Hi ,
I had implemeted this similar to what tom had suggested.
Only thing is I was using factory class which will return the correct class
(one
of the sub-classes ) depending upon the tag value ; This allows to add more
sub-classes without making any change in the parent class .
Regards,
Amit
On Tue, 8 Aug 2000 14:14:41 GMT, Tom Lepski <[EMAIL PROTECTED]> wrote:
>Hi Kurt,
>I understand your Collection analogy but I think this is really a legitmate
>demand. For eg. in a system there could be Persons, Managers and Techleads.
>Now, it is quite reasonable to retrieve all the Persons in one go and then
>depending on the person perform activities. So there have to be different
>entities because operations like manage() cannot be provided in Person
>bean.
>
>But as I write this, I got another idea.
>Support all the methods in Person (actually have just one kind of entity
>bean which has superset of all the attributes) and also have a tag field
>telling whether it is a Person or Manager etc. Now depending on this tag,
>call the appropriate methods. If you call manage() on a bean that has the
>tag value of Person, throw some runtime exception!
>
>Please give your comments on this. I am sure many of the projects involving
>EJBs must have ran into this kind of situation.
>
>Please help,
>-Tom.
>
>
>>From: "Christensen, Kurt" <[EMAIL PROTECTED]>
>>Reply-To: A mailing list for Enterprise JavaBeans development
>><[EMAIL PROTECTED]>
>>To: [EMAIL PROTECTED]
>>Subject: Re: A design question...
>>Date: Mon, 7 Aug 2000 21:30:40 -0500
>>
>>Oops! I just realized that I didn't actually answer your question. What
>>you're looking for is actually sort of tricky. "findXXX" is (sort of)
>>analogous to "get(Object o)" in the Collection interface. Now, if I had:
>>
>>public class MyCollection implements Collection
>>{
>> // ...
>>}
>>
>>and
>>
>>public class MySuperCoolCollection extends MyCollection
>>{
>> // ...
>>}
>>
>>...you wouldn't expect a get() on a MyCollection to return everything in
>>MySuperCoolCollection as well. But this is what you're asking for when you
>>ask for a generic findXXX() method in the base class. Luckily, since
>>EJBHome
>>objects are basically singleton objects, we can probably accomplish
>>something along the lines of what you're looking for....
>>
>>
>>public class CarProxy
>>{
>> private EJBHome _myEJBHome;
>> private Method _myFinderMethod;
>> private static Hashtable _myChildFindByNames = new Hashtable(89);
>>
>> public CarProxy()
>> {
>> this( "CarHome" );
>> }
>>
>> public CarProxy( String jndiHomeName )
>> {
>> // Get JNDI context (app-server specific code here)
>> Context context = new InitialContext();
>>
>> // Get EJBHome object
>> Object o = context.lookup( "CarHome" );
>>
>> // Perform CORBA narrowing voodoo
>> _myEJBHome = (EJBHome)PortableRemoteObject.narrow( o,
>>EJBHome.class
>>);
>>
>> // Get the metadata for this EJB (we need to do all this
>> // because EJBHome doesn't define findByPrimaryKey() )
>> EJBMetaData ejbMetaData = ejbHome.getEJBMetaData();
>>
>> // Get the Home class for the EJB from the metadata
>> Class ejbHomeClass = ejbMetaData.getHomeInterfaceClass();
>>
>> // Get the findByName method
>> Class[] argTypes = { String.class };
>> _myFinderMethod = ejbHomeClass.getMethod( "findByName", argTypes
>>);
>>
>> // Save the finder method in our collection of finder methods
>> _myChildFindByNames.put( _myEJBHome, _myFinderMethod );
>> }
>>
>> public Car findByPrimaryKey( CarPK carPK )
>> {
>> Object[] args = { carPK };
>> return _myFinderMethod.invoke( _myEJBHome, args );
>> }
>>
>> public Collection findByName( String name )
>> {
>> ArrayList resultSet = new ArrayList();
>>
>> Enumeration keys = _myChildFindByNames.keys();
>> while( keys.hasMoreElements() )
>> {
>> EJBHome ejbHome = (EJBHome)keys.nextElement();
>> Method finderMethod = (Method)_myChildFindByNames.get(
>>ejbHome
>>);
>> Collection results = (Collection)finderMethod.invoke(
>>ejbHome,
>>name );
>> resultSet.addAll( results );
>> }
>>
>> return resultSet;
>> }
>>}
>>
>>public class SportsCarProxy
>>{
>> public SportsCarProxy()
>> {
>> super( "SportsCarHome" );
>> }
>>}
>>
>>
>>This probably isn't exactly right, but I think it's a good avenue for what
>>you're trying to accomplish. If anyone out there has any bright ideas of
>>what to do here, join in the fun...
>>
>>KurtC
>>
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>>
>
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