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POHibernate many to many with a composite key with one field shared on either side of the relationship
 

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  1. POHibernate many to many with a composite key with one field shared on either side of the relationship
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    <p>This is a conceptional example, but I do not understand how to implement this.</p> <p>I have tables as follows:</p> <pre><code>BOOK ------------ BOOK_ID BOOK_AUTHOR ------------ BOOK_ID AUTHOR_ID AUTHOR ------------ AUTHOR_ID </code></pre> <p>Which map to the following hibernate many to many relationship:</p> <p>Book</p> <pre><code>@Entity public class Book implements Serializable { @ManyToMany( targetEntity=org.hibernate.test.metadata.manytomany.Author.class, cascade={CascadeType.PERSIST, CascadeType.MERGE} ) @JoinTable( name="BOOK_AUTHOR", joinColumns=@JoinColumn(name="BOOK_ID"), inverseJoinColumns=@JoinColumn(name="AUTHOR_ID") ) public Collection getAuthors() { return authors; } } </code></pre> <p>Author</p> <pre><code>@Entity public class Author implements Serializable { @ManyToMany( cascade = {CascadeType.PERSIST, CascadeType.MERGE}, mappedBy = "authors", targetEntity = Book.class ) public Collection getBooks() { return books; } </code></pre> <p>} </p> <p>However, I live in a world where, a book and an author must have matching publishers but a book can exist without an author and an author can exist without a book. So, to my tables I have added a publisher id:</p> <pre><code>BOOK ------------ BOOK_ID PUBLISHER_ID BOOK_AUTHOR ------------ BOOK_ID AUTHOR_ID PUBLISHER_ID AUTHOR ------------ AUTHOR_ID PUBLISHER_ID </code></pre> <p>This in the database layer, would mean that the publisher id must match across all three tables meaning a book and author must have the same publisher, but how do I implement this using hibernate mapping?</p>
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    1. USmogronalol
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    1. COSo Book and Author both have a Publisher field that is optional. But why do you need to add PUBLISHER_ID in the join table?
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      1. USoksayt
    2. CObecause the book and author must have the same publisher in order to relate to each other in the BOOK_AUTHOR table, enforced by a composite key
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