Hibernate进阶学习4
深入学习hibernate的查询语句
测试HQL查询
package com.hibernate.test; import com.hibernate.domain.Customer; import com.hibernate.utils.HibernateUtils; import org.hibernate.Query; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import java.util.List; /** * @author: 肖德子裕 * @date: 2018/11/16 10:26 * @description: 测试HQL语句(hibernate独有的面向对象的语法)（适合不复杂的多表查询） */ public class Test1 { /** * 排序查询 */ @Test public void test1(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 String hql="from Customer order by cust_id"; //2）创建查询对象 Query query = session.createQuery(hql); //3）执行查询 List<Customer> list = query.list(); System.out.println(list); /*******************************************************/ tx.commit(); session.close(); } /** * 统计查询 */ @Test public void test2(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 String hql="select count(*) from Customer"; String hql1="select sum(cust_id) from Customer"; String hql2="select avg(cust_id) from Customer"; String hql3="select max(cust_id) from Customer"; String hql4="select min(cust_id) from Customer"; //2）创建查询对象 Query query = session.createQuery(hql2); //3）执行查询 Number number = (Number) query.uniqueResult(); System.out.println(number); /*******************************************************/ tx.commit(); session.close(); } /** * 投影查询 */ @Test public void test3(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 String hql="select new Customer(cust_id,cust_name) from Customer"; //2）创建查询对象 Query query = session.createQuery(hql); //3）执行查询 List<Customer> list = query.list(); System.out.println(list); /*******************************************************/ tx.commit(); session.close(); } }
package com.hibernate.test; import com.hibernate.domain.Customer; import com.hibernate.utils.HibernateUtils; import org.hibernate.Query; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import java.lang.reflect.Array; import java.util.Arrays; import java.util.List; /** * @author: 肖德子裕 * @date: 2018/11/19 14:35 * @description: 测试HQL多表查询(hibernate独有的面向对象的语法)（适合不复杂的多表查询） */ public class Test2 { /** * 内连接 */ @Test public void test1(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 String hql="from Customer c inner join c.linkMens"; //2）创建查询对象 Query query = session.createQuery(hql); //3）执行查询 List<Object[]> list = query.list(); for (Object[] obj:list){ System.out.println(Arrays.toString(obj)); } /*******************************************************/ tx.commit(); session.close(); } /** * 迫切内连接 * 将查询到的关联的对象也封装到查询的对象中 */ @Test public void test2(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 String hql="from Customer c inner join fetch c.linkMens"; //2）创建查询对象 Query query = session.createQuery(hql); //3）执行查询 List<Customer> list = query.list(); System.out.println(list); /*******************************************************/ tx.commit(); session.close(); } /** * 左(右)外连接 */ @Test public void test3(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //1）书写HQL语句 //String hql="from Customer c left join c.linkMens"; String hql="from Customer c right join c.linkMens"; //2）创建查询对象 Query query = session.createQuery(hql); //3）执行查询 List<Object[]> list = query.list(); for (Object[] obj:list){ System.out.println(Arrays.toString(obj)); } /*******************************************************/ tx.commit(); session.close(); } }
测试Criteria查询
package com.hibernate.test; import com.hibernate.domain.Customer; import com.hibernate.utils.HibernateUtils; import org.hibernate.Criteria; import org.hibernate.Query; import org.hibernate.Session; import org.hibernate.Transaction; import org.hibernate.criterion.*; import org.junit.Test; import javax.print.attribute.standard.Destination; import java.util.List; /** * @author: 肖德子裕 * @date: 2018/11/16 10:26 * @description: 测试criteria语句(hibernate独有的无语句的全面向对象的查询语法)（适合单表查询） */ public class Test3 { /** * 排序查询 */ @Test public void test(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ Criteria criteria = session.createCriteria(Customer.class); //criteria.addOrder(Order.asc("cust_id")); criteria.addOrder(Order.desc("cust_id")); List list = criteria.list(); System.out.println(list); /*******************************************************/ tx.commit(); session.close(); } /** * 离线查询 * 就是在不创建session的情况下也能进行数据库操作(比如在service和web层调用) */ @Test public void test1(){ //创建离线对象 DetachedCriteria dc=DetachedCriteria.forClass(Customer.class); dc.add(Restrictions.idEq(3L)); //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ Criteria criteria = dc.getExecutableCriteria(session); List list = criteria.list(); System.out.println(list); /*******************************************************/ tx.commit(); session.close(); } }
