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From "Matthew T. Adams (JIRA)" <j...@apache.org>
Subject [jira] Created: (JDO-483) Add JDOHelper.isLoaded methods
Date Sat, 14 Apr 2007 00:53:15 GMT
Add JDOHelper.isLoaded methods
------------------------------

                 Key: JDO-483
                 URL: https://issues.apache.org/jira/browse/JDO-483
             Project: JDO
          Issue Type: Improvement
          Components: api2, api2-legacy
    Affects Versions: JDO 2 maintenance release 1
            Reporter: Matthew T. Adams


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 won't/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.
 
<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>


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