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Re: Inheritance Problem
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Re: Inheritance Problem


  • Subject: Re: Inheritance Problem
  • From: Chuck Hill <email@hidden>
  • Date: Tue, 16 May 2006 11:46:27 -0700

Hi David,

I am not too clear on our inheritance configuration from your message. Two possibilities jump to mind.

1. If you have the sub-entities in their own tables, then you can't enforce foreign-key constraints. i.e. If you have a Person entity in a Person table and an Employee entity in a Employee table, then you can't enforce a foreign-key constraint from Department to Person as the rows will actually be in the Employee table. The solution to this is to remove the impossible foreign-key constraints.

2. EOF often performs operations on the database in an order other than what you might desire. For example, it may insert a row into the Employee table before inserting the corresponding row into the Department table (assuming you are creating a new Department and Employee in the same transaction). There are two solutions to this.

If you are using a real database (e.g. whOracle, FrontBase, PostgreSQL) then generate the foreign-key constraints with DEFERRABLE INITIALLY DEFERRED. This will cause the database to check integrity when the COMMIT is issued instead of checking it after every statement is executed. With the proper EOModeler plugin (which is different than the EOF plugin), this SQL should be generated automatically.

If you are using MySQLToy or something else that does not support DEFERRABLE INITIALLY DEFERRED, there is a delegate of EOAdaptorChannel that you can use to order the operations in code. Project Wonder has an implementation of this. I have never used it, so have no more information on it.


Chuck


On May 16, 2006, at 8:25 AM, David Avendasora wrote:

Hi all,

I am trying to save an instance of a subclass to the database after creating it from scratch. I am getting a foreign-key constraint error from the database because it hasn't created the database record for the parent class yet, which has a one-to-one relationship configured in the database.

I've recreated the relationship in the DB and in EOModeler just to make sure I had done it correctly, but I'm still getting the same error.

Any ideas? Am I missing something obvious?

Thanks,

Dave
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