composite-id, one-to-one mapping, no constraints in database

PatrickKik · **Posted:** Tue Jan 20, 2009 6:44 am

I'll be short. I'm using Hibernate 3. My problem is about one-to-one mapping with composite-id's (I think). None of the examples I have seen so far are the same as my situation.

Goal

Without any mapping in the database itself, being able to do:

Code:

Apple apple = // retreive apple from Hibernate
String juice = apple.getOrange().getJuice();

Problem

org.hibernate.TypeMismatchException: Provided id of the wrong type. Expected: class fruit.Orange, got class fruit.Apple

Why does it not work? He should expect an Orange in the mapping, but why is there an Apple?

Database

I have two tables without any foreign key constraints. For APPLE the primary key is number and subnumber. For ORANGE the primary key is nr and subnr.

APPLE (number, subnumber, color)
ORANGE (nr, subnr, juice)

Mapping

Code:

<class name="fruit.Apple" table="APPLE">
  <composite-id>
    <key-property name="number" column="number" type="long" />
    <key-property name="subnumber" column="subnumber" type="int" />
  </composite-id>
  <one-to-one name="orange" class="fruit.Orange" />
</class>

Code:

<class name="fruit.Orange" table="ORANGE">
  <composite-id>
    <key-property name="number" column="nr" type="long" />
    <key-property name="subnumber" column="subnr" type="int" />
  </composite-id>
</class>

Java

Code:

public class Apple {
  private long number;
  private int subnumber;
  private Orange orange;
  // getters and setters
}

Code:

public class Orange {
  private long number;
  private int subnumber;
  // getters and setters
}

mmerder · **Posted:** Tue Jan 20, 2009 6:58 am

This happens, because you do not have an ID-Class in your mapping. In that case, objects itself are the identifier. No problem so far, but you have an OneToOne-association: these are normally mapped using the primary key also as the foreign key. So hibernate uses Apple's primary key (an apple) as foreign key to load orange (which wants an orange).

To avoid this, create an IdClass, which has the Id-Attributes as properties:

Code:

public class FruitId {
  private long number;
  private long subnumber;
  //Getters, Setters
}

Now in your mapping just add the class attribute to your composite-id:

Code:

<composite-id class="FruitId"> ...

That should solve this problem. See also the second approach here (and if you understand German look here for a topic relating the same issue).

PatrickKik · **Posted:** Tue Jan 20, 2009 10:56 am

Thank you, mmerder. It turned out I was on the right track, but the Orange-view turned out to be empty! :S So it took me some more time than needed... But your post was helpful.

CatchSandeepVaid · **Joined:** Wed Aug 22, 2007 5:53 am **Posts:** 38

I also have the same problem...
I tried with the approach of having a seperate class for Composite-Id.. I have one-to-one relationship between Product and Product-Id..

I have Product (PId, PDesc) as composite-key
I have ProductBasic (ProductId, ProductDesc) as composite-Key

Case 1: I created one Composite class which is common for both Product and ProductBasic..
class CompProductRelated{
string pid;
string pdesc;
}
then try to fetch Product.. It worked !!!

Case 2: If i create seperate Composite class for Product & ProductBasic viz. CompProduct and CompProductBasic respectively as :

class CompProduct{
string productId;
string productDesc;
}

and not if i define the mapping accordingly as:
In Product.hbm.xml
<composite-id name="compProduct" class="CompProduct">
<key-property name="pid" type="string" column="PRODUCTID" length="10"></key-property>
<key-property name="desc" type="string" column="DESC" length="10"></key-property>
</composite-id>

In ProductBasic.hbm.xml
<composite-id name="compProductBasic" class="CompProductBasic">
<key-property name="productId" column="PRODUCTID" type="string" length="10"/>
<key-property name="productDesc" column="DESC1" type="string" length="10"/>
</composite-id>
Now while fetching Product, it gives the following exception:
org.hibernate.TypeMismatchException: Provided id of the wrong type. Expected: class model.CompProductBasic, got class model.CompProduct

NOTE: This is the similar exception if i don't use a seperate class for CompositeId..

I think this hibenate restriction (of having common CompositeId class for one-to-one relationship) is not good as it puts a constraint on how domain model (java) should be which could not be possible everytime in legacy applications..