JPA教程 - JPA ElementCollection通用目标实体示例

以下部分显示如何将Java集合映射到数据库。它使用@ElementCollection注释来标记集合中的元素类型。

例子

以下代码来自Employee.java。

package cn.w3cschool.common;

import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Set;

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

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

    // Using a targetClass instead of generics
    @ElementCollection(targetClass=VacationEntry.class)
    private Collection vacationBookings = new LinkedList();

    // Using generics in place of a targetClass
    @ElementCollection
    private Set<String> nickNames = new HashSet();
    
    public Collection getVacationBookings() {
        return vacationBookings;
    }

    public void setVacationBookings(Collection vacationBookings) {
        this.vacationBookings = vacationBookings;
    }

    public Set<String> getNickNames() {
        return nickNames;
    }

    public void setNickNames(Set<String> nickNames) {
        this.nickNames = nickNames;
    }
    
    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 String toString() {
        return "Employee id: " + getId() + " name: " + getName() + 
               " salary: " + getSalary() + 
               " nickNames: " + nickNames;
    }
}

以下代码来自VacationEntry.java。

package cn.w3cschool.common;


import java.util.Calendar;

import javax.persistence.Column;
import javax.persistence.Embeddable;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;

@Embeddable
public class VacationEntry {
    @Temporal(TemporalType.DATE)
    private Calendar startDate;
    @Column(name="DAYS")
    private int daysTaken;

    public VacationEntry() {}

    public VacationEntry(Calendar aStartDate, int daysTakenInt) {
        startDate = aStartDate;
        daysTaken = daysTakenInt;
    }
    
    public Calendar getStartDate() {
        return startDate;
    }
    public void setStartDate(Calendar startDate) {
        this.startDate = startDate;
    }
    public int getDaysTaken() {
        return daysTaken;
    }
    public void setDaysTaken(int daysTaken) {
        this.daysTaken = daysTaken;
    }

    public String toString() {
        return "VacationEntry startDate: " + getStartDate().getTime() + 
               ", daysTaken: " + getDaysTaken();
    }
}

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 emp = new Employee();
    emp.setName("name");
    emp.setSalary(12345);
    
    VacationEntry v = new VacationEntry();
    v.setDaysTaken(10);
    
    emp.getVacationBookings().add(v);
    emp.getNickNames().add("Tester");
    em.persist(emp);
  }

  @PersistenceContext
  private EntityManager em;
}

这里是数据库表转储。

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

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

    Column Name: SALARY,
    Column Type: BIGINT:
    Column Value: 12345


Table Name: EMPLOYEE_NICKNAMES
 Row:
    Column Name: EMPLOYEE_ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: NICKNAMES,
    Column Type: VARCHAR:
    Column Value: Tester





Table Name: EMPLOYEE_VACATIONBOOKINGS
 Row:
    Column Name: EMPLOYEE_ID,
    Column Type: INTEGER:
    Column Value: 1

    Column Name: DAYS,
    Column Type: INTEGER:
    Column Value: 10

    Column Name: STARTDATE,
    Column Type: DATE:
    Column Value: null