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CMP m:n relationships: database table mapping
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Posted By:   Pizzinelli_Alberto
Posted On:   Thursday, May 16, 2002 02:16 AM

I created a system that stores the information of a Student - Course m:n relationship. The relationship at database schema level is kept by a third table called Enrollments that has in addition at the foreign keys of the other two tables some fields that stores the datetime of creation, etc...(It's a fake m:n relationship. Really I use two 1:n relationships between the three tables) I've created three entity beans StudentEJB,EnrollmentEJB,CourseEJB(matching the corresponding table fields). In the deployment descriptor I specified two 1:n relationships. One for StudentEJB-EnrollmentEJB and one for CourseEJB-EnrollmentEJB When I deployed the application I expected that in my database (it's Oracle but it doesn   More>>

I created a system that stores the information of a Student - Course m:n relationship.

The relationship at database schema level is kept by a third table called Enrollments that has in addition at the foreign keys of the other two tables some fields that stores the datetime of creation, etc...(It's a fake m:n relationship. Really I use two 1:n relationships between the three tables)



I've created three entity beans StudentEJB,EnrollmentEJB,CourseEJB(matching the corresponding table fields). In the deployment descriptor I specified two 1:n relationships. One for StudentEJB-EnrollmentEJB and one for CourseEJB-EnrollmentEJB



When I deployed the application I expected that in my database (it's Oracle but it doesn't matter) there were three tables for data (Student - Enrollment - Course), but I got the following situation:



Five tables: Student, Enrollment, Course, Student-Enrollment(the 1st 1:n
relationship), Course-Enrollment (the 2nd 1:n relationship)



(Entity Beans: StudentEJB,EnrollmentEJB,CourseEJB)



In my database the last two tables are unnecessary.



Why J2ee force the creation of another table per relationship?

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Re: CMP m:n relationships: database table mapping

Posted By:   Ankur_Lamba  
Posted On:   Saturday, May 25, 2002 11:44 PM

try this without the enrollment table(bean).
use CMR, let the application server worry about maintaining relationship.
please do tell what you got from this.

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