Hibernate性能优化

使用dynamic-insert与dynamic-update

动态的添加与更新

 

      1)<property>元素 insert属性:设置为false,在insert语句中不包含这个字段,表示永远不会被插入,默认true
      2)<property>元素 update属性:设置为false,在update语句中不包含这个字段,表示永远不会被修改,默认true
      3)<class>元素 mutable属性:设置为false就是把所有的<property>元素的update属性设置为了false,说明这个对象不会被更新,默认true
      4)<property>元素 dynamic-insert属性:设置为true,表示insert对象的时候,生成动态的insert语句,如果这个字段的值是null就不会加入到insert语句当中.默认false
      5)<property>元素 dynamic-update属性,设置为true,表示update对象的时候,生成动态的update语句,如果这个字段的值是null就不会被加入到update语句中,默认false
      6)<class>元素 dynamic-insert属性:设置为true,表示把所有的<property>元素的dynamic-insert属性设置为true,默认false
      7)<class>元素 dynamic-update属性:设置为true,表示把所有的<property>元素的dynamic-update属性设置为true,默认false

 

<class name="com.rbh,examples.Testbook" table="TESTBOOK"
	dynamic-insert="true" dynamic-update="true">
</class>
</hibernate-mapping>

 

 

 

延迟加载(Lazy Loading)

Hibernate为了避免在关联查询中所带来的无谓的性能开销，使用了延迟加载技术，就是在真正需要读取数据的时候，才向数据库执行数据库的读取加载操作.

 

1.持久化对象的延迟加载(默认都为true)

<hibernate-mapping>
	<class name="com.rbh.examples.Category" table="CATEGORY" lazy="true">
	</class>
</hibernate-mapping>

 

2.集合对象的延迟加载(默认都为true)

<class name="com.rbh.examples.Category" table="CATEGORY" lazy="true">
	<set name="products" cascade="save-update" inverse="true" lazy="true">
		<key column="category_id" />
		<one-to-many class="com.rbh.examples.Product"/>
	</set>
</class>

 

3.属性的延迟加载(默认为false)还要对持久化的类做曾强处理

<class name="com.rbh.examples.Category" table="CATEGORY" lazy="true">
	<property name="image" type=java.sql.Clob" column="IMAGE" lazy="true">
</class>

 

 

 解决org.hibernate.LazyInitializationException

1.取消延迟加载(忽略)
2.使用Hibernate.initialize()
3.使用Open Session In view 设计模式

 

集合对象的抓取策略(Fetching strategies)

 

查询抓取

<set name="products" cascade="save-update" inverse="true" fetch="select">
		<key column="category_id" />
		<one-to-many class="com.rbh.examples.Product"/>
</set>

 

		// fetch=select ,lazy=true
		Session session = HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
		Transaction tx = session.beginTransaction();
		Category category = (Category) session.load(Category.class, new Integer(1));
		System.out.println(category.getName());

		Iterator<Product> it = category.getProducts().iterator();
		Product p = null;
		while (it.hasNext()) {
			p = it.next();
			System.out.println(p.getName());
		}
		tx.commit();

 使用HQL语句或者Criteria对象重载抓取策略

		// fetch=select ,lazy=true,HQL重载
		Session session = HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
		Transaction tx = session.beginTransaction();

		Query query = session
				.createQuery("select c from Category c inner join fetch c.products where c.id=? ");
		query.setInteger(0, new Integer(1));
		Category category = (Category) query.uniqueResult();

		System.out.println(category.getName());

		Iterator<Product> it = category.getProducts().iterator();
		Product p = null;
		while (it.hasNext()) {
			p = it.next();
			System.out.println(p.getName());
		}

		tx.commit();

 

子查询抓取

<set name="products" cascade="save-update" inverse="true" fetch="subselect">
		<key column="category_id" />
		<one-to-many class="com.rbh.examples.Product"/>
</set>

 

		// fetch=subselect ,lazy=true
		Session session = HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
		Transaction tx = session.beginTransaction();

		List categorys = session.createQuery("from Category").list();
		for (Iterator<Category> it = categorys.iterator(); it.hasNext();) {
			Category category = it.next();
			System.out.println(category.getName());
			for (Iterator<Product> it2 = category.getProducts().iterator(); it2.hasNext();) {
				Product product = it2.next();
				System.out.println(product.getName());
			}
		}
		tx.commit();

连接查询抓取

<set name="products" cascade="save-update" inverse="true" fetch="join">
		<key column="category_id" />
		<one-to-many class="com.rbh.examples.Product"/>
</set>

 

		// fetch=join ,lazy=true
		Session session = HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
		Transaction tx = session.beginTransaction();
		Category category = (Category) session.load(Category.class, new Integer(1));
		System.out.println(category.getName());

		Iterator<Product> it = category.getProducts().iterator();
		Product p = null;
		while (it.hasNext()) {
			p = it.next();
			System.out.println(p.getName());
		}
		tx.commit();

批量抓取

<set name="products" cascade="save-update" inverse="true" batch-size="5">
		<key column="category_id" />
		<one-to-many class="com.rbh.examples.Product"/>
</set>

 

		// fetch=batch ,lazy=true
		Session session = HibernateSessionFactoryUtil.getSessionFactory().getCurrentSession();
		Transaction tx = session.beginTransaction();

		List<Category> categorys = session.createQuery("from Category").list();
		System.out.println(categorys.get(3).getProducts());
		System.out.println(categorys.get(0).getProducts());
		
		tx.commit();