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Re: Inheritance with records in more than 1 subclass
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Re: Inheritance with records in more than 1 subclass


  • Subject: Re: Inheritance with records in more than 1 subclass
  • From: Ken Anderson <email@hidden>
  • Date: Thu, 19 May 2005 20:07:34 -0400

Omar,

In any inheritance hierarchy, you must be able to positively identify what the final entity/class a record will be. If you have someone who is both a customer and employee, they should have 2 different person records. If you have an existing database where this is not possible, then you cannot use this type of inheritance scheme.

Do you have a way in the person record to identify that they're one, the other, or both? If so, maybe you should consider having a third sub-entity, 'EmployeeCustomer'. When I have situations like this and I need methods for both, I often have the methods in a separate file that I include in both implementations (I've done this in Objective-C - not Java). It's sort of a cheating form of multiple inheritance.

In any case, good luck!

Ken

On May 19, 2005, at 7:46 PM, Omar wrote:

Hi all,

I am trying to use single table inheritance for a cetain project I have on hand but am having problems where a record can be of 2 types, for example in the Apple documentation (http:// developer.apple.com/documentation/WebObjects/UsingEOModeler/ 7ModelingInheritance/chapter_7_section_2.html) there are 3 objects, Person, Employee and Customer.

Suppose the Person is both an Employee AND a Customer, If I first fetch an Employee WO fetches everything just fine but then later I try to fetch records from Customer it tells me it can't find current_order or previous_order for example, it looks like WO is caching the record and won't refresh it since its a different class, how can I get this to work properly?


Thanks in advance,

Omar
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 >Inheritance with records in more than 1 subclass (From: Omar <email@hidden>)

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