dt = stock.getStockCategories().getById(7).getCreatedDate();

   session.beginTransaction();
 
    Stock stock = new Stock();
    stock.setStockCode("7052");
    stock.setStockName("PADINI");
 
    //assume category id is 7
    Category category1 = (Category)session.get(Category.class, 7);
 
    StockCategory stockCategory = new StockCategory();
    stockCategory.setStock(stock);
    stockCategory.setCategory(category1);
    stockCategory.setCreatedDate(new Date()); //extra column
    stockCategory.setCreatedBy("system"); //extra column
 
    stock.getStockCategories().add(stockCategory);
 
    session.save(stock);
 
    session.getTransaction().commit();