Question

我有两个班级：

Employee.java

@Entity
@Table
public class Employee {
    @Id
    @GeneratedValue
    private Long id;

    private String name;

    @ManyToOne
    private Department department;

    public Employee() {}

    public Employee(String name, Department department) {
        this.name = name;
        this.department = department;
    }


    public Employee(String name) {
        this.name = name;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Department getDepartment() {
        return department;
    }

    public void setDepartment(Department department) {
        this.department = department;
    }

    @Override
    public String toString() {
        return "Employee [id=" + id + ", name=" + name + ", department="
                + department.getName() + "]";
    }

}

Department.java

@Entity
@Table
public class Department {

    @Id
    @GeneratedValue
    private Long id;


    private String name;

    @OneToMany(mappedBy="department",cascade=CascadeType.ALL)
    private List<Employee> employees = new ArrayList<Employee>();

    public Department() {
        super();
    }
    public Department(String name) {
        this.name = name;
    }
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public List<Employee> getEmployees() {
        return employees;
    }
    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }
}

然后我尝试在主要方法中保存department和employees：

Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();

Department department = new Department("java");
//session.save(department); //throw org.hibernate.TransientObjectException if I comment the line

session.save(new Employee("Jakab Gipsz",department));
session.save(new Employee("Captain Nemo",department));

session.getTransaction().commit();

它没有用。它抛出了一个错误：

org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: com.learn.hibernate.Department

但如果我取消注释行session.save(department);，一切正常。为什么？我已经设置了cascade=CascadeType.ALL，因此应该自动保存department而不会丢失任何错误。我错过了什么吗？

Answer 1

您的级联位于Employee。这意味着，您需要使用添加的Session session = HibernateUtil.getSessionFactory().openSession(); session.beginTransaction(); Department department = new Department("java"); deparmtment.getEmployees().add(new Employee("Jakab Gipsz",department)); deparmtment.getEmployees().add(new Employee("Captain Nemo",department)); session.save(department); session.getTransaction().commit();实例保存var result: NSArray = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as! NSArray println("result: \(result)")实例。员工将会得救。

        var str = "[{\"person\": {\"name\":\"Dani\",\"age\":\"24\"}},{\"person\": {\"name\":\"ray\",\"age\":\"70\"}}]"

        var data : NSData = str.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!

        var result: NSArray = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableContainers, error: nil) as! NSArray
        println("Response:  \(result)")
        println("Oth Object:  \(result[0])")

Answer 2

保存员工时，部门未保存，因为没有级联。如果需要，您需要在Employee类中添加级联。

@ManyToOne(cascade = CascadeType.save)
private Department department;

Answer 3

这是因为您在字段初始值设定项中创建了Employee，因此如果它没有被托管Employee实例覆盖，Hibernate会将其视为瞬态并在刷新时抛出异常。

解决方案不是在字段初始值设定项中创建它：

@OneToMany(mappedBy="department",cascade=CascadeType.ALL)
private List<Employee> employees;

您还必须关注 James 回答

Session session = HibernateUtil.getSessionFactory().openSession();
session.beginTransaction();

Department department = new Department("java");
deparmtment.getEmployees().add(new Employee("Jakab Gipsz",department));
deparmtment.getEmployees().add(new Employee("Captain Nemo",department));

session.save(department);

session.getTransaction().commit();

即使我设置了cascade = CascadeType.ALL，也会出现TransientObjectException

3 个答案: