解决 Java.lang.ClassCastException

Question

我在休眠中很新。我真的陷入了Java.lang.ClassCastException问题。一整天都无法解决我下面的代码的这个问题。任何人都可以帮助我吗？@Overridepublic ObservableList<Product> getSold() {    ObservableList<Product> list = FXCollections.observableArrayList();    Transaction tx=null;    session = Hibutil.getSessionFactory().getCurrentSession();    try {        tx= session.beginTransaction();        List<Product> productList = session.createQuery(" select productName, count(productName) as totalSold  from Product where sell='1' group by productName Order by totalSold desc").setCacheable(true).list();        tx.commit();        productList.stream().forEach(list::add);// getting error here        System.out.println(list.get(0));        return list;    } catch(HibernateException e) {        if(tx!=null)tx.rollback();        return null;    }我已阅读此内容，但无法解决此问题。

Answer 1

I suppose you are getting error at this line:

List<Product> productList = session.createQuery(" select productName, count(productName) as totalSold  from Product where sell='1' group by productName Order by totalSold desc").setCacheable(true).list();

You need to write DTO for this.

class ProductDto {

private ProductName;

int productCount;

//getters and setters and constructors

}

you can accordingly modify the query as:

List<ProductDto> productDtoList = session.createQuery(" select new ProductDto (productName, count(productName))  from Product where sell='1' group by productName order by count(productName) desc").setCacheable(true).list();

Answer 2

我不明白如何将查询的结果转换为 Product 实例，特别是在选择中包含 count() 。

我会更改查询的以下部分

select productName, count(productName) as totalSold from Product

对此

SELECT * FROM Product

（也许用实际的列名替换 * ）