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Posted to ojb-user@db.apache.org by Gary <gl...@yahoo.com> on 2004/03/30 21:00:47 UTC

AbstractPersistentField Question

I am wondering why the methods getFieldRecursive() and
getNestedFieldRecursive() in class
AbstractPersistentField are private.  I would like to
have the ability to override them in a custom
persistent field implementation.

Here is my dilemma:

I have the following classes:

package ojb;

public interface IParent {
	IChild getChild();
	void setChild(IChild child);
}

package ojb;

public interface IChild {
	String getDescription();
	void setDescription(String description);
}

package ojb;

public class Parent implements IParent {
	private IChild child = null;
	
	public Parent() {
		super();
	}

	public IChild getChild() {
		return child;
	}

	public void setChild(IChild child) {
		this.child = child;
	}

}

package ojb;

public class Child implements IChild {
	private String description = null;
	
	public Child() {
		super();
	}

	public String getDescription() {
		return description;
	}

	public void setDescription(String string) {
		description = string;
	}

}



I have the following OJB metadata.
<field-descriptor
name="child::description"
      column="childDescription"
      jdbc-type="VARCHAR"
/>
  
I am using a subclass of
PersistentFieldIntrospectorImpl.  The problem is that
when it tries to resolve �child::description,� it ends
up going through the �IChild getChild()� method
signature.  This causes it to analyze the fields of
IChild; of course there aren�t any, so it fails with a
MetadataException.

If I could override methods getFieldRecursive() and
getNestedFieldRecursive(), I could substitute at run
time a class that implements IChild.

Any ideas?  I really need to return a reference to an
interface here, rather than to a concrete class, as
our design is heavily interface based.

Thanks again, Gary


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Re: AbstractPersistentField Question

Posted by Thomas Dudziak <to...@first.gmd.de>.
I've tried your classes and descriptor, and I've found one problem which
is concerned with the initialization of the nested field. To be more
precise, when reading an object from the database, OJB must create the
nested field (child in your case, e.g. setChild/getChild when using
IProduct). In order to do so, it creates an instance (line 293 in
AbstractPersistentField) using newInstance(). This of course won't work
with IChild. I've extracted the newInstance line into a new protected
method createNestedFieldValue which you could override in your
PersistentField subtype like this:

public class MyPersistentFieldImpl extends PersistentFieldIntrospectorImpl
{
    public MyPersistentFieldImpl()
    {
        super();
    }

    public MyPersistentFieldImpl(Class aClass, String aPropertyName)
    {
        super(aClass, aPropertyName);
    }

    protected Object createNestedFieldValue(PersistentField
nestedField) throws InstantiationException, IllegalAccessException
	{
        Class type = nestedField.getType();

        // this of course should be more generic
        if (type == IChild.class)
        {
        	return new Child();
        }
        else
        {
        	return super.createNestedFieldValue(nestedField);
        }
    }
}

Tom


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Re: AbstractPersistentField Question

Posted by Gary <gl...@yahoo.com>.
Thomas:

Thanks for your reply.

I am already at version 1.17 of
AbstractPersistentField .

I have already tried overriding computeField(), and in
it calling AbstractPersistentField.computeField(); I
catch the MetadateException and then try to replace
the interface Class with an actual implementer Class. 
The problem is that the interface Class I need to
replace is not the one I pass in to computeField(),
but the one that is the next level down (in the
recursion chain).  This is done in the private
methods, and so I have no way to modify that behavior.

Am I explaining this in such a way as to make the
problem clear?  If methods getFieldRecursive() and
getNestedFieldRecursive() were protected, I could
modify them and substitute my implementer Class for
the interface Class when needed...

The actual exception thrown is originally a
NoSuchFieldException thrown from getFieldRecursive().

