hibernate 映射 set 值對象 簡單映射

 hibernate 映射 set 值對象 簡單映射

應用場景：

     兩個對象間是一對多的關係，且多的一方是值對象，一的一方是實體對象（什麼是值對象什麼是實體對象，請參見本博客的《hibernate 誤區1 正確區分值對象和實體對象》），這時候不能使用組件映射，因爲組件映射通常暗示着一對一的關聯如（本博客的《hibernate 映射 組件映射》中舉得例子一樣，一個人通常只有或者我們的應用系統通常只關注一個家庭地址，一個人也只有一個賬單地址），這時候就要使用set的值對象映射

示例實體：

   User 對一個user，可以在一生中有多份工作，我們的User實體需要保存這些工作的名稱（其他的暫不關注），根據set的語義：不同的 無序的集合。（如果你需要關注順序，請參見本博客的其他文章）我們定義實體如下：

注：如果我們允許用戶不停的添加同一工作到user中的話請參見下篇文章《hibernate 映射 bag/idbag值對象 簡單映射》；

一、XML實現

package com.ccay.test.valueCollection.set;

import java.util.HashSet;
import java.util.Set;

public class User {
	private long userId;
	private String firstname;
	private String lastname;
	private Set<String> tasks = new HashSet<String>();
	public long getUserId() {
		return userId;
	}
	public void setUserId(long userId) {
		this.userId = userId;
	}
	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 Set<String> getTasks() {
		return tasks;
	}
	public void setTasks(Set<String> tasks) {
		this.tasks = tasks;
	}

	
}

HBM.XML文件如下：

 

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.ccay.test.valueCollection.set.User" table="VAL_COLLECTION_SIMPLE_SET_USER" >
        <id name="userId" type="long">
            <column name="USER_ID"/>
            <generator class="native" />
        </id>
        <property name="firstname" type="string">
            <column name="FIRSTNAME" length="40" />
        </property>
        <property name="lastname" type="string">
            <column name="LASTNAME" length="50" />
        </property>
        <set name="tasks" table="VAL_COLLECTION_SIMPLE_SET_TASKS">
        	<key column="USER_ID"/>
        	<element type="string" column="TASKS" not-null="true"/>
        </set>
    </class>
</hibernate-mapping>

測試代碼如下：

package com.ccay.test.valueCollection.set;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.ccay.test.HibernateSessionFactory;

public class Test {
	@org.junit.Test
	public void testDDL(){
		Session session = HibernateSessionFactory.getSession();
		Transaction transaction = session.beginTransaction();
		Set<String> tasks = new HashSet<String>();
		tasks.add("student");
		tasks.add("programer");

		
		User user= new User();
		user.setFirstname("firstName");
		user.setLastname("lastName");
		user.setTasks(tasks);
		
		session.save(user);
		transaction.commit();
		HibernateSessionFactory.closeSession();
	}
}

hibernate自動的schema如下

create table VAL_COLLECTION_SIMPLE_SET_TASKS (
        USER_ID bigint not null,
        TASKS varchar(255) not null,
        primary key (USER_ID, TASKS)
    )
create table VAL_COLLECTION_SIMPLE_SET_USER (
        USER_ID bigint not null auto_increment,
        FIRSTNAME varchar(40),
        LASTNAME varchar(50),
        primary key (USER_ID)
    )
 alter table VAL_COLLECTION_SIMPLE_SET_TASKS 
  add index FK839C9A27309B6B8 (USER_ID), 
  add constraint FK839C9A27309B6B8 
  foreign key (USER_ID) 
  references VAL_COLLECTION_SIMPLE_SET_USER (USER_ID)

註解實現

package com.ccay.test.valueCollection.set.annotation;

import java.util.HashSet;
import java.util.Set;

import javax.persistence.Column;
import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.JoinTable;
import javax.persistence.Table;

import org.hibernate.annotations.CollectionOfElements;
@Entity
@Table(name="VAL_COLLECTION_SIMPLE_SET_USER")
public class User {
	@Id
	@GeneratedValue
	private long userId;
	@Column(name="FIRSTNAME",nullable=false)
	private String firstname;
	@Column(name="LASTNAME",nullable=false)
	private String lastname;
	//已經廢棄的註解
	//@CollectionOfElements(targetElement=java.lang.String.class)
	@ElementCollection(targetClass=java.lang.String.class)
	@JoinTable(
			name="VAL_COLLECTION_SIMPLE_SET_TASKS",
			joinColumns = {@JoinColumn(name="USER_ID")}
			)
	@Column(name="TASKS",nullable=false)
	private Set<String> tasks = new HashSet<String>();
	public long getUserId() {
		return userId;
	}
	public void setUserId(long userId) {
		this.userId = userId;
	}
	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 Set<String> getTasks() {
		return tasks;
	}
	public void setTasks(Set<String> tasks) {
		this.tasks = tasks;
	}
}

測試代碼

package com.ccay.test.valueCollection.set.annotation;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.Transaction;

import com.ccay.test.HibernateSessionFactory;

public class Test {
	@org.junit.Test
	public void testDDL(){
		Session session = HibernateSessionFactory.getSession();
		Transaction transaction = session.beginTransaction();
		Set<String> tasks = new HashSet<String>();
		tasks.add("student");
		tasks.add("programer");

		
		User user= new User();
		user.setFirstname("firstName");
		user.setLastname("lastName");
		user.setTasks(tasks);
		
		session.save(user);
		transaction.commit();
		HibernateSessionFactory.closeSession();
	}
}

自動ddl

    create table VAL_COLLECTION_SIMPLE_SET_TASKS (
        USER_ID bigint not null,
        TASKS varchar(255) not null,
        primary key (USER_ID, TASKS)
    )
    create table VAL_COLLECTION_SIMPLE_SET_USER (
        userId bigint not null auto_increment,
        FIRSTNAME varchar(255) not null,
        LASTNAME varchar(255) not null,
        primary key (userId)
    )
    alter table VAL_COLLECTION_SIMPLE_SET_TASKS 
        add index FK839C9A2794AB95DB (USER_ID), 
        add constraint FK839C9A2794AB95DB 
        foreign key (USER_ID) 
        references VAL_COLLECTION_SIMPLE_SET_USER (userId)

逆向工程