Hibernate（七）

三套查询之HQL查询（原文再续书接上一回）

where子句部分(查询过滤部分)

Hibernate的where子句部分能支持的运算符，表达式、函数特别多，用法与sql语句是一样的.
常用的表达式、运算符、函数:
=、<、<=、>、>=、!=、and、or、distinct、between...and 、like、concat()、
is null, is not null, is empty, is not empty、second(...),
minute(...), hour(...), day(...), month(...)。
支持EJB-QL 3.0的函数:
trim(), lower(), upper(), length(), abs(), sqrt(), bit_length(), mod()
支持操作集合属性的函数：
size()|size, minelement(), maxelement(), minindex(), maxindex().

1.支持自定义的索引号

     //支持自定义的索引号
     @Test
     public void test5(){
         Query query = session.createQuery("select s from Student s where s.name like ?57");
         query.setParameter("57", "%ab%");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }

2.like

     　　 //like
         @Test
         public void test6(){
             Query query = session.createQuery("select s from Student s where s.name like ?3");
             query.setParameter("3", "%k%");
             List<Student> list = query.list();
             for (Student student : list) {
                 System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
             }
         }

3.between and

     //between and
     @Test
     public void test7(){
         Query query = session.createQuery("select s from Student s where s.name like ?3 and s.java between ?4 and ?5");
         query.setParameter("3", "%k%").setParameter("4", 10).setParameter("5", 80);
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getJava()+student.getTeacher().getTname());
         }
     }    

4.concat

     //concat
     @Test
     public void test8(){
         Query query = session.createQuery("select s from Student s where s.name like concat('%',?,'%')");
         query.setParameter(0, "ab");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }    

5.is not null

     //is not null
     @Test
     public void test9(){
         Query query = session.createQuery("select s from Student s where s.name is not null");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }    

6.trim

     //trim
     @Test
     public void test10(){
         Query query = session.createQuery("select s from Student s where trim(s.name) like ?");
         query.setParameter(0, "aa%");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }    

7.upper

     //upper
     @Test
     public void test11(){
         Query query = session.createQuery("select upper(s.name) from Student s where s.name like ?");
         query.setParameter(0, "%b%");
         List<String> list = query.list();
         for (String string : list) {
             System.out.println(string);
         }
     }    

8.length

     //length
     @Test
     public void test12(){
         Query query = session.createQuery("select s from Student s where length(s.name)>? ");
         query.setParameter(0, 4);
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }        

9.sqrt

     //sqrt
     @Test
     public void test13(){
         Query query = session.createQuery("select s from Student s where sqrt(s.id)=?");
         query.setParameter(0, 2.0);
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }    

10.bit_length

     //bit_length 位长度
     @Test
     public void test14(){
         Query query = session.createQuery("select bit_length(s.name) from Student s where s.id=?57");
         query.setParameter("57", 3);
         Long uniqueResult = (Long) query.uniqueResult();
         System.out.println(uniqueResult);
     }

11.mod

     //mod
     @Test
     public void test15(){//选取id为偶数的学生
         Query query = session.createQuery("select s from Student s where mod(s.id,?)=?");
         query.setParameter(0, 2);
         query.setParameter(1, 0);
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName());
         }
     }

12.size

操作集合属性的函数

     //size
     @Test
     public void test16(){
         Query query = session.createQuery("select t from Teacher t where size(t.students)>?");
         query.setParameter(0, 50);
         List<Teacher> list = query.list();
         for (Teacher teacher : list) {
             System.out.println(teacher.getTid()+teacher.getTname());
         }
         System.out.println("======================================");
         Query query1 = session.createQuery("select t from Teacher t where t.students.size>?");
         query1.setParameter(0, 30);
         List<Teacher> list1 = query1.list();
         for (Teacher teacher : list1) {
             System.out.println(teacher.getTid()+teacher.getTname());
         }
     }

13.minelement(), maxelement()

对集合中元素生成的列进行操作

     //minelement(), maxelement()  返回集合中的元素主键最大/最小的元素
     @Test
     public void test17(){
         Query query = session.createQuery("select maxelement(t.students) from Teacher t");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+":"+student.getName()+":"+student.getJava());
         }
         System.out.println("===============================");
         Query query1 = session.createQuery("select minelement(t.students) from Teacher t");
         List<Student> list1 = query1.list();
         for (Student student : list1) {
             System.out.println(student.getId()+":"+student.getName()+":"+student.getJava());
         }
     }

14.minindex(), maxindex()

对集合中的排序列进行操作。

对于索引了（有序）的集合，可以使用minindex 与 maxindex函数来引用到最小与最大的索引序数。

同理，可以使用minelement 与 maxelement函数来 引用到一个基本数据类型的集合中最小与最大的元素。（如上）

List<Order> orders = session.createQuery("select o from Order o where minindex(o.orderItems) = ?").setParameter(0,0).list();
 
List<Order> orders = session.createQuery("select o from Order o where maxindex(o.orderItems) = ?").setParameter(0,0).list();

子查询

Hibernate的子查询与SQL语句中的子查询一样，子查询部分放在in、not in里面.

