惠州Java中的JPA一对多非类型化映射是什么？_北大青鸟IT学校

Java中的JPA一对多非类型化映射是什么？这是大家在学习Java的过程都会遇到的问题，那么下面我们一起来看看惠州北大青鸟学术部老师是怎么讲解这道题的。

以下代码表示非类型的java.util.Map的目标实体类。

@OneToMany(targetEntity=Employee.class, mappedBy="department")
@MapKeyprivate Map employees;

实例

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.setName("Tom");
   Department d = new Department();
 
   d.setName("test");
   d.getEmployees().put(e, e.getId());
   
   
   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.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;

@Entitypublic class Department {
   @Id @GeneratedValue(strategy=GenerationType.IDENTITY)    private int id;    private String name;
   
   @OneToMany(targetEntity=Employee.class, mappedBy="department")
   @MapKey    private Map employees;    
   public Department() {
       employees = new HashMap();
   }    
   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 void addEmployee(Employee employee) {
       employees.put(employee.getId(), employee);        if (employee.getDepartment() != null) {
           employee.getDepartment().getEmployees().remove(employee.getId());
       }
       employee.setDepartment(this);
   }    
   public Map getEmployees() {
       return employees;
   }    public String toString() {
       StringBuffer aBuffer = new StringBuffer("Department ");
       aBuffer.append(" id: ");
       aBuffer.append(id);
       aBuffer.append(" name: ");
       aBuffer.append(name);
       aBuffer.append(" employeeCount: ");        if(null != employees) {          
           aBuffer.append(employees.size());
       }
       return aBuffer.toString();
   }
}

以下代码来自Employee.java。

package cn.w3cschool.common;

import java.util.Map;
import java.util.Set;

import javax.persistence.CollectionTable;
import javax.persistence.Column;
import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.ManyToOne;
import javax.persistence.MapKeyClass;
import javax.persistence.MapKeyColumn;

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

   @ElementCollection(targetClass=String.class)
   @CollectionTable(name="EMP_PHONE")
   @MapKeyColumn(name="PHONE_TYPE")
   @MapKeyClass(String.class)
   @Column(name="PHONE_NUM")    private Map phoneNumbers;
           
   @ManyToOne    private Department department;    
   public int getId() {
       return id;
   }    
   public void setId(int id) {
       this.id = id;
   }    
   public String getName() {
       return name;
   }    
   public void setName(String name) {
       this.name = name;
   }    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 Map getPhoneNumbers() {
       return phoneNumbers;
   }    public void setPhoneNumbers(Map phoneNumbers) {
       this.phoneNumbers = phoneNumbers;
   }    public String toString() {
       StringBuffer aBuffer = new StringBuffer("Employee ");
       aBuffer.append(" id: ");
       aBuffer.append(id);
       aBuffer.append(" with dept: ");        if(null != department) {
           aBuffer.append(department.getName());
       }
       aBuffer.append(" phoneNumbers: ");        for (Map.Entry e : (Set<Map.Entry>)phoneNumbers.entrySet()) {
           aBuffer.append(e.getKey() + "[" + e.getValue() + "] ");
       }        
       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: EMPLOYEE
Row:
   Column Name: ID,
   Column Type: INTEGER:
   Column Value: 1

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

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

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





Table Name: EMP_PHONE

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