EJB3/JPA and versioning
- From: guigouz <guigouz@xxxxxxxxx>
- Date: Mon, 24 Sep 2007 20:31:28 -0000
Hello, I'm thinking about a structure which starts as simple as
Book hasMany Page
But Page is not an ordinary entity, it's primary key is composite, and
has (id, version). Everytime I save a Page, it doesn't update it, but
instead increments version and saves it (same id).
Now when I fetch a Book, it should return all Pages, at their lastest
versions. So, the table layout would look like the following, if we
imagine 3 pages
page_id, version, content
1 1 *
1 2 **
1 3 *
2 1 ###
3 1 ##
3 2 &&&&
To add a bit more complexity, a Page may belong to more than one book.
So, for two Books, I'd have a book_pages table with
book_id, page_id
1 1
1 2
2 1
2 3
This way Book 1 has pages { 1, 2 }, and book 2 has pages { 1, 3}. For
the versioning
- When I findByBookId(1) i'd get pages { (1,3), (2,1) } - Page 1
Version 3, Page 2 version 1
- When I findByBookId(2) i'd get pages { (1,3), (3,2) } - Page 1
Version 3, Page 3 version 2
Or, every page on their lastest version. I guess it's pretty close to
what ThingDB from the Open Library project offers (altough they use
python). More info at http://demo.openlibrary.org/about/tech
Anyone think it would be possible to implement such layout using JPA ?
Or maybe I should stick to plain JDBC with custom DAOs ?
Thanks a lot
Gui
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