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UID generation for composite key

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chak

Post subject: UID generation for composite key

Posted: Mon Aug 09, 2004 10:32 am

Newbie

Joined: Tue Aug 03, 2004 11:34 am
Posts: 8

I, i'm using hibernate version 2.1.4,
I am currently migrating to hibernate.
I'm very intersted in using UID generation feature of hibernate for generating a part of a primary key.(

Code:

mapping element).

But the mapping where i need such a feature contains a composite key.
Here is the mapping:

Code:

<hibernate-mapping>
    <class
        name="com.atronicsystems.database.data.MessageHistory"
        table="SHISMSG"
        dynamic-update="false"
        dynamic-insert="false"
    >

        <composite-id
            name="id"
            class="com.atronicsystems.database.data.MessageHistoryId"
        >
                     <key-property
                        name="casinoId"
                        type="java.lang.Integer"
                        column="ID_CASINO"
                        length="10"
                />

                     <key-property
                        name="messageId"
                        type="java.lang.String"
                        column="ID_MSG"
                        length="21"
                />

        </composite-id>

....

I'cant change the primary key, it has to be a composite key!
But i had for each new record to generate a unique id for the

Code:

messageId

property (

Code:

casinoId

property is known).
So if i can't use the generate element in my composite key for the message id attribute, is there a way to use one of the generator algorithm outside of the mapping.
In order for me to set the

Code:

messageId

attribute with a unique id generated by hibernate. (I don't want to rewrite a generator algorithm code :-( ).

Does anyone have a solution?

Thanks for your help.

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VampBoy

Post subject:

Posted: Mon Aug 09, 2004 11:34 am

Expert

Joined: Sat Jan 17, 2004 2:57 pm
Posts: 329
Location: In the basement in my underwear

If you are generating a UUID, why not just use THAT as your PK rather than having it as a composite?

You can still enforce a unique constraint on the DB side if it makes business sense.

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steve

Post subject:

Posted: Mon Aug 09, 2004 12:58 pm

Hibernate Team

Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
Location: Austin, TX

Id generators are not supported for composite ids. Composite ids must be assigned.

As part of assigning that id, sure you can manually instantiate and use one of the id generators.

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ernst_pluess

Post subject:

Posted: Mon Aug 09, 2004 3:31 pm

Expert

Joined: Thu Jan 29, 2004 2:31 am
Posts: 362
Location: Switzerland, Bern

If you're using the DAO pattern, you can provide a create() Method on the DAO, which does the id assignment. This way you don't have to do it in the business logic.

HTH
Ernst

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chak

Post subject:

Posted: Tue Aug 10, 2004 3:47 am

Newbie

Joined: Tue Aug 03, 2004 11:34 am
Posts: 8

VampBoy wrote:

If you are generating a UUID, why not just use THAT as your PK rather than having it as a composite?

You can still enforce a unique constraint on the DB side if it makes business sense.

If i'm not just using the UUID as my PK it's because i'm not authorized to change database architecture (i have to use it like it is).

But is it possible to keep the orginal database architecture (with a composite PK) and to define in my hibernate mapping the UUID (messageId) as my pk and a single constraint on the casinoId.

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chak

Post subject:

Posted: Tue Aug 10, 2004 3:53 am

Newbie

Joined: Tue Aug 03, 2004 11:34 am
Posts: 8

steve wrote:

Id generators are not supported for composite ids. Composite ids must be assigned.

As part of assigning that id, sure you can manually instantiate and use one of the id generators.

That's exactly what i want: manually insantiate and use one of the id generators.

But the point is: how to do this?
Have you some examples?

I see in API documentation that there is a IdentifierGeneratorFactory, but it's use looks to me mysterious.

Thanks a lot.

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chak

Post subject:

Posted: Tue Aug 10, 2004 3:58 am

Newbie

Joined: Tue Aug 03, 2004 11:34 am
Posts: 8

ernst_pluess wrote:

If you're using the DAO pattern, you can provide a create() Method on the DAO, which does the id assignment. This way you don't have to do it in the business logic.

HTH
Ernst

I'm using a DAO, but have you an example about how to do it.

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steve

Post subject:

Posted: Tue Aug 10, 2004 2:20 pm

Hibernate Team

Joined: Tue Aug 26, 2003 3:00 pm
Posts: 1816
Location: Austin, TX

Why use the factory? You just said you use a known id generator. Just instantiate the class representing that generator, and call its generate() method:

Code:

    // UUID generators support a "seperator" property, but its optional...
    Properties props = new Properties();
    props.put("seperator", "-");

    IdGenerator generator = new UUIDHexGenerator();
    generator.configure(props);

    ...

    Object uuid = generator.generate( (SessionImplementor) session, entity );

Note, the UUID generators do not use either of the parameters passed to the generate method. So this is also valid for them:

Code:

Object uid = generator.generate(null, null);

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