hibernate中HQL查询详细解析（珍藏版）

    本例模仿部门与员工之间来进行HQL的各种查询，一共有两张表，一张部门表，一张员工表，下面是具体查询代码：

1.Junit测试

package cn.itcast.a_query;import org.hibernate.Query;import org.hibernate.SessionFactory;import org.hibernate.cfg.Configuration;import org.hibernate.classic.Session;import org.junit.Test;public class App_hql {private static SessionFactory sf;static{sf=new Configuration().configure().addClass(Dept.class).addClass(Employee.class).buildSessionFactory();}@Testpublic void all() throws Exception{Session session=sf.openSession();session.beginTransaction();//1.主键查询及区别//Dept dept=(Dept) session.get(Dept.class, 3);//1.对象导航查询/*Dept dept=(Dept) session.get(Dept.class, 3);System.out.println(dept.getDeptName());System.out.println(dept.getEmps());*///HQL查询//注意：使用HQL查询的时候auto-import="true"，要设置true，    //  如果是false，写hql的时候，要指定类的全名/*Query q=session.createQuery("from Dept");System.out.println(q.list());*///a.查询全部列//Query q = session.createQuery("from Dept");  //OK//Query q = session.createQuery("select * from Dept");  //NOK, 错误，不支持*//Query q = session.createQuery("select d from Dept d");  // OK//System.out.println(q.list());// b. 查询指定的列  【返回对象数据Object[] 】//Query q = session.createQuery("select d.deptId,d.deptName from Dept d");  //System.out.println(q.list());// c. 查询指定的列, 自动封装为对象  【必须要提供带参数构造器】//Query q = session.createQuery("select new Dept(d.deptId,d.deptName) from Dept d");  //System.out.println(q.list());// d. 条件查询: 一个条件/多个条件and or/between and/模糊查询// 条件查询： 占位符//Query q=session.createQuery("from Dept d where deptName=?");//q.setString(0,"人事部");//q.setParameter(0,"人事部");//System.out.println(q.list());// 条件查询： 命名参数/*Query q=session.createQuery("from Dept d where deptId=:myid or deptName=:name");q.setParameter("myid", 3);q.setParameter("name", "人事部");System.out.println(q.list());*/// 范围//Query q = session.createQuery("from Dept d where deptId between ? and ?");//q.setParameter(0, 1);//q.setParameter(1, 20);//System.out.println(q.list());// 模糊//Query q = session.createQuery("from Dept d where deptName like ?");//q.setString(0, "%部%");//System.out.println(q.list());// e. 聚合函数统计//Query q = session.createQuery("select count(*) from Dept");//Long num = (Long) q.uniqueResult();//System.out.println(num);// f. 分组查询//-- 统计t_employee表中，每个部门的人数//数据库写法：SELECT dept_id,COUNT(*) FROM t_employee GROUP BY dept_id;// HQL写法//Query q = session.createQuery("select e.dept, count(*) from Employee e group by e.dept");//System.out.println(q.list());session.getTransaction().commit();session.close();}//连接查询@Testpublic void join() throws Exception{Session session=sf.openSession();session.beginTransaction();//1) 内连接   【映射已经配置好了关系，关联的时候，直接写对象的属性即可】    /* Query q = session.createQuery("from Dept d inner join d.emps");     System.out.println(q.list());*///2) 左外连接//Query q = session.createQuery("from Dept d left join d.emps");//3) 右外连接/*Query q = session.createQuery("from Employee e right join e.dept");q.list();*/session.getTransaction().commit();session.close();}// g. 连接查询 - 迫切连接@Testpublic void fetch() throws Exception{Session session = sf.openSession();session.beginTransaction();//1) 迫切内连接    【使用fetch, 会把右表的数据，填充到左表对象中！】/*Query q=session.createQuery("from Dept d inner join fetch d.emps");q.list();*///2) 迫切左外连接/*Query q = session.createQuery("from Dept d left join fetch d.emps");q.list();*/session.getTransaction().commit();session.close();}// HQL查询优化@Testpublic void hql_other(){Session session = sf.openSession();session.beginTransaction();// HQL写死//Query q = session.createQuery("from Dept d where deptId < 10 ");// HQL 放到映射文件中Query q = session.getNamedQuery("getAllDept");q.setParameter(0, 10);System.out.println(q.list());session.getTransaction().commit();session.close();}}

2.Dept.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN""http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="cn.itcast.a_query" auto-import="true"><class name="Dept" table="t_dept" ><id name="deptId"><generator class="native"></generator></id><property name="deptName" length="20"></property><!-- 集合属性，默认使用懒加载 lazytrue 懒加载extra 懒加载(智能)false 关闭懒加载--> <set name="emps" lazy="extra">  <key column="dept_id"></key>  <one-to-many class="Employee"/> </set> <!-- 存放sql语句 --><query name="getAllDept"><![CDATA[from Dept d where deptId < ?]]></query> </class></hibernate-mapping>

3.Dept

package cn.itcast.a_query;import java.util.HashSet;import java.util.Set;public class Dept {private int deptId;private String deptName;public Dept() {super();}public Dept(int deptId, String deptName, Set<Employee> emps) {super();this.deptId = deptId;this.deptName = deptName;this.emps = emps;}public Dept(int deptId, String deptName) {super();this.deptId = deptId;this.deptName = deptName;}// 【一对多】 部门对应的多个员工private Set<Employee> emps = new HashSet<Employee>();public int getDeptId() {return deptId;}public void setDeptId(int deptId) {this.deptId = deptId;}public String getDeptName() {return deptName;}public void setDeptName(String deptName) {this.deptName = deptName;}public Set<Employee> getEmps() {return emps;}public void setEmps(Set<Employee> emps) {this.emps = emps;}}

    其他的配置文件比较简单，这里没有列出来，主要是收藏hibernate的HQL查询语句，以及以后怎样使用HQL来查询