Hibernate version:
3.2

I have several tables containing only id/name pairings and would like to map the child table to its parent but, instead of returning the parent entity, i'd like to return a property of the parent entity.

Is this possible?

I understand that I could just map the table and the create a method in child like

String getMIMEType()
{
return mime.getTypeName();
}

This is quite trivial to do, but I would like to avoid the mappings if possible, as I have many of these types of tables.


Thanks.

You might be able to solve this by joins. Look at section 5.1.18 of the online documentation.


Farzad-

Hi, thanks for the reply.

If I use join in the child table's config, then Hibernate will treat is as the parent. The join would need to be used in the mimeTable's config (which is a table i'd rather not map).

In this example A is the child.


create table A (
id integer not null auto_increment,
type integer not null,
primary key (id)
) type=InnoDB;


create table mimeType (
contentTypeId integer not null,
contentType varchar(255),
primary key (contentTypeId)
) type=InnoDB;


alter table A
add index FKTYPE (type),
add constraint FKTYPE
foreign key (type)
references mimeType(contentTypeId);


<class name="A">

<id name="id" type="integer">
<generator class="native"/>
</id>

<join table="mimeType">
<key column="contentTypeId"/>
<property name="contentType"/>
</join>

</class>

public class A {
//...

public void setContentType(String type) {
this.type = type;
}

public String getContentType() {
return type;
}

}

Generates:

[java] Hibernate:
[java] select
[java] a0_.id as id0_0_,
[java] a0_1_.contentType as contentT2_1_0_
[java] from
[java] A a0_
[java] inner join
[java] mimeType a0_1_
[java] on a0_.id=a0_1_.contentTypeId
[java] where
[java] a0_.id=?

Ok you lost me here. Can you rephrase your problem? In other words, can you tell me what you expect to happen in your example?

Hi, ok, so what I want is to do is relate A to the mimeType, providing only a getter in A for a property of mimeType, without mapping mimeType.

I have several constant tables containing only key/value pairs, and would like to avoid mapping them, if possible.

Given the mapping:

<class name="A">

<id name="id" type="integer">
<generator class="native"/>
</id>

<join table="mimeType">
<key column="contentTypeId"/>
<property name="contentType"/>
</join>

</class>

I would have wanted this to create the following query:

select A.id, mimeType.contentType from A inner join mimeType on mimeType.contentTypeId = A.type

Subsequently, the A entity would be populated with the contentType column.

Instead the join element
causes the mimeType table to be treated as the child in the relationship, which it is not.

Thanks

I see your point now. You are right. Joins are not made for this. However, you might still be able to use joins if you are not going to update your object. Nonetheless, it is not very performance efficient if most of those key-value pairs are constant. If so, you might want to define a new entity for each of them and cache them in memory and you will have a better performance. In any case, I can't come to any other idea now. Lets see if anyone else has a solution for this.

My ++1 cents
Farzad-