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From "Matthew Adams" <matthew.ad...@xcalia.com>
Subject JDOHelper.isLoaded proposal
Date Sat, 14 Apr 2007 00:52:25 GMT
Hi everyone,
 
After discussion on today's call, I'm putting forth a proposal to add a
method to JDOHelper that allows users to determine whether or not a
given object's field is loaded.  There are two options to handle
implementations that can't support loaded field checking, especially
when detached (essentially binary compatible v. non-binary compatible
implementations).  Option A adopts an approach that uses Boolean objects
instead of primitives, leaving null as a return value for
implementations that won't/can't support it.  Option B takes an
exception-based approach and uses boolean primitives.  I'm not sure
which I prefer; let's discuss.

This has been filed in JIRA as JDO-483.
 
<proposal option="A">
 
JDOHelper
 
Checking whether fields are loaded
 
In some use cases, an application may need to know whether or not a
given field is loaded, for example when marshaling data from detached
objects to data transfer objects (DTOs).
 
Transient fields
 
Transient fields are always considered loaded.
 
Implementation support
 
Some implementations may not be able to support the ability to check the
loaded status of a field, especially when the object is detached.  If
the implementation does not support checking whether a field is loaded,
then it must return null from the isLoaded methods.
 
Boolean isLoaded(String fieldName, Object pc);
 
If the field in the most-derived class of the given object's class
identified by the given name is loaded in the given object, Boolean.TRUE
is returned.  If the field is not loaded, Boolean.FALSE is returned.  If
the given field name is not declared by the given object's class or its
direct or indirect superclasses, then JDOUserException is thrown.  If
the implementation does not support checking the loaded state of a
field, null is returned.  This method is equivalent to calling
isLoaded(fieldName, pc, pc.getClass());
 
Boolean isLoaded(String fieldName, Object pc, Class c);
 
This method exists to support the case where a class hides fields
defined in a superclass and an application wants to determine the loaded
state of the field in the superclass.  In most cases, the given Class,
c, will be identical to the class of the given object, pc (that is, c ==
pc.getClass() will return true).  If the class of the given object, pc,
is a subclass of the given Class, c, then the loaded state of the field
defined on c is given.  If the given Class c is not identical to the
class of or a superclass of the given object, pc, then JDOUserException
is thrown.  If the given Class represents an interface, then
JDOUserException is thrown.
 
If the field of the given class is loaded, Boolean.TRUE is returned.  If
the field is not loaded, Boolean.FALSE is returned.  If the
implementation does not supporting checking the loaded state of a field,
null is returned.
 
</proposal>
 
<proposal option="B">
 
JDOHelper
 
Checking whether fields are loaded
 
In some use cases, an application may need to know whether or not a
given field is loaded, for example, when marshaling data from detached
objects to data transfer objects (DTOs).
 
Transient fields
 
Transient fields are always considered loaded.
 
Implementation support
 
Some implementations may not be able to support the ability to check the
loaded status of a field, especially when the object is detached.  If
the implementation does not support checking whether a field is loaded,
then it must throw JDOUnsupportedOperationException from the isLoaded
methods.
 
boolean isLoaded(String fieldName, Object pc);
 
If the field in the most-derived class of the given object's class
identified by the given name is loaded in the given object, true is
returned, otherwise false is returned.  If the given field name is not
defined by the given object's class or its direct or indirect
superclasses, then a JDOUserException is thrown.  If the implementation
does not support checking the loaded state of a field,
JDOUnsupportedOptionException is thrown.  This method is equivalent to
calling isLoaded(fieldName, pc, pc.getClass());
 
boolean isLoaded(String fieldName, Object pc, Class c);
 
This method exists to support the case where a class hides fields
defined in a superclass and an application wants to determine the loaded
state of the field in the superclass.  In most cases, the given Class,
c, will be identical to the class of the given object, pc.  If the class
of the given object, pc, is a subclass of the given Class, c, then the
loaded state of the field defined on c is given.  If the given Class c
is not identical to the class and is not a superclass of the given
object, pc, then a JDOUserException is thrown.  If the given Class
represents an interface, then JDOUserException is thrown.
 
If the field of the given class is loaded, true is returned, otherwise
false is returned.  If the implementation does not support checking the
loaded state of a field, JDOUnsupportedOptionException is thrown.
 
</proposal>
 
Matthew T. Adams
Senior Consultant & Product Marketing Director
Xcalia, Inc.
matthew.adams@xcalia.com
+1 206 331 3833 Office
+1 253 732 1051 Mobile
+1 815 331 0952 Fax
http://www.xcalia.com <http://www.xcalia.com/> 
745 Emerson St.
Palo Alto, CA  94301
 
Xcalia provides dynamic integration software for agile enterprises to
easily create transactional composite applications. Our unique
intermediation approach enables unified, real-time access to
heterogenous data and services. Intermediation is adaptive and
configurable so application changes can be made quickly and cost
effectively without impacting the underlying systems or infrastructure.

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