Hi,

I've found a big issue with Hibernate 3 (using annotations). I'll try to explain it with a little example.

I have a table with a composite key of four columns. One of such columns is an auto-increment column:

CREATE TABLE IF NOT EXISTS `bdprueba`.`extensions` (
`id` BIGINT(20) UNSIGNED NOT NULL AUTO_INCREMENT ,
`context` VARCHAR(40) NOT NULL DEFAULT '' ,
`exten` VARCHAR(40) NOT NULL DEFAULT '' ,
`priority` INT(11) NOT NULL DEFAULT '0' ,
`app` VARCHAR(40) NOT NULL DEFAULT '' ,
`appdata` VARCHAR(256) NOT NULL DEFAULT '' ,
PRIMARY KEY (`id`, `context`, `exten`, `priority`) )
ENGINE = MyISAM
AUTO_INCREMENT = 11
DEFAULT CHARACTER SET = latin1;


With the following class mapping (+ composite pk class):


package ext;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.IdClass;
import javax.persistence.Table;

import com.sun.istack.internal.NotNull;

@Entity
@Table(name = "extensions")
@IdClass(ExtensionPK.class)
public class Extension implements Serializable {



public Extension(String context, String extension, int priority) {
super();
this.context = context;
this.extension = extension;
this.priority = priority;
}



@Id
@Column(name = "id")
@GeneratedValue(strategy = GenerationType.TABLE)
private int id;

@Id
@NotNull
@Column(name = "context", length = 40)
private String context;

@Id
@NotNull
@Column(name = "exten", length = 40)
private String extension;

@Id
@NotNull
@Column(name = "priority")
private int priority;

@NotNull
@Column(name = "app", length = 40)
private String application;

@NotNull
@Column(name = "appdata", length = 256)
private String applicationData;

[gets and sets]

}



@Embeddable
public class ExtensionPK implements Serializable {

public ExtensionPK() {
super();
}


@NotNull()
@Column(name = "id")
private int id;

@NotNull()
@Column(name = "context", length = 40)
private String context;

@NotNull
@Column(name = "exten", length = 40)
private String extension;

@NotNull
@Column(name = "priority")
private int priority;

[.. gets and sets]

}

With this mapping, the persistence of an 'Extension' object works well. However, I need to know the key assigned to the 'id' attribute after an extension is stored (o.getId()), but surprisingly it's always 0!. This works well when I have a single primary key (I mean, after storing an object with an auto-generated key, I can know the assigned id just by checking the attribute).

Anybody know what may be the problem?, My real scenario is with a more complex dbmodel. I need to know the assigned value of an element of a composite-pk (after saving its related object) to be able to create other related composite-pk-objects. I simply don't want to query the object again (by this way, the pk-values are stored on the object correctly).

Thanks in advance!

Héctor

I don't think Hibernate has support for generated composite keys. The documentation at http://docs.jboss.org/hibernate/stable/ ... ompositeid says:

Hi Nordborg, thanks for your reply, and specially thanks for your documentation's reference.

Let me propose additional questions...

- about this limitation, can't it be considered as a Hibernate's big issue?, because this framework is supposed to do everything that can be done with the old JDBC and SQL!... and I don't like the idea of alter my DB model or forget RDBMS features just because ORM limitations.
- What could be the best approach to handle this scenario?... I mean, ¿what could be the best strategy for the application to assign identifiers by itself?, are there any application-based key-generation strategy safe for concurrency?
- Somebody suggest me to use 'GenerationType.IDENTITY' as generation strategy, but with no more details. Is it right?


Thanks,
Héctor