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CDO/Client
Contents
Introduction
CDOObjects represent the object instances of the models that your application deals with. Internally each such object is managed by a singleton CDOStateMachine. The state machine accurately transits objects and trees of objects through the states TRANSIENT, NEW, CLEAN, DIRTY, PROXY and CONFLICT. When a CDOObject is in one of the persistent states NEW, CLEAN or DIRTY the state machine associates a CDORevision that carries the current values of the modeled structural features. All revisions created or used in a CDOSession are shared by the CDORevisionMnager of that session. CDOObjects are only known to the CDO client. Only revisions are subject to (network) transfers between client and server.
CDOObject
Interface
A CDOObject is basically an EObject with a handful of additional read-only features as the following java code shows:
public interface CDOObject extends EObject { public CDOClass cdoClass(); public CDOID cdoID(); public CDOState cdoState(); public CDOView cdoView(); public CDOResource cdoResource(); public CDORevision cdoRevision(); }
The method names differ from the regular Java getter notation to make it less likely that name collisions with your model name space occur. To understand the details about the return types you should browse the JavaDoc.
Categories
While a user application always deals with EObjects the internal CDOStateMachine interacts with InternalCDOObjects. Depending on how the EObjects relate to the InternalCDOObjects there are a handful of different categories of CDOObjects, that is, implementations of InternalCDOObject. The following type hierarchy shows an example with the shipped test model installed:
The main categories are:
- Native objects extend CDOObjectImpl and fall into three sub categories:
- Generated native objects directly extend CDOObjectImpl and result from slightly modified GenModels
- Dynamic native objects are of class DynamicCDOObjectImpl and result from dynamic models added to a session's package registry
- Resources are of class CDOResourceImpl (which also implements CDOObject and thus EObject!)
- Legacy objects extend EObjectImpl and fall into two sub categories to interface the CDOStateMachine:
- Unwoven legacy objects interface the state machine via an EMF adapter of class CDOAdapterImpl
- Woven legacy objects interface the state machine via an AspectJ inter type declaration of class CDOCallbackImpl
- Meta objects are the EModelElements contained in a session's package registry. Although their state is immutable they interface the state machine via CDOMetaImpl instances so that they can be referenced from ordinary objects.
From a CDO perspective native objects are the most efficient and full featured ones. They are the only category that combine the user application contract and the CDO state machine contract in a single object instance. Whenever possible you should generate your models to produce subclasses of CDOObjectImpl! The following table compares some important characteristics of the different object categories:
Model Type | Native | Legacy | Meta | |||
Dynamic | Generated | Unwoven | Woven | |||
Development Artifacts |
Ecore | Unaffected | N/A | |||
Genmodel | N/A | Slightly modified | Unaffected | |||
Instance Interface | CDOObject | EObject | EModelObject | |||
Statemachine Interface | CDOAdapter | CDOCallback | CDOMeta | |||
Location of Internal Values |
class | DynamicCDOObject | Java Byte Code | |||
store | CDOObject | N/A | ||||
view | CDOAdapter | CDOCallback | CDOMeta | |||
id | CDOSession | |||||
state | N/A | |||||
revision | ||||||
resource | ||||||
Location of Model Values per CDOState |
TRANSIENT | EObject | ||||
NEW | CDORevision | EObject and CDORevision | ||||
DIRTY | ||||||
CLEAN | EModelObject |