测试类级别加载策略
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.hibernate.domain" > <class name="Customer" table="cst_customer" lazy="false" > <id name="cust_id" > <generator class="native"></generator> </id> <property name="cust_name" column="cust_name" ></property> <property name="cust_source" column="cust_source" ></property> <property name="cust_industry" column="cust_industry" ></property> <property name="cust_level" column="cust_level" ></property> <property name="cust_linkman" column="cust_linkman" ></property> <property name="cust_phone" column="cust_phone" ></property> <property name="cust_mobile" column="cust_mobile" ></property> <!-- lazy属性: 决定是否延迟加载 true(默认值): 延迟加载,懒加载 false: 立即加载 extra: 极其懒惰 fetch属性: 决定加载策略.使用什么类型的sql语句加载集合数据 select(默认值): 单表查询加载 join: 使用多表查询加载集合 subselect:使用子查询加载集合 --> <!-- batch-size: 抓取集合的数量为3. 抓取客户的集合时,一次抓取几个客户的联系人集合. --> <set name="linkMens" batch-size="3" > <key column="lkm_cust_id" ></key> <one-to-many class="LinkMan" /> </set> </class> </hibernate-mapping>
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.hibernate.domain" > <class name="LinkMan" table="cst_linkman" > <id name="lkm_id" > <generator class="native"></generator> </id> <property name="lkm_gender" ></property> <property name="lkm_name" ></property> <property name="lkm_phone" ></property> <property name="lkm_email" ></property> <property name="lkm_qq" ></property> <property name="lkm_mobile" ></property> <property name="lkm_memo" ></property> <property name="lkm_position" ></property> <!-- fetch 决定加载的sql语句 select: 使用单表查询 join : 多表查询 lazy 决定加载时机 false: 立即加载 proxy: 由customer的类级别加载策略决定. --> <many-to-one name="customer" column="lkm_cust_id" class="Customer" fetch="join" lazy="proxy" > </many-to-one> </class> </hibernate-mapping>
package com.hibernate.test; import com.hibernate.domain.Customer; import com.hibernate.utils.HibernateUtils; import org.hibernate.*; import org.hibernate.criterion.Projections; import org.hibernate.criterion.Restrictions; import org.junit.Test; import java.lang.reflect.Array; import java.util.Arrays; import java.util.List; /** * @author: 肖德子裕 * @date: 2018/11/16 10:26 * @description: 类级别加载策略 */ public class Test4 { /** * 懒加载|延迟加载 */ @Test public void test(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //立即加载 //Customer customer = session.get(Customer.class, "2L"); //延迟加载:查询时只返回一个代理对象，在使用时，根据关联的session查询数据库返回结果 //为了更好的性能，建议延迟加载；延迟加载貌似只是推迟了查询 Customer customer = session.load(Customer.class, "2L"); System.out.println(customer); /*******************************************************/ tx.commit(); session.close(); } }
测试关联级别加载策略
package com.hibernate.test; import com.hibernate.domain.Customer; import com.hibernate.domain.LinkMan; import com.hibernate.utils.HibernateUtils; import org.hibernate.Session; import org.hibernate.Transaction; import org.junit.Test; import java.util.Set; /** * @author: 肖德子裕 * @date: 2018/11/16 10:26 * @description: 关联级别加载策略 */ public class Test5 { /** * lazy与fetch的使用 */ @Test public void test(){ //创建Session对象 Session session = HibernateUtils.openSession(); //开启事务并获取事务对象 Transaction tx = session.beginTransaction(); /********************* 数据库操作 **********************/ //立即加载 Customer customer = session.get(Customer.class, "2L"); Set<LinkMan> linkMens = customer.getLinkMens(); System.out.println(linkMens.size()); System.out.println(linkMens); /*******************************************************/ tx.commit(); session.close(); } }