惠州分享Java中的JPA覆盖多对多映射实例_北大青鸟IT学校

Java是现在非常主流的编程语言之一，很多人想转行学习Java。那么下面惠州北大青鸟老师给大家分享Java中的JPA覆盖多对多映射实例，希望对大家的学习有帮助。

实例

以下代码来自Employee.java。

package cn.w3cschool.common;

import java.util.Collection;
import java.util.ArrayList;

import javax.persistence.CollectionTable;
import javax.persistence.Column;
import javax.persistence.ElementCollection;
import javax.persistence.Embedded;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToMany;

@Entitypublic class Employee {
   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)    private int id;

   @Embedded    private EmployeeName name;    private long salary;
   
   @ManyToMany(mappedBy="employeesByName")    private Collection<Department> departments;    public Employee() {
       name = new EmployeeName();
       departments = new ArrayList<Department>();
   }    
   public int getId() {
       return id;
   }    
   public void setId(int id) {
       this.id = id;
   }    
   public EmployeeName getName() {
       return name;
   }    public void setName(EmployeeName name) {
       this.name = name;
   }    public String getFirstName() {
       return name.getFirst_Name();
   }    public void setFirstName(String firstName) {
       this.name.setFirst_Name(firstName);
   }    public String getLastName() {
       return name.getLast_Name();
   }    public void setLastName(String lastName) {
       this.name.setLast_Name(lastName);
   }    public long getSalary() {
       return salary;
   }    public void setSalary(long salary) {
       this.salary = salary;
   }    
   public Collection<Department> getDepartments() {
       return departments;
   }    
   public void setDepartments(Collection<Department> departments) {
       this.departments = departments;
   }    public String toString() {
       StringBuffer aBuffer = new StringBuffer("Employee ");
       aBuffer.append(" id: ");
       aBuffer.append(id);
       aBuffer.append(" name: ");
       aBuffer.append(getLastName());
       aBuffer.append(", ");
       aBuffer.append(getFirstName());
       aBuffer.append(" with deptCount: ");        if(null != departments) {
           aBuffer.append(departments.size());
       }
       return aBuffer.toString();
   }
}

以下代码来自EmployeeName.java。

package cn.w3cschool.common;


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

@Embeddablepublic 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;
   }
}

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;

@Transactionalpublic class PersonDaoImpl {  public void test() {
   Employee e = new Employee();
   e.setFirstName("Tom");
   e.setLastName("Smith");
   Department d = new Department();
 
   d.setName("test");

   EmployeeName name = new EmployeeName();
   name.setFirst_Name("Tom");
   name.setLast_Name("Smith");
   
   e.getDepartments().add(d);
   
   d.getEmployees().put(name, e);
   
   
   em.persist(e);    
   em.persist(d);
 

 }

 @PersistenceContext  private EntityManager em;
}

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.AttributeOverride;
import javax.persistence.AttributeOverrides;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.ManyToMany;


@Entitypublic class Department {
   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)    private int id;    private String name;
   
   @ManyToMany
   @JoinTable(name="DEPT_EMP",
       joinColumns=@JoinColumn(name="DEPT_ID"),
       inverseJoinColumns=@JoinColumn(name="EMP_ID"))
   @AttributeOverrides({
       @AttributeOverride(
           name="first_Name",
           column=@Column(name="EMP_FNAME")),
       @AttributeOverride(
           name="last_Name",
           column=@Column(name="EMP_LNAME"))
   })    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 = employee.getName();
       employeesByName.put(empName, employee);
   }    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();
           }
       }
   }    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: DEPT_EMP
Row:
   Column Name: DEPT_ID,
   Column Type: INTEGER:
   Column Value: 1

   Column Name: EMP_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: Smith





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

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

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

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

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