Re: [dali-dev] IPersitentType.attributes() - wildcard parameterized type

[Karen Moore <karen.moore@xxxxxxxxxx>]

Hi Tom,

Funny you should ask, I just struggled with this very recently.  In our 
model JavaPersistentType and XmlPersistentType both implement 
IPersistentType.  They each have collections of more specific attributes 
JavaPersistentAttribute and XmlPersistentAttribute.  The reason I 
changed the interface to have a wildcard-parameterized type was so that 
I could use a CloneIterator (our own utility class) in 
JavaPersistentType.attributes() to prevent concurrent modification 
problems we were having.  I did not change allAttributes() because those 
iterators could contain xml and java PersistentAttributes due to 
inheritance hierarchies that could possibly span both java and orm.xml.  
I don't know that it is possible to use the wildcard-parameterized type 
in those situations. 

I agree this solution is not the best, we have compiler warnings in 
JavaPersistentType that we haven't yet fixed. Given that background and 
the fact that I am fairly new to generics, do you have any suggestions?

The method you are writing looks very similar to some of our interface 
methods. You might want to take a look at IEntity.primaryKeyColumnName() 
and IEntity.primaryKeyAttributeName(). 

thanks,
Karen

Tom Mutdosch wrote:

> Hi there,
>
> I was just wondering why the IPersitentType.attributes() method has a 
> return type of:  Iterator<? extends IPersistentAttribute>
>
> (whereas the other methods that return Iterators have types of 
> Iterator<IPersistentAttribute>).
>
> Is the wildcard-parameterized type needed in this case?  It's not a 
> problem; it just makes the usage of it seem somewhat unwieldy:
>
> public static String getPrimaryKey(IPersistentType entity) {
>     for ( Iterator<? extends IPersistentAttribute> iter = 
> entity.attributes(); iter.hasNext(); ) {
>         IPersistentAttribute jpAtt = iter.next();
>         String attributeType = jpAtt.mappingKey();
>         // ... etc etc
>
>
>
> Thanks
> Tom
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