accessor for the list of object contributors. You can set this with setContributors().
Date()	str	Dublin Core accessor for the default date of the content item, in ISO format. Uses the effective date is set, falling back on the modification date.
CreationDate()	str	Dublin Core accessor for the creation date of the content item, in ISO format.
EffectiveDate()	str	Dublin Core accessor for the effective publication date of the content item, in ISO format. You can set this by passing a DateTime object to setEffectiveDate().
ExpirationDate()	str	Dublin Core accessor for the content expiration date, in ISO format. You can set this by passing a DateTime object to setExpirationDate().
ModificationDate()	str	Dublin Core accessor for the content last-modified date, in ISO format.
Language()	str	Dublin Core accessor for the content language. You can set this using setLanguage().
Rights()	str	Dublin Core accessor for content copyright information. You can set this using setRights().
created()	DateTime	Returns the Zope 2 DateTime for the object’s creation date. If not set, returns a “floor” date of January 1st, 1970.
modified()	DateTime	Returns the Zope 2 DateTime for the object’s modification date. If not set, returns a “floor” date of January 1st, 1970.
effective()	DateTime	Returns the Zope 2 DateTime for the object’s effective date. If not set, returns a “floor” date of January 1st, 1970.
expires()	DateTime	Returns the Zope 2 DateTime for the object’s expiration date. If not set, returns a “floor” date of January 1st, 1970.