Hibernate Annotation 基于外键的一对多双向关联

纠结了好久呀，因为没有set，关联关系没有保存对，导致插入数据的时候老是空的，我还以为注解用过了呢。

//sql

-- MySQL dump 10.13  Distrib 5.1.55, for Win32 (ia32)
--
-- Host: localhost    Database: hibernate_demo
-- ------------------------------------------------------
-- Server version	5.1.55-community

/*!40101 SET @OLD_CHARACTER_SET_CLIENT=@@CHARACTER_SET_CLIENT */;
/*!40101 SET @OLD_CHARACTER_SET_RESULTS=@@CHARACTER_SET_RESULTS */;
/*!40101 SET @OLD_COLLATION_CONNECTION=@@COLLATION_CONNECTION */;
/*!40101 SET NAMES utf8 */;
/*!40103 SET @OLD_TIME_ZONE=@@TIME_ZONE */;
/*!40103 SET TIME_ZONE='+00:00' */;
/*!40014 SET @OLD_UNIQUE_CHECKS=@@UNIQUE_CHECKS, UNIQUE_CHECKS=0 */;
/*!40014 SET @OLD_FOREIGN_KEY_CHECKS=@@FOREIGN_KEY_CHECKS, FOREIGN_KEY_CHECKS=0 */;
/*!40101 SET @OLD_SQL_MODE=@@SQL_MODE, SQL_MODE='NO_AUTO_VALUE_ON_ZERO' */;
/*!40111 SET @OLD_SQL_NOTES=@@SQL_NOTES, SQL_NOTES=0 */;

--
-- Table structure for table `category`
--

DROP TABLE IF EXISTS `category`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `category` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(30) NOT NULL,
  `description` varchar(30) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `category`
--

LOCK TABLES `category` WRITE;
/*!40000 ALTER TABLE `category` DISABLE KEYS */;
INSERT INTO `category` VALUES (1,'fruit2','fruit category2'),(2,'fruit2','fruit category2'),(3,'fruit2','fruit category2');
/*!40000 ALTER TABLE `category` ENABLE KEYS */;
UNLOCK TABLES;

--
-- Table structure for table `product`
--

DROP TABLE IF EXISTS `product`;
/*!40101 SET @saved_cs_client     = @@character_set_client */;
/*!40101 SET character_set_client = utf8 */;
CREATE TABLE `product` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(30) NOT NULL,
  `price` int(11) NOT NULL,
  `description` varchar(30) NOT NULL,
  `category_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `category_id` (`category_id`)
) ENGINE=MyISAM AUTO_INCREMENT=9 DEFAULT CHARSET=latin1;
/*!40101 SET character_set_client = @saved_cs_client */;

--
-- Dumping data for table `product`
--

LOCK TABLES `product` WRITE;
/*!40000 ALTER TABLE `product` DISABLE KEYS */;
INSERT INTO `product` VALUES (1,'orige2',20,'orige2',1),(2,'apple2',10,'apple2',1),(3,'orige2',20,'orige2',2),(4,'apple2',10,'apple2',2),(5,'orige2',20,'orige2',3),(6,'apple2',10,'apple2',3);
/*!40000 ALTER TABLE `product` ENABLE KEYS */;
UNLOCK TABLES;
/*!40103 SET TIME_ZONE=@OLD_TIME_ZONE */;

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40101 SET CHARACTER_SET_CLIENT=@OLD_CHARACTER_SET_CLIENT */;
/*!40101 SET CHARACTER_SET_RESULTS=@OLD_CHARACTER_SET_RESULTS */;
/*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

-- Dump completed on 2012-08-22 23:27:56

//Category.java

@Entity
@Table(name="category")
public class Category implements java.io.Serializable {

	// Fields
	private static final long serialVersionUID = 3763960444574701564L;
	
	@Id
	@GenericGenerator(name="incrementGenerator", strategy="increment")
	@GeneratedValue(generator="incrementGenerator", strategy=GenerationType.IDENTITY)
	@Column(name="id")
	private Integer id;
	
	@Column(name="name", nullable=false)
	private String name;
	
	@Column(name="description", nullable=false)
	private String description;

	@OneToMany(targetEntity=Product.class, cascade=CascadeType.ALL, mappedBy="category")
	@JoinColumn(name="category_id")//可有可无，告诉一端category_id是外键
	private Set<Product> products = new HashSet<Product>();

//Product.java

@Entity
@Table(name="product")
public class Product implements java.io.Serializable {

	// Fields
	private static final long serialVersionUID = -7292036796553578847L;
	
