java - hibernate 中的 saveOrUpdate() 问题

Question

最近我开始使用hibernate。插入或更新我正在使用 saveOrUpdate() 函数。如果我更新一个条目，我工作正常。但是，随着新条目 hibernate 生成一个查询。但是表中没有任何更新。

我的场景是这样的，

我在两个表之间使用多对一和一对多关系[Expense, Category]对于更新或插入，我正在创建两个对象(Expense expense, Category category)客户端。在服务器端，我将 category 对象设置为 expense 对象。

public void upDateExpenseTable(Expens expense, Category category) {

    expense.setCategory(category);
    Session session = Main.getSession();
    try{
        System.out.println("Inside Update Try Block");
        session = Main.getSession();
        Transaction tr = session.beginTransaction();
        session.saveOrUpdate(expense);
        tr.commit();

    }
    finally{
        session.close();
    }
}

对象结构如下，catogery.catId, category.catName &expense.expnsId, expense.expnsName, expense.amount, expense.status, expense.userName.

但是 Expense 表 cat_id 中还有一列。它是通过映射注释。但是我在 Expense 实体中没有任何属性(property)。插入新数据时，我没有提供任何 Id。

任何建议!!!

public class Expens implements Serializable {
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int expnsId;
private int amount;
private String date;
private String status;
private String userName;

    @ManyToOne
@JoinColumn(name = "cat_id") 
private Category category;
    //Setter Getter

}

类别类

public class Category{
private static final long serialVersionUID = 1L;

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private int catId;
private String catName;

@OneToMany(targetEntity=Expens.class, mappedBy = "category", cascade = CascadeType.ALL, fetch=FetchType.EAGER)
private List<Expens> expenses;
}//Setters Getters ommited.

Answer 1

我不确定我是否理解所有内容，但我至少可以告诉您，您没有正确构建双向关联，您需要在以下情况下设置“链接的两侧”构建你的对象图:

...
expense.setCategory(category);
category.getExpenses().add(expense);
...
session.saveOrUpdate(category);

这通常在“链接管理”方法中完成，像这样(在 Category 中):

@Entity
public class Category {

    @Id @GeneratedValue(strategy=GenerationType.AUTO)
    private int catId;
    private String catName;

    @OneToMany(targetEntity=Expens.class, mappedBy = "category", cascade = CascadeType.ALL, fetch=FetchType.EAGER)
    private List<Expens> expenses = new ArrayList<Expens>();

    public void addToExpenses(Expense expense) {
        expenses.add(expense);
        expense.setCategory(this);
    }    

    protected List getExpenses() { // protected to prevent direct access from outside the hierarchy
        return expenses;
    }

    protected void setExpenses(List expenses) { // protected to prevent direct access
        this.expenses = expenses;
    }

    //...
}

代码变为:

category.addToExpenses(expense);
session.saveOrUpdate(category);

有趣的是(或不是)，我今天已经写了三篇关于这个的文章。

资源

• Hibernate 核心文档
  • 1.2.6. Working bi-directional links