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QBC检索

QBC（Query By Criteria）是Hibernate提供的另一种检索对象的方式，它主要由Criteria接口、Criterion接口和Expression类组成。

Criteria接口是Hibernate API中的一个查询接口，它需要由session进行创建。一个单独的查询就是Criterion接口的一个实例，用于限制Criteria对象的擦查询，在Hibernate中Criterion对象的创建通常是通过Restrictions工厂类完成的，它提供了条件查询方法。

Criterion是Criteria的查询条件，在Criteria中提供了add（Criterion criterion）方法来添加查询条件。

使用QBC检索对象的实例代码，如下所示

//创建criteria对象	Criteria criteria = session.createCriteria(Customer.class);	//设定查询条件	Criterion criterion = Restrictions.eq("id",1);	//添加查询条件	criteria.add(criterion);	//执行查询，返回查询结果	List
   
     cs = criteria.list();
   

上述代码中查询的是id为1的Customer对象。

QBC检索是使用Restricions对象编写查询条件的，在Restrictions类中提供了大量的静态方法来创建查询条件。

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准备工作

创建一个Customer类:

package pers.zhang.domain;public class Customer {
   	private Long cust_id;	private String cust_name;	private String cust_source;	private String cust_industry;	private String cust_level;	private String cust_linkman;	private String cust_phone;	private String cust_mobile;		public Long getCust_id() {
   		return cust_id;	}	public void setCust_id(Long cust_id) {
   		this.cust_id = cust_id;	}	public String getCust_name() {
   		return cust_name;	}	public void setCust_name(String cust_name) {
   		this.cust_name = cust_name;	}	public String getCust_source() {
   		return cust_source;	}	public void setCust_source(String cust_source) {
   		this.cust_source = cust_source;	}	public String getCust_industry() {
   		return cust_industry;	}	public void setCust_industry(String cust_industry) {
   		this.cust_industry = cust_industry;	}	public String getCust_level() {
   		return cust_level;	}	public void setCust_level(String cust_level) {
   		this.cust_level = cust_level;	}	public String getCust_linkman() {
   		return cust_linkman;	}	public void setCust_linkman(String cust_linkman) {
   		this.cust_linkman = cust_linkman;	}	public String getCust_phone() {
   		return cust_phone;	}	public void setCust_phone(String cust_phone) {
   		this.cust_phone = cust_phone;	}	public String getCust_mobile() {
   		return cust_mobile;	}	public void setCust_mobile(String cust_mobile) {
   		this.cust_mobile = cust_mobile;	}	@Override	public String toString() {
   		return "Customer [cust_id=" + cust_id + ", cust_name=" + cust_name + "]";	}}

配置ORM元数据：

向表中插入数据：

基本查询–查询所有

@Test	//基本查询	public void fun1(){
   			Session session = HibernateUtils.openSession();		Transaction tx = session.beginTransaction();		//-------------------------------------------		//查询所有的Customer对象		Criteria criteria = session.createCriteria(Customer.class);			List
   
     list = criteria.list();		System.out.println(list);		//-------------------------------------------		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        this_.cust_id as cust_id1_0_0_,        this_.cust_name as cust_nam2_0_0_,        this_.cust_source as cust_sou3_0_0_,        this_.cust_industry as cust_ind4_0_0_,        this_.cust_level as cust_lev5_0_0_,        this_.cust_linkman as cust_lin6_0_0_,        this_.cust_phone as cust_pho7_0_0_,        this_.cust_mobile as cust_mob8_0_0_     from        cst_customer this_[Customer [cust_id=1, cust_name=Google], Customer [cust_id=2, cust_name=联想], Customer [cust_id=3, cust_name=百度], Customer [cust_id=4, cust_name=阿里巴巴], Customer [cust_id=5, cust_name=腾讯]]

条件查询

条件查询需要调用criteria.add()方法，参数为Restricions对象。

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@Test	//条件查询	// > 				gt	// >=				ge	// <				lt	// <=				le	// ==				eq	// !=				ne	// in				in	// between and		between	// like 			like	// is not null 		isNotNull	// is null			isNull	// or				or	// and				and	public void fun2(){
   		Session session = HibernateUtils.openSession();		Transaction tx = session.beginTransaction();		//-------------------------------------------		//创建criteria查询对象		Criteria criteria = session.createCriteria(Customer.class);		//添加查询参数 => 查询cust_id为1的Customer对象		criteria.add(Restrictions.eq("cust_id", 1l));		//执行查询获得结果		Customer c = (Customer) criteria.uniqueResult();		System.out.println(c);		//-------------------------------------------		tx.commit();		session.close();	}

