--On Thursday, May 11, 2000 6:34 PM -0700 Phan Anh Tran <[EMAIL PROTECTED]>
wrote:
> As you can see, it would be highly inappropriate to implement a
> PersonEntity and a LegEntity to wrap Person and Leg respectively. It
> makes more sense to have one PersonEntity bean with a reference to Person
> which in turn has a reference to Leg.
I don't see this...
In ths case, it would be very reasonable to have a person entity that had
two references, one to a left leg entity and another to a right leg entity.
If we had some kind of alian that had an unknown number of legs, it would
be reasonable for a person entity to have a Collection of leg entities. I
don't see why a PersonEntity should have a Person that in turn has a
reference to a leg.
If you need to find all the people with legs of a particular length, then
give each LegEntity a reference to their corresponding PersonEntity. Put a
finder method in the leg that returns a person entity.
Jim
>> Workaround:
>> use EntityBeans for everything. Then they will be searchable. Perhaps
>> not the most "clean" or "OO", but works.
>>
>> Once EJB 2.0 defines how to do this, we will implement this.
>>
>> /Rickard
>
> Is EJB 2.0 going to define how to map a certain class or how to specify
> custom finder methods or both? I am not at all familiar with what is
> going to be in EJB2.0. However, consider this:
>
> public class Person
> {
> private Leg leftLeg;
> private Leg rightLeg;
> }
>
> public class Leg
> {
> private byte length;
> }
>
> [Person]<>----(2)->[Leg]
>
> As you can see, it would be highly inappropriate to implement a
> PersonEntity and a LegEntity to wrap Person and Leg respectively. It
> makes more sense to have one PersonEntity bean with a reference to Person
> which in turn has a reference to Leg.
>
> However, the business logic may require the need to find all people with
> legs of a certain length. In order to support the described query
> efficiently, one would need to map Person to a Table Person and
> rightLeg/leftLeg to a Table Leg.
>
> If one did not map rightLeg and leftLeg to a separate table, one would be
> forced to load all PersonEntity bean one at a time and check their legs -
> a much more inefficient approach than a straight database level sql join.
>
> On the other hand, if there never is a nee to find all people with legs of
> certain length, the bean deployer could choose to stuff the
> rightLeg/leftLeg stuff in one column in the Table Person.
>
> I just want to make sure that EJB2.0 is going to deal with the above O->R
> mapping issues.
>
> Anh
>
>
>
>
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