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From T E Schmitz <mail...@numerixtechnology.de>
Subject Re: doSelect with collections filled
Date Thu, 02 Sep 2004 10:55:24 GMT
Hello Artur,

Artur Z wrote:

>>    Did you defined the foreign key relationship beetwen  Author and
>>Book in your schema file?
>>If yes, there should be protected method in BaseAuthorPeer
>>doSelectJoinBooks() (or something like that). Write this method as
>>public in AuthorPeer
>>and than you can use it.

> yes, I defined, but there is no such method
> torque generated only method BaseBookPeer.doSelectJoinAuthor(...)
> as far as I know torque generates only methods for accessing associations
> (one), but not collections

There is no one SQL statement that would return you an author tuple and 
n tuples for his related books.

> if you want to access a collection you call author.getBooks(), and it reads
> books from db, caches it and returns - it couses perfirmance issues (one db
> call for each getXXXs() method)
> how to solve it ?
> how to query author table to get in return list of authors with ALREADY
> INITIALIZED books collections ?

If you take a close look at BaseBookPeer.doSelectJoinAuthor() you will 
find that this method not only sets the Author for each book but it also 
builds up the Authors' Book collections. In BaseAuthor.java there is a 
method called something like addBook(), which is called in the 
doSelectJoinXXX loop.

The only way you can select all authors and their books in one SQL 
statement is by selecting all books joined with author (possibly ordered 
by author). If using Torque that means BaseBookPeer.doSelectJoinAuthor(...).
If you don't want to select all books, just certain authors, you have to 
pre-set the criteria argument for doSelectJoinXXXX. If you add an 
OrderBy Author to Criteria, you will get a list of books sorted by authors.

I presume each book has an author, in which case the generated inner 
join will do you.

> I found one solution in
> http://www.mail-archive.com/torque-user@db.apache.org/msg01712.html
> but is not handy and you operate on array of objects, not getXXXs() methods
> and collections

This example is pretty much a copy of doSelectJoinXXXX. To translate 
this to your example, this would produce something like 
BaseBookPeer.doSelectJoinAuthor(...): read all books pre-fileld with 
their Authors.



Tarlika Elisabeth Schmitz

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