Re: Circular Dependencies and Bidirectional Relationships

[Craig L Russell]

Hi Geoffrey,












Hope this helps,

Craig

On Aug 3, 2007, at 10:21 AM, Geoffrey Downs wrote:

The two cases below are handled naturally as part of ORM. While they are circular relationships in the Java object model, they are not circular in the schema. My experience is that best practice does not exclude circular references among classes *in the same package*. Circularity among classes in different packages is a separate issue. For the Book/Author relationship, a join table is used to associate books with authors. The collection on both sides is mapped to the join table. The join table contains two columns, one that is a foreign key to Book and the other a foreign key to Author. For the Publisher/Magazine relationship, a foreign key in Magazine refers to the Publisher, and this foreign key is also used to map the Collection<Magazines> field of Publisher. The tricky part is managing the Java relationships. Currently, JPA requires that the object model be consistent in memory before you commit. Which means that you need to do both: author.books.add (newBook) and newBook.authors.add(author) before committing. Similarly, you need to do both publisher.magazines.add(newMag) and newMag.publisher=publisher.

Hi all,
  I have a question concerning best practices for implementing

or containment relationships in openJPA?

For example: consider the Book-Author relationship (many-to-many,


   class Book{
      private Collection<Author> authors;
      ...
   }
   class Author{
      private Collection<Book> books;
      ...
   }


and that the class Author also depends on the class Book. Has anyone

etc.?

Example: consider a containment relationship, such as the
Magazine-Publisher relation (Publishers have multiple magazines, every

look like:

   class Magazine{
      private Publisher publisher;
      ...
   }
   class Publisher{
      private Collection<Magazine> magazines;
      ...
   }

Again, this introduces a circular dependency between the Magazine and

that the Magazine class should not know about it's parent Publisher
instance. However, this would result in a database schema that did not

had no association with a publisher object.



Thanks,
-Geoff Downs

bidirectional relationships in openJPA. I am working on a new development project that is evaluating using openJPA as our ORM solution. Architectural coherence is fundamentally important to the project, so we'd like to avoid circular dependencies in our java classes whenever possible. My question is: how do we avoid circular dependencies when dealing with bidirectional bidirectional). The corresponding Java classes might look something like: Unfortunately, this means that the class Book depends on the class Author, developed a best-practice for how to circumvent this? Perhaps creating a BookAuthor relationship class would be a viable option? How would this work within the context of openJPA's features like dirty checking, cascades, magazine has exactly one publisher). The corresponding Java classes might Publisher classes. We could remove this circular dependency by asserting reflect reality: we could easily create "orphaned" magazine objects that Any thoughts on how to resolve these issues would be creatly appreciated.

Craig Russell
Architect, Sun Java Enterprise System http://java.sun.com/products/jdo
408 276-5638 mailto:[EMAIL PROTECTED]
P.S. A good JDO? O, Gasp!

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