Hi Jeff,The reason that this is done is so you can create an instance of the PageId class without having a persistent (or detached) instance of Book. The way it works now, if you have the id of the Book you can construct an instance of the PageId by also supplying the page number.
If the types matched, you would need to have an instance of Book that had the proper id field set before you could create an instance of PageId. Which would mean that you might have to go to the database twice to get a Page (once to get the Book and another to get the Page).
Another alternative if you want to avoid this "confusion" is to have the Page mapped with a String bookId and int number. But that would mean mapping the bookId column to both the Book relationship and to the primary key. Which has its own set of issues.
Hope this makes sense. It was done deliberately. Craig On Mar 29, 2007, at 9:02 AM, jeff wrote:
thanks pinaki, now i get it :)i must say though that these are confusing semantics. JPA wants me to name the fields and mutators the same between the Page and PageId class, but for them to be different types. imagine an object model with two classes and two methods,Foo.getBlah() Bar.getBlah()where Foo.getBlah() returns a String, and Bar.getBlah() returns an int. not exactly intuitive to the user of such an API.anyway :)Pinaki Poddar <[EMAIL PROTECTED]> wrote: Page can have a primary key field type of "Book".@IdClass(com.mycompany.book.PageId.class) @Entity public class Page { @Id int number; @Id @ManyToOne private Book book; } public class PageId { int number;String book; // the type "String" must match the type of primary keyused in Book.java // the name of the variable "book" must match the name of the variable in Page class. } public class Book { @Id String title; } Pinaki Poddar BEA Systems 415.402.7317 -----Original Message----- From: jeff [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 28, 2007 4:35 PM To: open-jpa-dev@incubator.apache.org Subject: RE: composite ID based on "one" side of a bidirectional one-many relationship hi, abe closed this with the reasoning ..."the book field in the PageId class must be of type String to match theprimary key field type of Book" was i mistaken when i understood you to say that Page could have a PK field of type Book? if not, very sorry for all the confusion. or were you just saying that open JPA allowed the PK field to be a ManyToOne relationship? p.s., it's issue #191 https://issues.apache.org/jira/browse/OPENJPA-191 Patrick Linskey wrote: Yes, please do. It looks like your code should work. -Patrick -- Patrick Linskey BEA Systems, Inc.______________________________________________________________________ _ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return thisby email and then delete it.-----Original Message----- From: jeff [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 28, 2007 10:31 AM To: open-jpa-dev@incubator.apache.org Subject: RE: composite ID based on "one" side of a bidirectional one-many relationship yes, i see the problem w/ the attached classes, and with a completely different model where i am trying to accomplish the same thing. should i file a bug? i can attach the test case there. Patrick Linskeywrote: Are you stillseeing that same problem with the code that you attached? -Patrick -- Patrick Linskey BEA Systems, Inc. ______________________________________________________________ _________ Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary,copyrighted and/or legally privileged, and is intended solely for theuse of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this by email and then delete it.-----Original Message----- From: jeff [mailto:[EMAIL PROTECTED] Sent: Tuesday, March 27, 2007 1:42 PM To: open-jpa-dev@incubator.apache.org Subject: RE: composite ID based on "one" side of a bidirectional one-many relationship Patrick Linskeywrote:my ID class has a book field, and getters and setters for it >to match Page's book field. i wonder about the last line > where itsays "java.lang.String". that seems odd. Can you post your Book and Page classes and the Page's IdClass? attached. i keep trying to attach the entire project as a zip, but apache's spam filter keeps dropping it. let me know i could send to you directly.so, regardless, even if that did work, correct me if i am >wrong, but it'd be a really bad idea to depend on openjpa > specifics, because my app doesn't get to choose the JPA > implementation, it has to use whatever the java ee container > gives it ... right? No -- a Java EE 5 container *must* allow you to specify your persistence provider. Whatever you put in the element in the persistence.xml must be obeyed. Only if you do not specify a element can the implementation can choose whatever it wants to use. yes, duh. sorry. Correct.so, assuming i do need to accomplish this, is there a best >practice? as i mentioned, what i did to make it work was make > thePage's composite ID incorporate the Book's ID by adding a > "derived" bookName field to Page, like ... You could add a private bookName field that has no external mutators or accessors, and create a @PreStore callback that copies the value from the related Book into the field. That would do a decent job of isolating the artifact from the rest of your app. yes, that works. ________________________________ Finding fabulous fares is fun. Let Yahoo! FareChase search your favorite travel sitesFtNW45amVpBF9TAzk3NDA3NTg5BF9zAzI3MTk0ODEEcG9zAzEEc2VjA21haWx0 YWdsaW5lBH NsawNxMS0wNw--> to > find flight and hotel bargains.Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary,copyrighted and/or legally privileged, and is intended solely for theuse of the individual or entity named in this message. 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Games.Notice: This email message, together with any attachments, may contain information of BEA Systems, Inc., its subsidiaries and affiliated entities, that may be confidential, proprietary, copyrighted and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this by email and then delete it.--------------------------------- Sucker-punch spam with award-winning protection. Try the free Yahoo! Mail Beta.
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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