Re: Need some in Hibernate

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer,comp.lang.java.help,comp.lang.java.databases

Date:

Wed, 26 Mar 2008 09:50:52 -0400

Message-ID:

<GZmdndS60oghyXfanZ2dnUVZ_vWtnZ2d@comcast.com>

RC wrote:

Hello there,

I am new in Hibernate. I look at some examples in Hibernate 3.2
There is ALWAYS a Long id in a table class, like

public class State {
    private Long id; // no such column in my STATE table in database
    private String state_code; // two-character state code
    private String state_name;

    then six pairs of getXXX/setXXX();
}

My question is my existing table in database has NO id column.
I am NOT allow to altering the existed table.

How do I do the mapping (How do I re-write my XML mapping file)?
Thank Q very much in advance!

Apply the name attribute of the id tag in the mapping table to whatever the
primary key actually is. By defining a generator, you are asking Hibernate to
generate the primary key for you, obviously not in accordance with the table's
design.
<http://www.hibernate.org/hib_docs/v3/reference/en/html/mapping.html#mapping-declaration-id>

If it's a multi-column key, you'd need
<http://www.hibernate.org/hib_docs/v3/reference/en/html/mapping.html#mapping-declaration-compositeid>

The Hibernate folks suggest:

There is an alternative <composite-id> declaration to allow access to
legacy data with composite keys. We strongly discourage its use for anything else.

I do not get what all this is about "legacy data" and "discourage its use".
It's quite common and proper for tables to have multi-column keys.

I haven't run across that editorial outlook in JPA articles (Java Persistence
API), for all that JPA is largely based on Hibernate.

--
Lew