I have 2 tables with one-to-many relationship, ex: student and school.

under the same single open transaction, i create a new instance for each object representing the 2 tables. I add the student instance
to school.getStudents collection.

after i commit the transaction which save the "school" instance, one record is inserted in each of the 2 tables. but the problem is with the student table, value of its school_id column, which is the foreign key to school table, is 0.

can you tell why it works this way?


Thanks,

Do you defined the one-to-many relationship unidirectional or bidirectional (= with inverse owner).
In ladder case, you must also set the relationship on both sides:
not only



also



must be called.

Yes, i wrap these 2 statements inside the open transaction.



I define bidirectional relationship.

You should use the inverse attribute if you want to have the association bidirectional:
http://docs.jboss.org/hibernate/stable/ ... irectional

Ok, the problem is solved now because i put the reverse column name for


But there happens another problem, now the primary key of the foreign table, "Student", has a value of "0" instead of auto incremented value. I've specified the below in the student mapping file, but why it still doesn't work?

It is not a good idea to use the id column as the list index. List indexes usually go from 0 to the number of entries in the list (minus one). I guess the <index column="student_id"></index> mapping overrides the <generator class="increment" /> mapping. You should probably use a <set> mapping instead of <list>. <bag> is also possible but it allows you to enter the same student more than once for a school.

You're so right. yes after changing from List to Set, now it works. Thanks.

According to Hibernate manual, Bag is not good in term of performance. because it doesn't maintain an index column so when a user modify an item in the collection, the whole collection has to be deleted and recreated again.

Is the above statement true? in my example, what collection type best suited in my situation?

Thanks,

But the <many-to-one> in the Student is the owner of the association (or didn't you add the inverse="true" as pb00067 suggested?) so the the <set> will not be used for updates.

I would use a <set> myself because it feels more comfortable and I don't really worry about the performance of code like in the example here: http://docs.jboss.org/hibernate/stable/ ... ientupdate

Thanks so much. I understand better now.