	@Id
	@GenericGenerator(name="incrementGenerator", strategy="increment")
	@GeneratedValue(generator="incrementGenerator", strategy=GenerationType.IDENTITY)
	@Column(name="id")
	private Integer id;
	
	@Column(name="name", nullable=false)
	private String name;
	
	@Column(name="price", nullable=false)
	private Integer price;
	
	@Column(name="description",nullable=false)
	private String description;
	
	@ManyToOne(targetEntity=Category.class, cascade=CascadeType.ALL)
	//指出category_id是外键，参考其他表的主键列id
	@JoinColumn(name="category_id", referencedColumnName="id",nullable=false)
	private Category category;

//HibernateTest.java

package com.zyp.examples;

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

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

public class HibernateTest {

	public static void main(String[] args) {
		
		//同时保存分类和产品
		addAll();
		
//		deleteByCategory();
		

	}
	
	public static void deleteByCategory()
	{
		Session session = HibernateUtil.getSessionFactory().openSession();
		Transaction tx = session.beginTransaction();
		Category cat = (Category) session.load(Category.class, new Integer(3));
		session.delete(cat);

		tx.commit();
		session.close();
		HibernateUtil.shutdown();
	}
	
	public static void addAll()
	{
		Category category = new Category();
		category.setDescription("fruit category2");
		category.setName("fruit2");
		
		Product product = new Product();
		product.setDescription("apple2");
		product.setName("apple2");
		product.setPrice(10);
		product.setCategory(category);
		
		
		Product product1 = new Product();
		product1.setDescription("orige2");
		product1.setName("orige2");
		product1.setPrice(20);
		//之前忘记加的关联
		product1.setCategory(category);
		
		Set<Product> products = new HashSet<Product>();
		products.add(product);
		products.add(product1);
		//之前忘记加的关联
		category.setProducts(products);
		
		Session session = HibernateUtil.getSessionFactory().openSession();
		Transaction tx = session.beginTransaction();
		session.save(category);
//		session.save(product1);
//		session.save(product);
		//启用级联操作
//		session.save(product);
//		session.save(product1);
		tx.commit();
		session.close();
		HibernateUtil.shutdown();
		
	}
	
	public static void addCategory()
	{
		Category category = new Category();
		category.setName("fruit");
		category.setDescription("fruit category");
		
		Session session = HibernateUtil.getSessionFactory().openSession();
		Transaction tx = session.beginTransaction();
		session.save(category);
		tx.commit();
		HibernateUtil.shutdown();
	}
	
	
	public static void addProduct()
	{
		Product product = new Product();
		product.setDescription("banana");
		product.setName("banana");
		product.setPrice(10);
		
		Product product1 = new Product();
		product1.setDescription("tom");
		product1.setName("tom");
		product1.setPrice(20);		
		
		Session session = HibernateUtil.getSessionFactory().openSession();
		Transaction tx = session.beginTransaction();
		Category category = (Category)session.load(Category.class, new Integer(1));
		
		Set<Product> products = new HashSet<Product>();
		products.add(product);
		products.add(product1);
		
		category.setProducts(products);
		
		session.save(category);
		//启用级联操作
//		session.save(product);
//		session.save(product1);
		tx.commit();
		session.close();
		HibernateUtil.shutdown();
		
		
	}
}

之前在保存数据的时候没有在product中保存category，导致外键列总是空的。反复弄之后才发现。。晕。

基于外键关联的一对多

在多对一双向关联关系中，几乎总是双向关联中的多端作为主体(owner)端, 而一的这段关联注解为@OneToMany( mappedBy=... )

此时保存数据只需要3条sql（两条max(id)除外），1条插入cateogry, 2条插入product.
也就是说，在一对多关系中，最好有多端来维护关联关系，这样可以减少两条update语句。
我们需要在从表（即多段配置@joinColumn，标志外键关系，而不是在多端配置）

而如果我们把关联关系交给1端来维护，即Category来维护，则我们需要多出两条update语句。
此时，我们的实体类应该这样配置。

对于一对多的双向映射,如果要一对多这一端维护关联关系, 你需要删除mappedBy元素并将多对一这端的 @JoinColumn的insertable和updatable设置为false. 很明显,这种方案不会得到什么明显的优化,而且还会增加一些附加的UPDATE语句.

@Entity
public class Troop {
    @OneToMany
    @JoinColumn(name="troop_fk") //we need to duplicate the physical information
    public Set<Soldier> getSoldiers() {
    ...
}

@Entity
public class Soldier {
    @ManyToOne
    @JoinColumn(name="troop_fk", insertable=false, updatable=false)
    public Troop getTroop() {
    ...
}

Hibernate Annotation 基于外键的一对多双向关联

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