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J2EE.EJB.container-managed-relations: Are they necessary?

Posted on 2004-07-30
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Last Modified: 2013-12-03
I'm creating several entity beans that use CMP to access a MySQL database. I've already added constraints to the tables in the database using SQL commands. However, I read that the constraining relationships between entity beans (one-to-one, one-to-many, etc.) can also be specified in the deployment descriptors (xml files). If I were to make use of these container-manged-relations, would it still be necessary to use foreign key constraints in the database? If I choose to leave all of the constraints in the database, is there a reason to specify contain-managed-relations?

Thanks.
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Question by:bobwood2000
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8 Comments
 
LVL 30

Accepted Solution

by:
Mayank S earned 2000 total points
ID: 11687592
Treat the database as a separate, independent entity. The database should be a replica of the real-world objects, so if the relationship actually exists, the database should reflect it.

Today, you're using an EJB to access it. Tomorrow, you might be accessing the DB through a .NET application or through some other application (or maybe just simple queries/ stored procedures).

The DB design and relationships should always be complete.
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Author Comment

by:bobwood2000
ID: 11719634
Thanks.
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LVL 30

Expert Comment

by:Mayank S
ID: 11723055
Welcome, but why a B :-( ? I thought I gave sufficient explanation.
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LVL 30

Expert Comment

by:Mayank S
ID: 11723057
I hope you know about the grading system at EE.
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Author Comment

by:bobwood2000
ID: 11738738
I thought Mayankeagle gave a helpful response, and since it was the only response I received, I accepted it. However, it did not fully answer the question I asked, so I thought B ("good") was more appropriate than "perfect". Upon reading about the grading system, I see that I may have misused the grading system. If so, please change the grade to an A. Thanks, and sorry for difficulty.
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LVL 30

Expert Comment

by:Mayank S
ID: 11742282
Thanks, bobwood2000. The answer I gave was short but I guess that it was concise and complete. I gave you at least 3 vital reasos why you should maintain the relationships in the database:

1. The database should be a complete replica of the real-world entities that it represents and so, the relationships must be complete.

2. The database is a separate entity, so treat it as one. Don't couple it to your J2EE application.

3. Maintaining the database relationships prefectly will help you access it from any other application, like a C# or VB or ASP .NET application too, because it is indeed a separate entity accessible from anywhere.

:-)
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