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From "Patrick Linskey" <plins...@bea.com>
Subject RE: composite ID based on "one" side of a bidirectional one-many relationship
Date Tue, 27 Mar 2007 17:40:26 GMT
> i want the Page's ID to be based on it's number, and ALSO the 
> owning Book's name. i could make an ID class for Page, but 

If you wanted to make the ID be based on it's number and the owning Book
itself (i.e., not the name), you could do this with OpenJPA, but not
with vanilla JPA. OpenJPA supports @Id fields on one-to-one and
many-to-one fields:
http://incubator.apache.org/openjpa/docs/latest/manual/manual.html#ref_g
uide_pc_oid_entitypk

Personally, I think thaht using the Book object as part of the PK is
probably a better idea than using the Book's name, since it seems like
the Book's name is not unique.

However, if you really do want to use the Book's name, the only way to
do so in OpenJPA is to make Book.name the @Id of the Book class, and use
the syntax in the link I provided above.

-Patrick

-- 
Patrick Linskey
BEA Systems, Inc. 

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> -----Original Message-----
> From: jeff [mailto:jeffrey.blattman@yahoo.com] 
> Sent: Tuesday, March 27, 2007 10:08 AM
> To: open-jpa-dev@incubator.apache.org
> Subject: composite ID based on "one" side of a bidirectional 
> one-many relationship
> 
> say i have Book and Page classes. a Book has a name and can 
> also have many Pages. a Page has a number, and a reference to 
> the owning Book.
> 
> i want the Page's ID to be based on it's number, and ALSO the 
> owning Book's name. i could make an ID class for Page, but 
> the fields of the ID class need to be simple types, so i 
> can't map them to the book field in Page ... ?
> 
> i did get it to work by adding a bookName field to Page that 
> gets populated in the setBook() setter, and creating a PageId 
> that uses the Page's number and the simple bookName field. 
> 
> however, this seems wrong, as it results in redundant data 
> stored in the Page table. for example, the created table for 
> Page has  NUMBER, BOOKNAME, and BOOK_BOOK_NAME columns, the 
> latter two of which are always the same. 
> 
> i am sure there's a best practice for this. any advice is appreciated.
> 
> i have a test case for this i can send if my description is 
> not obvious, but my last attempt failed apache's spam filter. 
> 
> 
> 
>  
> ---------------------------------
> Don't get soaked.  Take a quick peek at the forecast 
>  with theYahoo! Search weather shortcut.
> 

Notice:  This email message, together with any attachments, may contain information  of  BEA
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