Hibernate基于外键的一对多单向关联

程序员文章站 2022-05-23 21:05:42

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一对多，一个分类Category下有多个Product，从Cateogry角度去保存数据。

创建数据库脚本如下：（参看附件）

-- 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=3 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,'fruit','fruit category');
/*!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,
  `name` varchar(30) NOT NULL,
  `price` int(11) NOT NULL,
  `description` varchar(30) NOT NULL,
  `category_id` int(11) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `product_fk` (`category_id`)
) ENGINE=MyISAM 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,'orige',20,'orige',1),(2,'apple',10,'apple',1);
/*!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 2012-08-09 21:40:19

这是一个非常不错的例子，呵呵，至少整个过程大家可以很清楚的明白。。

//Category.java

public class Category implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private String description;
	private Set<Product> products = new HashSet<Product>();

//Product.java

public class Product implements java.io.Serializable {

	// Fields

	private Integer id;
	private String name;
	private Integer price;
	private String description;

//Category.hbm.xml

        <!-- 基于外键的单向一对多关联 -->
        <!-- 单向一对多在一端进行配置 -->
        <!-- set的name代表一端的set属性，table指向多端的关联表-->
        <!-- key的column属性代表外键 -->
        <!-- cascade="save-update" ,使用保存数据的级联操作-->
        <set name="products" table="product" cascade="save-update">
        <key column="category_id"  not-null="true" />
        <one-to-many class="com.v512.examples.Product"/>
        </set>

//HibernateTest.java

//保存数据

	public static void addProduct()
	{
		Product product = new Product();
		product.setDescription("apple");
		product.setName("apple");
		product.setPrice(10);
		
		
		Product product1 = new Product();
		product1.setDescription("orige");
		product1.setName("orige");
		product1.setPrice(20);
		
		Category category = new Category();
		category.setDescription("fruit category");
		category.setName("fruit");
		
		
		Set<Product> products = new HashSet<Product>();
		products.add(product);
		products.add(product1);
		
		category.setProducts(products);
		
		Session session = HibernateUtil.getSessionFactory().openSession();
		Transaction tx = session.beginTransaction();
		session.save(category);
		//启用级联操作
//		session.save(product);
//		session.save(product1);
		tx.commit();
		session.close();
		HibernateUtil.shutdown();
		
