<class name="com.bjsxt.hibernate.Node" table="t_node">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<property name="level"/>
<property name="leaf"/>
<many-to-one name="parent" column="pid"/>
<set name="children" lazy="extra" inverse="true">
<key column="pid"/>
<one-to-many class="com.bjsxt.hibernate.Node"/>
</set>
</class>
Hibernate查询
标准化对象查询:Criteria Query
Hibernate语言查询:HQL
以类和属性来代替表和数据列
支持多态
支持各种关联
减少了SQL的冗余
连接,笛卡尔级,投影,聚合,分组,排序,子查询,SQL函数
from User user where user.group.name=’admin’表连接
等同:
select user.userid form user, group where group.groupname and user.groupid = group.group.id
hibernate查询语言hql
在hql中关键字不区分大小写,但是属性和类名区分大小写
1、简单属性查询【重要】
* 单一属性查询,返回结果集属性列表,元素类型和实体类中相应的属性类型一致
//返回结果集属性列表,元素类型和实体类中相应的属性类型一致
List students = session.createQuery("select name from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
String name = (String)iter.next();
System.out.println(name);
}
* 多个属性查询,返回的集合元素是对象数组,数组元素的类型和对应的属性在实体类中的类型一致
//查询多个属性,其集合元素是对象数组
//数组元素的类型和对应的属性在实体类中的类型一致
//数组的长度取决与select中属性的个数
List students = session.createQuery("select id, name from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
数组的长度取决与select中属性的个数
l 如果认为返回数组不够对象化,可以采用hql动态实例化Student对象
//如果认为返回数组不够对象化,可以采用hql动态实例化Student对象
//此时list中为Student对象集合
List students = session.createQuery("select new Student(id, name) from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getId() + "," + student.getName());
}
主意:实体类要有Student(String id, String name)这样的构造函数
//可以使用别名
List students = session.createQuery("select s.id, s.name from Student s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//可以使用as命名别名
List students = session.createQuery("select s.id, s.name from Student as s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
2、实体对象查询【重要】
* N + 1问题,在默认情况下,使用query.iterate查询,有可以能出现N+1问题
所谓的N+1是在查询的时候发出了N+1条sql语句
1: 首先发出一条查询对象id列表的sql
N: 根据id列表到缓存中查询,如果缓存中不存在与之匹配的数据,那么会根据id发出相应的sql语句
* list和iterate的区别?
* list每次都会发出sql语句,list会向缓存中放入数据,而不利用缓存中的数据
* iterate:在默认情况下iterate利用缓存数据,但如果缓存中不存在数据有可以能出现N+1问题
//返回Student对象的集合
//可以忽略select
List students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
//返回Student对象的集合
//可以忽略select,表可以使用别名
List students = session.createQuery("from Student s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
//返回Student对象的集合
//可以忽略select,表可以使用as命名别名
List students = session.createQuery("from Student as s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
//返回Student对象的集合
//使用select查询实体对象,必须采用别名
List students = session.createQuery("select s from Student as s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
//不支持select * from .....这样的查询语句
List students = session.createQuery("select * from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
/**
* 采用list查询发出一条查询语句,取得Student对象数据、
*
* Hibernate: select student0_.id as id1_, student0_.name as name1_,
* student0_.createTime as createTime1_, student0_.classesid as classesid1_
* from t_student student0_
*
*/
List students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
/**
* 出现N+1问题
*
* 1:发出查询id列表的sql
* Hibernate: select student0_.id as col_0_0_ from t_student student0_
*
* N:在依次发出根据id查询Student对象的sql
* Hibernate: select student0_.id as id1_0_, student0_.name as name1_0_,
* student0_.createTime as createTime1_0_, student0_.classesid as classesid1_0_
* from t_student student0_ where student0_.id=?
*
*/
Iterator iter = session.createQuery("from Student").iterate();
while(iter.hasNext()) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
List students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
System.out.println("---------------------------------------------");
/**
* 不会出现N+1问题
*
* 因为list操作已经将Student对象放到了一级缓存中,所以再次使用iterate操作的时候
* 它首先发出一条查询id列表的sql,在根据id到缓存中去数据,只有在缓存中找不到相应的
* 数据时,才会发出sql到数据库中查询
*
*/
Iterator iter = session.createQuery("from Student").iterate();
while(iter.hasNext()) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
List students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
System.out.println("---------------------------------------------");
/**
* 再次发出查询sql
*
* 在默认情况下list每次都会向数据库发出查询对象的sql,除非配置查询缓存,所以下面的list操作
* 虽然在一级缓存中已经有了对象数据,但list默认情况下不会利用缓存,而再次发出sql
*
* 默认情况下,list会向缓存中放入数据,但不会利用数据
*
*/
students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
3、条件查询【重要】
* 可以采用拼字符串的方式传递参数
* 可以采用 ?来传递参数(索引从0开始)
* 可以采用 :参数名 来传递参数
* 如果传递多个参数,可以采用setParamterList方法
* 在hql中可以使用数据库的函数,如:date_format
//可以拼字符串
List students = session.createQuery("select s.id, s.name from Student s where s.name like '%1%'").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//可以使用?方式传递参数
//参数的索引从0开始
//传递的参数值,不用单引号引起来
//注意方法链编程
List students = session.createQuery("select s.id, s.name from Student s where s.name like ?")