     //把老师的id和学生的id一样的学生查询出来
     @Test
     public void test19(){
         Query query = session.createQuery("select s from Student s where s.id in (select t.tid from Teacher t)");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName()+student.getTeacher().getTname());
         }
     }

多态查询

当持久化类存在继承关系时，查询父类时，它会把父类所有的对象查询出来，而且也会把所有子类对象查询出来。

     //查询所有
     @Test
     public void test20(){
         //Query query = session.createQuery("select o from java.lang.Object o");
         Query query = session.createQuery("from java.lang.Object");
         List list = query.list();
         System.out.println(list.size());
     }

命名查询

把所有hql语句写在一个单独的配置文件中.
一般在实际的项目中用得比较多，它会把比较复杂的hql语句写在一个单独的配置文件中，
方便以后对hql语句进行优化，也方便统一管理.

1.第一种方式*.hbm.xml

A.创建Query.hbm.xml

在官方下载的项目里搜索*.hbm.xml，拷贝一个文件到自己的项目里，修改文件名（任意），修改文件内容：

<!-- 定义HQL查询语句 -->

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping SYSTEM "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd" >
<hibernate-mapping>
    <query name="hql_student_xml">from Student</query>
</hibernate-mapping>

B.配置到 hibernate.cfg.xml

C.代码使用

     @Test
     public void test21(){
         Query query = session.getNamedQuery("hql_student_xml");
         List<Student> list = query.list();
         for (Student student : list) {
             System.out.println(student.getId()+student.getName());
         }
     }

2.第二种方式在持久类上加注解

 package com.rong.entity.group;
 
 import javax.persistence.Entity;
 import javax.persistence.FetchType;
 import javax.persistence.GeneratedValue;
 import javax.persistence.GenerationType;
 import javax.persistence.Id;
 import javax.persistence.JoinColumn;
 import javax.persistence.ManyToOne;
 import javax.persistence.NamedQueries;
 import javax.persistence.NamedQuery;
 
 @Entity
 //配置多个命名查询hql语句
 @NamedQueries(value={@NamedQuery(name="query1",query="select s from Student s where s.name like ?")
                     ,@NamedQuery(name = "query2", query = "from Student")})
 //只能配置单个命名查询hql语句,一个类中该注解只能使用一次！
 @NamedQuery(name = "query3", query = "select count(s) from Student s")
 public class Student {
     @Id
     @GeneratedValue(strategy=GenerationType.AUTO)
     private int id;
     private String name;
     private int math;
     private int java;
     @ManyToOne(targetEntity=Teacher.class,fetch=FetchType.LAZY)
     @JoinColumn(name="t_id",referencedColumnName="tid")
     private Teacher teacher;
     public int getId() {
         return id;
     }
     public void setId(int id) {
         this.id = id;
     }
     public String getName() {
         return name;
     }
     public void setName(String name) {
         this.name = name;
     }
     public int getMath() {
         return math;
     }
     public void setMath(int math) {
         this.math = math;
     }
     public int getJava() {
         return java;
     }
     public void setJava(int java) {
         this.java = java;
     }
     public Teacher getTeacher() {
         return teacher;
     }
     public void setTeacher(Teacher teacher) {
         this.teacher = teacher;
     }
 }

     @Test
     public void test22(){
         Query query1 = session.getNamedQuery("query1");
         query1.setParameter(0, "%ab%");
         List<Student> list1 = query1.list();
         for (Student student : list1) {
             System.out.println(student.getId()+student.getName());
         }
 
         Query query2 = session.getNamedQuery("query2");
         List<Student> list2 = query2.list();
         for (Student student : list2) {
             System.out.println(student.getId()+student.getName());
         }
 
         Query query3 = session.getNamedQuery("query3");
         Object uniqueResult = query3.uniqueResult();
         System.out.println(uniqueResult);
     }