Gary

--- Thomas Dudziak <to...@first.gmd.de> wrote:
> On Tue, 30 Mar 2004, Gary wrote:
> 
> > I am wondering why the methods getFieldRecursive()
> and
> > getNestedFieldRecursive() in class
> > AbstractPersistentField are private.  I would like
> to
> > have the ability to override them in a custom
> > persistent field implementation.
> > 
> > Here is my dilemma:
> > 
> > I have the following classes:
> > 
> > package ojb;
> > 
> > public interface IParent {
> > 	IChild getChild();
> > 	void setChild(IChild child);
> > }
> > 
> > package ojb;
> > 
> > public interface IChild {
> > 	String getDescription();
> > 	void setDescription(String description);
> > }
> > 
> > package ojb;
> > 
> > public class Parent implements IParent {
> > 	private IChild child = null;
> > 	
> > 	public Parent() {
> > 		super();
> > 	}
> > 
> > 	public IChild getChild() {
> > 		return child;
> > 	}
> > 
> > 	public void setChild(IChild child) {
> > 		this.child = child;
> > 	}
> > 
> > }
> > 
> > package ojb;
> > 
> > public class Child implements IChild {
> > 	private String description = null;
> > 	
> > 	public Child() {
> > 		super();
> > 	}
> > 
> > 	public String getDescription() {
> > 		return description;
> > 	}
> > 
> > 	public void setDescription(String string) {
> > 		description = string;
> > 	}
> > 
> > }
> > 
> > 
> > 
> > I have the following OJB metadata.
> > <field-descriptor
> > name="child::description"
> >       column="childDescription"
> >       jdbc-type="VARCHAR"
> > />
> >   
> > I am using a subclass of
> > PersistentFieldIntrospectorImpl.  The problem is
> that
> > when it tries to resolve �child::description,� it
> ends
> > up going through the �IChild getChild()� method
> > signature.  This causes it to analyze the fields
> of
> > IChild; of course there aren�t any, so it fails
> with a
> > MetadataException.
> > 
> > If I could override methods getFieldRecursive()
> and
> > getNestedFieldRecursive(), I could substitute at
> run
> > time a class that implements IChild.
> > 
> > Any ideas?  I really need to return a reference to
> an
> > interface here, rather than to a concrete class,
> as
> > our design is heavily interface based.
> 
> Have you tried the CVS version ? I made some changed
> that may be of
> interest to you:
> 
> * methods getFieldRecursive and
> getNestedRecursiveField are static and,
> though still private, you can use them via the
> protected static method
> computeField in AbstractPersistentField
> 
> * I fixed getFieldRecursive such that it no longer
> throws an exception
> when given an interface
> 
> * support for interfaces in the repository
> descriptor is now much
> better; specifically using
> PersistentFieldIntrospectorImpl
> (bean-access) or PersistentFieldAutoProxyImpl
> (detects access method
> automatically - best for mixing concrete classes and
> interfaces) should
> work much better now
> 
> Perhaps you could try the CVS version with the
> unmodified
> PersistentFieldIntrospectorImpl, and if you still
> have problems, then
> please post the stacktrace ?
> 
> Tom
> 
> 
>
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Re: AbstractPersistentField Question

Posted by Thomas Dudziak <to...@first.gmd.de>.
On Tue, 30 Mar 2004, Gary wrote:

> I am wondering why the methods getFieldRecursive() and
> getNestedFieldRecursive() in class
> AbstractPersistentField are private.  I would like to
> have the ability to override them in a custom
> persistent field implementation.
> 
> Here is my dilemma:
> 
> I have the following classes:
> 
> package ojb;
> 
> public interface IParent {
> 	IChild getChild();
> 	void setChild(IChild child);
> }
> 
> package ojb;
> 
> public interface IChild {
> 	String getDescription();
> 	void setDescription(String description);
> }
> 
> package ojb;
> 
> public class Parent implements IParent {
> 	private IChild child = null;
> 	
> 	public Parent() {
> 		super();
> 	}
> 
> 	public IChild getChild() {
> 		return child;
> 	}
> 
> 	public void setChild(IChild child) {
> 		this.child = child;
> 	}
> 
> }
> 
> package ojb;
> 
> public class Child implements IChild {
> 	private String description = null;
> 	
> 	public Child() {
> 		super();
> 	}
> 
> 	public String getDescription() {
> 		return description;
> 	}
> 
> 	public void setDescription(String string) {
> 		description = string;
> 	}
> 
> }
> 
> 
> 
> I have the following OJB metadata.
> <field-descriptor
> name="child::description"
>       column="childDescription"
>       jdbc-type="VARCHAR"
> />
>   
> I am using a subclass of
> PersistentFieldIntrospectorImpl.  The problem is that
> when it tries to resolve �child::description,� it ends
> up going through the �IChild getChild()� method
> signature.  This causes it to analyze the fields of
> IChild; of course there aren�t any, so it fails with a
> MetadataException.
> 
> If I could override methods getFieldRecursive() and
> getNestedFieldRecursive(), I could substitute at run
> time a class that implements IChild.
> 
> Any ideas?  I really need to return a reference to an
> interface here, rather than to a concrete class, as
> our design is heavily interface based.

Have you tried the CVS version ? I made some changed that may be of
interest to you:

* methods getFieldRecursive and getNestedRecursiveField are static and,
though still private, you can use them via the protected static method
computeField in AbstractPersistentField

* I fixed getFieldRecursive such that it no longer throws an exception
when given an interface

* support for interfaces in the repository descriptor is now much
better; specifically using PersistentFieldIntrospectorImpl
(bean-access) or PersistentFieldAutoProxyImpl (detects access method
automatically - best for mixing concrete classes and interfaces) should
work much better now

Perhaps you could try the CVS version with the unmodified
PersistentFieldIntrospectorImpl, and if you still have problems, then
please post the stacktrace ?

Tom


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