运行JUnit测试输出：

Hibernate:     select        this_.cust_id as cust_id1_0_0_,        this_.cust_name as cust_nam2_0_0_,        this_.cust_source as cust_sou3_0_0_,        this_.cust_industry as cust_ind4_0_0_,        this_.cust_level as cust_lev5_0_0_,        this_.cust_linkman as cust_lin6_0_0_,        this_.cust_phone as cust_pho7_0_0_,        this_.cust_mobile as cust_mob8_0_0_     from        cst_customer this_     where        this_.cust_id=?Customer [cust_id=1, cust_name=Google]

分页查询

QBC的分页查询与MySql的limit十分相似，使用两个方法：

1.criteria.setFirstResult(arg)，设置第一条结果从哪个索引开始，相当于limit中的第一个?。 2.criteria.setMaxResults(arg)，设置一次查询多少条数据，相遇于limit中的第二个？。

@Test	//分页查询	public void fun3(){
   		Session session = HibernateUtils.openSession();		Transaction tx = session.beginTransaction();		//-------------------------------------------		Criteria criteria = session.createCriteria(Customer.class);		//设置分页信息 limit ?,?  从第1条开始查，查询2条数据		criteria.setFirstResult(1);		criteria.setMaxResults(2);		List
   
     list = criteria.list();		System.out.println(list);		//-------------------------------------------		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        this_.cust_id as cust_id1_0_0_,        this_.cust_name as cust_nam2_0_0_,        this_.cust_source as cust_sou3_0_0_,        this_.cust_industry as cust_ind4_0_0_,        this_.cust_level as cust_lev5_0_0_,        this_.cust_linkman as cust_lin6_0_0_,        this_.cust_phone as cust_pho7_0_0_,        this_.cust_mobile as cust_mob8_0_0_     from        cst_customer this_ limit ?,        ?[Customer [cust_id=2, cust_name=联想], Customer [cust_id=3, cust_name=百度]]

排序查询

条件查询需要调用criteria.addOrder()方法，参数为Order对象。

Order类的常用方法：作为查询容器的参数

方法名称	描述	使用
Order.asc	升序	Order.asc(String propertyName)
Order.desc	降序	Order.desc(String propertyName)

@Test	public void fun4() {
   		Session session = HibernateUtils.openSession();		Transaction tx = session.beginTransaction();		//-------------------------------------------		Criteria criteria = session.createCriteria(Customer.class);		//设置排序规则 按id降序排序		criteria.addOrder(Order.desc("cust_id"));		//执行查询		List
   
     list = criteria.list();		System.out.println(list);			//-------------------------------------------		tx.commit();		session.close();	}
   

运行JUnit测试输出：

Hibernate:     select        this_.cust_id as cust_id1_0_0_,        this_.cust_name as cust_nam2_0_0_,        this_.cust_source as cust_sou3_0_0_,        this_.cust_industry as cust_ind4_0_0_,        this_.cust_level as cust_lev5_0_0_,        this_.cust_linkman as cust_lin6_0_0_,        this_.cust_phone as cust_pho7_0_0_,        this_.cust_mobile as cust_mob8_0_0_     from        cst_customer this_     order by        this_.cust_id desc[Customer [cust_id=5, cust_name=腾讯], Customer [cust_id=4, cust_name=阿里巴巴], Customer [cust_id=3, cust_name=百度], Customer [cust_id=2, cust_name=联想], Customer [cust_id=1, cust_name=Google]]

统计查询

条件查询需要调用criteria.setProjection()方法，参数为Projection对象。

Projections类的常用方法：作为查询容器的参数:

方法名称	描述	使用
Projections.avg	求平均值	Projections.avg(String propertyName)
Projections.count	统计某属性的数量	Projections.count(String propertyName)
Projections.countDistinct	统计某属性不同值的数量	Projections.countDistinct(String propertyName)
Projections.groupProperty	指定某个属性为分组属性	Projections.groupProperty(String propertyName)
Projections.max	求最大值	Projections.max(String propertyName)
Projections.min	求最小值	Projections.min(String propertyName)
Projections.projectionList	创建一个ProjectionList对象	Projections.projectionList()
Projections.rowCount	统计结果集中的记录条数	Projections.rowCount()
Projections.sum	求某属性的合计	Projections.sum(String propertyName)

@Test	//查询总记录数	public void fun5(){
   		Session session = HibernateUtils.openSession();		Transaction tx = session.beginTransaction();		//-------------------------------------------		//创建criteria查询对象		Criteria criteria = session.createCriteria(Customer.class);		//设置查询的聚合函数 => 总行数		criteria.setProjection(Projections.rowCount());		Long count = (Long) criteria.uniqueResult();		System.out.println(count);		//-------------------------------------------		tx.commit();		session.close();	}

运行JUnit测试输出：

Hibernate:     select        count(*) as y0_     from        cst_customer this_5

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