JPA and hibernate specification error

zhamdi · **Posted:** Thu Nov 15, 2007 9:35 am

Hibernate version: 3.2.3

Hi all,

I have a specification bug (not a functional one):

My example is very pedagogic: I have formulas (in groovy, java, ruby etc...) that may need each others in execution time. For tha purpose I made an object that can declare needed formulas. Each formula is in its own row. So a forumla can have be used in many other formulas, and can have many formulas it invokes: this is our many to many relathionship of Formula on itself.

Now formulas are classed in categories: let's say salary formulas and invoice formulas. Both have the same phylosophy.

Let's look at the formula class (uninteresting methods were removed):

Code:

@MappedSuperclass
public class Formula<F extends Formula>
      implements Serializable {
   protected Set<F>               nestedFormulas, parentFormulas;
   protected long                  id;

   @ManyToMany
   @JoinTable(name = "nested_formulas", joinColumns = @JoinColumn(name = "parent_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "child_id", referencedColumnName = "id"))
   public Set<F> getNestedFormulas() {
      return nestedFormulas;
   }

   @ManyToMany(mappedBy = "nestedFormulas")
   public Set<F> getParentFormulas() {
      return parentFormulas;
   }

With this code, it is obvious that we will have our subclasses this way:

Code:

@Entity class SalarayFormula extends Formula<SalarayFormula> {}

Code:

@Entity class InvoiceFormula extends Formula<InvoiceFormula> {}

Generating the schema I realize there is one and only table nested_formulas with foreign keys on both SalarayFormula and InvoiceFormula. S it can't work because there is no "strategy" expression and no discriminator in the table or any other way to know if a many to many row is concerning this or that subclass entity.

There's an easy workaround (writing the dependencies in children classes but the specification should allow us to say: "I'd like to have one class for each dependency, or Id like tohave tem joined with a discrinatorstraegy"...

Any idea about doing things better?

Regards,
Zied Hamdi