java - 为什么关联表无法使用 hibernate 正确更新？

Question

我已经创建了员工和部门实体。这些具有双向多对一和一对多关系。

使用 REST 客户端，我添加部门和员工。

添加部门:

{
  "name":"IT"
}

添加员工:

{"name": "Emp01" ,
 "address": 
    {
     "street" :"Street01" ,
     "city" :"City01" ,
     "state" :"State01" ,
     "country" :"Country01"
    },
 "department":{"id":"1"}
}

现在，我想通过关联现有员工来添加新部门。

{
  "name":"Admin",
  "employees":
  [{
      "id":3
    }]
}

现在，部门已成功添加，但员工表未正确更新。除 id 外，其他字段均被空白。理想情况下，hibernate 应该使用最新的部门 ID 更新员工。请让我知道这里可能缺少什么？谢谢。

Employee.java

package com.empcatalogue.model;

import javax.persistence.CascadeType;
import javax.persistence.Embedded;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;

@Entity
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String name;

    @Embedded
    private Address address;

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

    public String getName() {
        return name;
    }

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

    public int getId() {
        return id;
    }

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

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public Department getDepartment() {
        return department;
    }

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

Department.java

package com.empcatalogue.model;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class Department {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    private String name;

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

    public String getName() {
        return name;
    }

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

    public int getId() {
        return id;
    }

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

    public List<Employee> getEmployees() {
        return employees;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }

}

EmployeeRepository.java

...
...
...    
public void addEmployee(Employee emp) {


    Session session = RepoManager.getSessionFactory().openSession();
        try {
            session.beginTransaction();

            session.save(emp);

            session.getTransaction().commit();
        } catch (Exception e) {
            session.getTransaction().rollback();
        } finally {
            session.close();
        }
    }

DepartmentRepository.java

...
...
...
    public void addDepartment(Department department) {
        Session session = RepoManager.getSessionFactory().openSession();
        try {
            session.beginTransaction();

            session.save(department);

            session.getTransaction().commit();
        } catch (Exception e) {
            session.getTransaction().rollback();
        } finally {
            session.close();
        }

    }

Answer 1

您正在使用 javax.persistence 包进行实现，但您将问题标记为 Hibernate。 Hibernate只是JPA(Java Persistence API)的实现之一。甚至 Hibernate 网页也推荐使用 JPA。除非您维护遗留代码，否则最好使用 JPA API 来持久保存和获取您的实体。

现在回答你的问题:

Now, I want to add a new department by associating an existing employee.

为了能够保留并更新您的实体，您应该遵循以下步骤(代码行只是伪代码):

• 创建 Department 实体的实例:

  Department dept = new Department();
  dept.setName(...);
  

• 在事务中从数据库中获取现有的 Employee 实体:

  Employee emp = session.get(Employee.class, <employee_id_here>);
  

• 将实体实例连接在一起:

  dept.getEmployees().add(emp);
  emp.setDepartment(dept);
  

• 坚持员工:

  session.save(dept);
  

您应该在事务中完成所有这些操作，并且一切都应该按预期进行。