.setParameter(0, "%1%")
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//使用 :参数名称 的方式传递参数值
List students = session.createQuery("select s.id, s.name from Student s where s.name like :myname")
.setParameter("myname", "%1%")
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//使用 :参数名称 的方式传递参数值
List students = session.createQuery("select s.id, s.name from Student s where s.name like :myname and s.id=:myid")
.setParameter("myname", "%1%")
.setParameter("myid", 12)
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//支持in,需要使用setParameterList进行参数传递
List students = session.createQuery("select s.id, s.name from Student s where s.id in(:myids)")
.setParameterList("myids", new Object[]{1, 2, 3, 4, 5})
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//查询2008年2月创建的学生
List students = session.createQuery("select s.id, s.name from Student s where date_format(s.createTime, '%Y-%m')=?")
.setParameter(0, "2008-02")
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
//查询2008-01-10到2008-02-15创建的学生
List students = session.createQuery("select s.id, s.name from Student s where s.createTime between ? and ?")
.setParameter(0, sdf.parse("2008-01-10 00:00:00"))
.setParameter(1, sdf.parse("2008-02-15 23:59:59"))
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
4、hibernate也支持直接使用sql进行查询
List students = session.createSQLQuery("select * from t_student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
5、外置命名查询
* 在映射文件中采用<query>标签来定义hql
* 在程序中采用session.getNamedQuery()方法得到hql查询串
List students = session.getNamedQuery("searchStudents")
.setParameter(0, 10)
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
<query name="searchStudents">
<![CDATA[
SELECT s FROM Student s where s.id<?
]]>
</query>
6、查询过滤器
* 在映射文件中定义过滤器参数
* 在类的映射中使用这些参数
* 在程序中启用过滤器
session.enableFilter("filtertest")
.setParameter("myid", 10);
List students = session.createQuery("from Student").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
<filter-def name="filtertest">
<filter-param name="myid" type="integer"/>
</filter-def>
<class name="com.bjsxt.hibernate.Student" table="t_student">
<id name="id">
<generator class="native"/>
</id>
<property name="name"/>
<property name="createTime"/>
<many-to-one name="classes" column="classesid"/>
<filter name="filtertest" condition="id < :myid"/>
</class>
7、分页查询【重要】
* setFirstResult(),从0开始
* setMaxResults,每页显示多少条数据
List students = session.createQuery("from Student")
.setFirstResult(1)
.setMaxResults(2)
.list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Student student = (Student)iter.next();
System.out.println(student.getName());
}
8、对象导航查询,在hql中采用 . 进行导航【重要】
List students = session.createQuery("select s.name from Student s where s.classes.name like '%1%'").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
String name = (String)iter.next();
System.out.println(name);
}
9、连接查询【重要】
* 内连
* 外连接(左连接/右连接)
//List students = session.createQuery("select c.name, s.name from Student s join s.classes c").list();
List students = session.createQuery("select c.name, s.name from Student s inner join s.classes c").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
List students = session.createQuery("select c.name, s.name from Classes c left join c.students s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
List students = session.createQuery("select c.name, s.name from Classes c right join c.students s").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + "," + obj[1]);
}
10、统计查询【重要】
// List students =session.createQuery("select count(*) from Student").list();
// Long count = (Long)students.get(0);
// System.out.println(count);
Long count = (Long)session.createQuery("select count(*) from Student").uniqueResult();
System.out.println(count);
List students =session.createQuery("select c.name, count(s) from Student s join s.classes c " +
"group by c.name order by c.name").list();
for (Iterator iter=students.iterator(); iter.hasNext();) {
Object[] obj = (Object[])iter.next();
System.out.println(obj[0] + ", " + obj[1]);
}
11、DML风格的操作(尽量少用,因为和缓存不同步)
session.createQuery("update Student s set s.name=? where s.id < ?")
.setParameter(0, "李四")
.setParameter(1, 5)
.executeUpdate();