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OneToMany with inheritance

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gbondy

Post subject: OneToMany with inheritance

Posted: Wed Jun 23, 2010 4:58 pm

Newbie

Joined: Tue Jun 01, 2010 12:19 pm
Posts: 3

I would like to find a way to form a OneToMany relationship to objects that are retrieved from the child tables of an inheritance structure. For example I have a table, Shape, that represents the super class of the inheritance structure. In the java class for Shape it includes the annotation @Inheritance(strategy=InheritanceType.JOINED). I then have tables that represent the subclasses of Shape, these include Circle, Rectangle and Triangle. The java classes for each of these extend Shape.

I would like to find a way to form a OneToMany from another table/class called DrawingArea with syntax similar to:

Code:

    @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "SHAPEID", nullable = false)
    public List<Shape> getShapes() {
        return shapes;
    }

This would return shapes of all types, Circle, Rectangle and Triangle where the primary key SHAPEID matches. How can I do this?

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gbondy

Post subject: Re: OneToMany with inheritance

Posted: Thu Jun 24, 2010 1:23 pm

Newbie

Joined: Tue Jun 01, 2010 12:19 pm
Posts: 3

I haven't gotten any responses to this post yet. It leads me to believe that there may be a limitation in JPA/Hibernate that doesn't allow this type of relationship to be created with annotations. In absence of an annotated solution for this, I have come up with a way to handle it by persisting the elements from the collection manually. In the DrawingArea class I define the collection of Shapes as Transient.

Code:

   private List<Shape> shapes = new ArrayList<Shape>();
 .
 .
 .
   @Transient
   public List<Shape> getShapes() {
      return shapes;
   }

   public void setShapes(List<Shape> value)
   {
      this.shapes = value;
   }

Then in the DrawingAreaDAO, I manually persist each type from the shapes collection:

Code:

    // These values are autowired by Spring, code not included.
    private ShapeDAO shapeDAO;
    private CircleDAO circleDAO;
    private RectangleDAO rectangleDAO;
    private TriangleDAO triangleDAO;
 .
 .
 .   
    @Transactional 
    public void persist(DrawingArea transientInstance) {
        entityManager.persist(transientInstance);

        // Save all the shapes.
        List<Shape> shapes = transientInstance.getShapes();
        if (shapes != null) {
            for (Shape shape : shapes) {
               if (Circle.class.isAssignableFrom(shape.getClass())) {
                  circleDAO.persist((Circle)shape);
               } else if (Rectangle.class.isAssignableFrom(shape.getClass())) {
                  rectangleDAO.persist((Rectangle)shape);
               } else if (Triangle.class.isAssignableFrom(shape.getClass())) {
                  triangleDAO.persist((Triangle)shape);
               } else {
                  shapeDAO.persist(shape);
               }
            }
        }
    }

I would be very interested to hear comments about this implementation and/or suggestions to improve it.

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