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Cannot deploy the student, course and semester example in the spec

 
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Hi, I am trying to implement example 3 of @MapKeyJoinColumn in the spec:





CREATE TABLE  STUDENT (ID INTEGER AUTO_INCREMENT,   PRIMARY KEY (ID));
CREATE TABLE COURSE (ID INTEGER AUTO_INCREMENT, PRIMARY KEY (ID));
CREATE TABLE SEMESTER(ID INTEGER AUTO_INCREMENT, PRIMARY KEY(ID));
CREATE TABLE ENROLLMENTS (STUDENT INTEGER NOT NULL, SEMESTER INTEGER NOT NULL, COURSE INTEGER NOT NULL,   PRIMARY KEY (STUDENT, SEMESTER,COURSE));
ALTER TABLE ENROLLMENTS ADD CONSTRAINT STUREF FOREIGN KEY (STUDENT) REFERENCES STUDENT (ID);
ALTER TABLE ENROLLMENTS ADD CONSTRAINT SEMPREF FOREIGN KEY (SEMESTER) REFERENCES SEMESTER (ID);
ALTER TABLE ENROLLMENTS ADD CONSTRAINT COUREF FOREIGN KEY (COURSE) REFERENCES COURSE(ID);


When I deploy it, I get this error message:


cannot Deploy Courses
deploy is failing=Error occurred during deployment: Exception while deploying the app [Courses] : Exception [EclipseLink-28019] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Deployment of PersistenceUnit [StudentService] failed. Close all factories for this PersistenceUnit.
Internal Exception: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.IntegrityException
Descriptor Exceptions:
---------------------------------------------------------

Exception [EclipseLink-93] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: The table [SEMESTER] is not present in this descriptor.
Descriptor: RelationalDescriptor(com.examples.model.Course --> [DatabaseTable(COURSE)])


I am using Eclipse with Glassfish 4.1. I hope that is not a bug of EclipseLink.
Please help.
 
Himai Minh
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I even add this to the Semester Entity class:

But that does not help.
 
Himai Minh
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I tried to add a many-to-many relationship to student and courses:




Now, it can be deployed.
Let me do more work on it tomorrow.
By the way, why the many-to-many relationship is important for the student and course?
I thought the many-to-many relationship is just for student and semester.
 
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Are you creating the tables yourself? Or do you let the persistence provider create them for you?

This is not the primary key that I would expect from that mapping:

PRIMARY KEY (STUDENT, SEMESTER,COURSE);

 
Himai Minh
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I created those tables myself using the SQL statements first before I create the entity classes.
I guess the composite primary key is (student, semester , course) instead of (student, semester) or (student, course).

If I use two columns as the composite key, this key may not be unique. The enrollments join table will be like this for example:
Student   Semester   Course
----------------------------------
1              Spring        JPA
1              Spring        EJB
1              Winter        Servlet
1              Winter        JSF
1              Fall            JSF
1              Summer     JSF

I cannot pick (student, semester) or (student, course) as the composite key because of these reasons:
- a student may enroll in more than one course in one semester or
- a student may repeat the same course in different semesters.
 
Frits Walraven
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Just let the tables be created by the persistence provider and see how it is done.

Hint: use these properties in your persistence.xml:
 
Himai Minh
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Hi, Frits.
Thanks for your suggestion.
I use the JPA provider to create the tables, course, student, semester and enrollment.
In the enrollment table, the three columns : student, course and semester are a composite of primary keys.
 
Himai Minh
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Let me add one more comment on my previous post:


If I use two columns as the composite key, this key may not be unique. The enrollments join table will be like this for example:
Student   Semester   Course
----------------------------------
1              Spring        JPA
1              Spring        EJB
1              Winter        Servlet
1              Winter        JSF
1              Fall            JSF
1              Summer     JSF



Course is a key of a hash map and it must be unique. So, there is no possibility that student 1 can take JSF course more than once.
So, I think the composite primary key should be student and course.
But when the join table is generated, the composite primary key is student, course and semester.
 
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