docs: private void checkReferenceForeignkeys(ModelDef modelDef, String checkLevel) throws ConstraintException
      {
          if (CHECKLEVEL_NONE.equals(checkLevel))
          {
              return;
          }
  
          ClassDescriptorDef     classDef;
          ReferenceDescriptorDef refDef;
  
          for (Iterator it = modelDef.getClasses(); it.hasNext();)
          {
              classDef = (ClassDescriptorDef)it.next();
              for (Iterator refIt = classDef.getReferences(); refIt.hasNext();)
              {
                  refDef = (ReferenceDescriptorDef)refIt.next();
                  if (!refDef.getBooleanProperty(PropertyHelper.OJB_PROPERTY_IGNORE, false))
                  {
                      checkReferenceForeignkeys(modelDef, refDef);
                  }
              }
          }
      }