JPA教程 - JPA 嵌入式键映射示例

以下代码显示如何在一对多映射中使用嵌入式键。

例子

下面的代码来自Department.java。

package cn.w3cschool.common;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

import javax.persistence.MapKey;
import javax.persistence.OneToMany;


@Entity
public class Department {
    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;
    private String name;
    
    @OneToMany(mappedBy="department")
    private Map<EmployeeName, Employee> employeesByName;
   
    
    public Department() {
        employeesByName = new HashMap<EmployeeName,Employee>();
    }
        
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String deptName) {
        this.name = deptName;
    }
    
    public Map<EmployeeName, Employee> getEmployees() {
        return employeesByName;
    }

    public void addEmployee(Employee employee) {
        EmployeeName empName = new EmployeeName();
        empName.setFirst_Name(employee.getFirstName());
        empName.setLast_Name(employee.getLastName());
        employeesByName.put(empName, employee);
        if (employee.getDepartment() != null) {
            employee.getDepartment().removeEmployee(employee);
        }
        employee.setDepartment(this);
    }

    public void removeEmployee(Employee employee) {
        Iterator iter = employeesByName.entrySet().iterator();
        while (iter.hasNext()) {
            Employee current = ((Map.Entry<EmployeeName,Employee>) iter.next()).getValue();
            if (current.getId() == employee.getId()) {
                iter.remove();
                current.setDepartment(null);
            }
        }
    }

    public String toString() {
        StringBuffer aBuffer = new StringBuffer("Department ");
        aBuffer.append(" id: ");
        aBuffer.append(id);
        aBuffer.append(" name: ");
        aBuffer.append(name);
        aBuffer.append(" employeeCount: ");
        aBuffer.append(employeesByName.size());
        return aBuffer.toString();
    }
}

以下代码来自Employee.java。

package cn.w3cschool.common;

import javax.persistence.Column;
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.IDENTITY)
    private int id;
    @Column(name="F_NAME")
    private String firstName;
    @Column(name="L_NAME")
    private String lastName;    
    private long salary;
    
    @ManyToOne
    private Department department;

    
    public int getId() {
        return id;
    }
    
    public void setId(int id) {
        this.id = id;
    }
    
    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public long getSalary() {
        return salary;
    }

    public void setSalary(long salary) {
        this.salary = salary;
    }
    
    public Department getDepartment() {
        return department;
    }
    
    public void setDepartment(Department department) {
        this.department = department;
    }


    public String toString() {
        StringBuffer aBuffer = new StringBuffer("Employee ");
        aBuffer.append(" id: ");
        aBuffer.append(id);
        aBuffer.append(" name: ");
        aBuffer.append(lastName);
        aBuffer.append(", ");
        aBuffer.append(firstName);
        aBuffer.append(" with dept: ");
        if(null != department) {
            aBuffer.append(department.getName());
        }
        return aBuffer.toString();
    }
}

下面的代码来自PersonDaoImpl.java。

package cn.w3cschool.common;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.transaction.annotation.Transactional;

@Transactional
public class PersonDaoImpl {
  public void test() {
    Employee e = new Employee();
    e.setFirstName("Tom");

    Department d = new Department();
  
    d.setName("test");
    
    e.setDepartment(d);
    
    EmployeeName name = new EmployeeName();
    name.setFirst_Name("Tom");
    d.getEmployees().put(name, e);
    
    
    em.persist(e);    
    em.persist(d);
   

  }

  @PersistenceContext
  private EntityManager em;
}

以下代码来自EmployeeName.java。

package cn.w3cschool.common;


import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
public class EmployeeName {
    @Column(name="F_NAME", insertable=false, updatable=false)
    private String first_Name;
    @Column(name="L_NAME", insertable=false, updatable=false)
    private String last_Name;
    
    public String getFirst_Name() {
        return first_Name;
    }
    public void setFirst_Name(String firstName) {
        first_Name = firstName;
    }
    public String getLast_Name() {
        return last_Name;
    }
    public void setLast_Name(String lastName) {
        last_Name = lastName;
    }
}

以下是数据库转储。

Table Name: DEPARTMENT
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: NAME,
    Column Type: VARCHAR:
    Column Value: test





Table Name: EMPLOYEE
 Row:
    Column Name: ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: F_NAME,
    Column Type: VARCHAR:
    Column Value: Tom

    Column Name: L_NAME,
    Column Type: VARCHAR:
    Column Value: null

    Column Name: SALARY,
    Column Type: BIGINT:
    Column Value: 0

    Column Name: DEPARTMENT_ID,
    Column Type: INTEGER:
    Column Value: 1