	}

输入信息如下：

21:15:48,906 DEBUG JDBCTransaction:87 - current autocommit status: false
21:15:48,906 DEBUG IncrementGenerator:104 - fetching initial value: select max(id) from category
21:15:48,906 DEBUG AbstractBatcher:410 - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
21:15:48,937 DEBUG SQL:111 - 
    select
        max(id) 
    from
        category
Hibernate: 
    select
        max(id) 
    from
        category
21:15:48,953 DEBUG IncrementGenerator:119 - first free id: 1
21:15:48,953 DEBUG AbstractBatcher:418 - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
21:15:48,953 DEBUG AbstractSaveEventListener:135 - generated identifier: 1, using strategy: org.hibernate.id.IncrementGenerator
21:15:48,968 DEBUG IncrementGenerator:104 - fetching initial value: select max(id) from product
21:15:48,968 DEBUG AbstractBatcher:410 - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
21:15:48,968 DEBUG SQL:111 - 
    select
        max(id) 
    from
        product
Hibernate: 
    select
        max(id) 
    from
        product
21:15:48,968 DEBUG IncrementGenerator:119 - first free id: 1
21:15:48,968 DEBUG AbstractBatcher:418 - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
21:15:48,968 DEBUG AbstractSaveEventListener:135 - generated identifier: 1, using strategy: org.hibernate.id.IncrementGenerator
21:15:48,968 DEBUG AbstractSaveEventListener:135 - generated identifier: 2, using strategy: org.hibernate.id.IncrementGenerator
21:15:48,968 DEBUG JDBCTransaction:134 - commit
21:15:48,968 DEBUG AbstractFlushingEventListener:134 - processing flush-time cascades
21:15:48,968 DEBUG AbstractFlushingEventListener:177 - dirty checking collections
21:15:48,968 DEBUG Collections:199 - Collection found: [com.v512.examples.Category.products#1], was: [<unreferenced>] (initialized)
21:15:48,984 DEBUG AbstractFlushingEventListener:108 - Flushed: 3 insertions, 0 updates, 0 deletions to 3 objects
21:15:48,984 DEBUG AbstractFlushingEventListener:114 - Flushed: 1 (re)creations, 0 updates, 0 removals to 1 collections
21:15:48,984 DEBUG Printer:106 - listing entities:
21:15:48,984 DEBUG Printer:113 - com.v512.examples.Product{id=1, price=10, description=apple, name=apple}
21:15:48,984 DEBUG Printer:113 - com.v512.examples.Category{id=1, description=fruit category, name=fruit, products=[com.v512.examples.Product#2, com.v512.examples.Product#1]}
21:15:48,984 DEBUG Printer:113 - com.v512.examples.Product{id=2, price=20, description=orige, name=orige}
21:15:48,984 DEBUG AbstractBatcher:410 - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
21:15:48,984 DEBUG SQL:111 - 
    insert 
    into
        hibernate_demo.category
        (name, description, id) 
    values
        (?, ?, ?)
Hibernate: 
    insert 
    into
        hibernate_demo.category
        (name, description, id) 
    values
        (?, ?, ?)
21:15:48,984 DEBUG AbstractBatcher:66 - Executing batch size: 1
21:15:48,984 DEBUG AbstractBatcher:418 - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
21:15:48,984 DEBUG AbstractBatcher:410 - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
21:15:48,984 DEBUG SQL:111 - 
    insert 
    into
        hibernate_demo.product
        (name, price, description, category_id, id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        hibernate_demo.product
        (name, price, description, category_id, id) 
    values
        (?, ?, ?, ?, ?)
21:15:48,984 DEBUG AbstractBatcher:248 - reusing prepared statement
21:15:48,984 DEBUG SQL:111 - 
    insert 
    into
        hibernate_demo.product
        (name, price, description, category_id, id) 
    values
        (?, ?, ?, ?, ?)
Hibernate: 
    insert 
    into
        hibernate_demo.product
        (name, price, description, category_id, id) 
    values
        (?, ?, ?, ?, ?)
21:15:48,984 DEBUG AbstractBatcher:66 - Executing batch size: 2
21:15:48,984 DEBUG AbstractBatcher:418 - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
21:15:48,984 DEBUG AbstractCollectionPersister:1112 - Inserting collection: [com.v512.examples.Category.products#1]
21:15:48,984 DEBUG AbstractBatcher:410 - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)
21:15:48,984 DEBUG SQL:111 - 
    update
        hibernate_demo.product 
    set
        category_id=? 
    where
        id=?
Hibernate: 
    update
        hibernate_demo.product 
    set
        category_id=? 
    where
        id=?
21:15:48,984 DEBUG AbstractBatcher:248 - reusing prepared statement
21:15:48,984 DEBUG SQL:111 - 
    update
        hibernate_demo.product 
    set
        category_id=? 
    where
        id=?
Hibernate: 
    update
        hibernate_demo.product 
    set
        category_id=? 
    where
        id=?
21:15:48,984 DEBUG AbstractCollectionPersister:1194 - done inserting collection: 2 rows inserted
21:15:48,984 DEBUG AbstractBatcher:66 - Executing batch size: 2
21:15:48,984 DEBUG AbstractBatcher:418 - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)
21:15:48,984 DEBUG JDBCTransaction:147 - committed JDBC Connection
21:15:48,984 DEBUG ConnectionManager:427 - aggressively releasing JDBC connection
21:15:48,984 DEBUG ConnectionManager:464 - releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]
21:15:49,000  INFO SessionFactoryImpl:853 - closing
21:15:49,000  INFO DriverManagerConnectionProvider:170 - cleaning up connection pool: jdbc:mysql://localhost:3306/hibernate_demo

如果我们不使用级联操作，即cascade=“save-update”，则需要先保存category，然后再保存product。

那么保存数据就是这样

		session.save(category);
		//启用级联操作
		session.save(product);
		session.save(product1);
		tx.commit();

而启用级联，则只需要保存category就行。

cascade取值如下：

all : 所有情况下均进行关联操作。
none：所有情况下均不进行关联操作。（默认值）
save-update:在执行save/update/saveOrUpdate时进行关联操作。
delete：在执行delete时进行关联操作。

请注意看一下sql，以Hibernate：开头的才是hibernate执行的sql，其他的代表发送给hibernate执行的sql语句。刚开始看错了，还以为hibernate执行了多条sql。

这种方法Hibernate reference称之为
基于外键关联的单向一对多关联是一种很少见的情况，并不推荐使用。

推荐使用：
基于连接表的单向一对多关联应该优先被采用。请注意，通过指定unique="true"，我们可以把多样性从多对多改变为一对多。

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