how to use @ManyToOne with composite keys

olak · **Joined:** Wed Jan 31, 2007 6:54 am **Posts:** 22

Hi,
I have two hopefully simple questions concerning how to use relations together with annotations and composite keys.

Hibernate version:
Core 3.2.2GA, Annotations 3.2.1

I have two tables, Company and Platform, where a Company can have many platforms.

Company has the PK companyID, while Platform has a composite PK: (companyID (FK), PlatformID)

I set my classes up like this (stripped from constructors and setters and non-required fields):

Company:

Code:

@Entity
public class Company implements Serializable
{
   private int mCompanyID;
   private Set<Platform> mPlatforms;

   @Id
   public int getCompanyID()
   {
      return mCompanyID;
   }

   @OneToMany(mappedBy="company")
   public Set<Platform> getPlatforms()
   {
      return mPlatforms;
   }

   public void setPlatforms(Set<Platform> aPlatforms)
   {
      mPlatforms = aPlatforms;
   }
}

Platform:

Code:

@Entity
public class Platform implements Serializable
{

   //Columns
   private PlatformPK mComp_id;

   @Id
   public PlatformPK getComp_id()
   {
      return mComp_id;
   }

   private Company mCompany;
   @ManyToOne(cascade = CascadeType.ALL)
   @JoinColumns({
         @JoinColumn(name="companyID", referencedColumnName="companyID", insertable = false, updatable = false)
         })
   public Company getCompany()
   {
      return mCompany;
   }

   public void setCompany(Company aCompany)
   {
      mCompany = aCompany;
   }
}

PlatformPK:

Code:

@Embeddable
public class PlatformPK implements Serializable
{
   private int mCompanyID;
   private int mPlatformID;

   public int getCompanyID()
   {
      return mCompanyID;
   }

   public int getPlatformID()
   {
      return mPlatformID;
   }
}

First, why does the @ManyToOne in Platform have to be insertable = false, updatable = false? I have looked under references with composite key in the manual and doesnt find this there.

Second, if I insert some companies and platforms, I want to fetch the company from a platform:

session.beginTransaction();
Platform platform = (Platform)session.load(Platform.class, new PlatformPK(1,1));
Company company = platform.getCompany();
System.out.println(company.getCompanyID());
session.getTransaction().commit();

If I do this, shouldnt hibernate automatically fetch the company for me?
This seems to be not the case, and by looking in the console, nothing happens on the platform.getCompany() line (debug outputlevel), and I get a NPE on the following line. Am I missing something?

(I also generate schema with hbm2ddl and the tables/relations seems to be set up correctly, using HSQLDB)
thanks in advance!

olak · **Joined:** Wed Jan 31, 2007 6:54 am **Posts:** 22

Hi,
I solved the second question, the assocaition does not become active before the session is closed and reopened. but my first question still applies.
(btw, these pages are always slow on loading here, is this usual?)

emmanuel · **Posted:** Wed Feb 07, 2007 8:26 pm

because otherwise hibernate would have to update the same column with potentially 2 different piece of information

Note that the many to one could be embedded in the id class