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hql查询语句内存中的情况，fetch迫切查询关键字

Classes.java

 1 package cn.itcast.hiberate.sh.domain;
 2 
 3 import java.io.Serializable;
 4 import java.util.Set;
 5 
 6 public class Classes implements Serializable{
 7     private Long cid;
 8     private String cname;
 9     private String description;
10     
11     public Classes(){}
12     
13     public Classes(String cname,String description){
14         this.cname = cname;
15         this.description = description;
16     }
17     
18     public Long getCid() {
19         return cid;
20     }
21 
22     public void setCid(Long cid) {
23         this.cid = cid;
24     }
25 
26     public String getCname() {
27         return cname;
28     }
29 
30     public void setCname(String cname) {
31         this.cname = cname;
32     }
33 
34     public String getDescription() {
35         return description;
36     }
37 
38     public void setDescription(String description) {
39         this.description = description;
40     }
41 
42     public Set<Student> getStudents() {
43         return students;
44     }
45 
46     public void setStudents(Set<Student> students) {
47         this.students = students;
48     }
49 
50     private Set students;
51 }

View Code

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <hibernate-mapping>
 5     <class name="cn.itcast.hiberate.sh.domain.Classes">
 6         <id name="cid" length="5" type="java.lang.Long">
 7             <generator class="increment"></generator>
 8         </id>
 9         <property name="cname" length="20" type="java.lang.String"></property>
10         
11         <property name="description" length="100" type="java.lang.String"></property>
12         <!-- 
13             set元素对应类中的set集合
14             通过set元素使classes表与student表建立关联
15                key是通过外键的形式让两张表建立关联
16                one-to-many是通过类的形式让两个类建立关联
17             
18             cascade 级联
19                save-update
20                    1、当 保存班级的时候，对学生进行怎么样的操作
21                         如果学生对象在数据库中没有对应的值，这个时候会执行save操作
22                         如果学生对象在数据库中有对应的值，这个时候会执行update操作
23                delete
24                all
25             inverse  维护关系
26                true      不维护关系     
27                false     维护关系
28                default   false
29          -->
30         <set name="students" cascade="save-update" inverse="true" lazy="false" fetch="join">
31             <!-- 
32                 key是用来描述外键
33              -->
34             <key>
35                 <column name="cid"></column>
36             </key>
37             <one-to-many class="cn.itcast.hiberate.sh.domain.Student"/>
38         </set>
39     </class>
40 </hibernate-mapping>

View Code

Course.java

 1 package cn.itcast.hiberate.sh.domain;
 2 
 3 import java.io.Serializable;
 4 import java.util.Set;
 5 
 6 public class Course implements Serializable{
 7     private Long cid;
 8     private String cname;
 9     private String description;
10     
11     public Long getCid() {
12         return cid;
13     }
14 
15     public void setCid(Long cid) {
16         this.cid = cid;
17     }
18 
19     public String getCname() {
20         return cname;
21     }
22 
23     public void setCname(String cname) {
24         this.cname = cname;
25     }
26 
27     public String getDescription() {
28         return description;
29     }
30 
31     public void setDescription(String description) {
32         this.description = description;
33     }
34 
35     public Set<Student> getStudents() {
36         return students;
37     }
38 
39     public void setStudents(Set<Student> students) {
40         this.students = students;
41     }
42 
43     private Set<Student> students;
44 }

View Code

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <!-- 
 5     建立表和类的对应关系
 6  -->
 7 <hibernate-mapping>
 8     <class name="cn.itcast.hiberate.sh.domain.Course">
 9         <id name="cid" type="java.lang.Long" length="5">
10             <generator class="increment"></generator>
11         </id>
12         <property name="cname" type="java.lang.String" length="20"></property>
13         <property name="description" type="java.lang.String" length="50"></property>
14         <!-- 
15             table
16                student与course在数据库的层次上通过该表实现关联
17          -->
18         <set name="students" table="student_course">
19             <key>
20             <!-- 
21                 在哪个映射文件中，就添加哪个
22              -->
23                 <column name="cid"></column>
24             </key>
25             <!-- 
26                 column表示外键
27              -->
28             <many-to-many class="cn.itcast.hiberate.sh.domain.Student" column="sid"></many-to-many>
29         </set>
30     </class>
31 </hibernate-mapping>

View Code

Student.java

 1 package cn.itcast.hiberate.sh.domain;
 2 
 3 import java.io.Serializable;
 4 import java.util.HashSet;
 5 import java.util.Set;
 6 
 7 public class Student implements Serializable{
 8     private Long sid;
 9     private String sname;
10     
11     private Classes classes;
12     
13     private Set<Course> courses = new HashSet<Course>(0);
14     
15     public Set<Course> getCourses() {
16         return courses;
17     }
18     public void setCourses(Set<Course> courses) {
19         this.courses = courses;
20     }
21     public Classes getClasses() {
22         return classes;
23     }
24     public void setClasses(Classes classes) {
25         this.classes = classes;
26     }
27     public Long getSid() {
28         return sid;
29     }
30     public void setSid(Long sid) {
31         this.sid = sid;
32     }
33     public String getSname() {
34         return sname;
35     }
36     public void setSname(String sname) {
37         this.sname = sname;
38     }
39     public String getDescription() {
40         return description;
41     }
42     public void setDescription(String description) {
43         this.description = description;
44     }
45     private String description;
46 }

View Code

 1 <?xml version="1.0" encoding="utf-8"?>
 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
 4 <hibernate-mapping>
 5     <class name="cn.itcast.hiberate.sh.domain.Classes">
 6         <id name="cid" length="5" type="java.lang.Long">
 7             <generator class="increment"></generator>
 8         </id>
 9         <property name="cname" length="20" type="java.lang.String"></property>
10         
11         <property name="description" length="100" type="java.lang.String"></property>
12         <!-- 
13             set元素对应类中的set集合
14             通过set元素使classes表与student表建立关联
15                key是通过外键的形式让两张表建立关联
16                one-to-many是通过类的形式让两个类建立关联
17             
18             cascade 级联
19                save-update
20                    1、当 保存班级的时候，对学生进行怎么样的操作
21                         如果学生对象在数据库中没有对应的值，这个时候会执行save操作
22                         如果学生对象在数据库中有对应的值，这个时候会执行update操作
23                delete
24                all
25             inverse  维护关系
26                true      不维护关系     
27                false     维护关系
28                default   false
29          -->
30         <set name="students" cascade="save-update" inverse="true" lazy="false" fetch="join">
31             <!-- 
32                 key是用来描述外键
33              -->
34             <key>
35                 <column name="cid"></column>
36             </key>
37             <one-to-many class="cn.itcast.hiberate.sh.domain.Student"/>
38         </set>
39     </class>
40 </hibernate-mapping>

View Code

Hibernate.cfg.xml

 1 <?xml version='1.0' encoding='utf-8'?>
 2 <!DOCTYPE hibernate-configuration PUBLIC
 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
 4         "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
 5 <hibernate-configuration>
 6     <!-- 
 7         一个session-factory只能连接一个数据库
 8     -->
 9 <session-factory>
10     <!-- 
11         数据库的用户名
12     -->
13     <property name="connection.username">root</property>
14 
15     <property name="connection.driver_class">
16         com.mysql.jdbc.Driver
17     </property>
18 
19     <!-- 
20         密码
21     -->
22     <property name="connection.password">friends</property>
23     <!-- 
24         url
25     -->
26     <property name="connection.url">
27         jdbc:mysql://localhost:3306/mydatabase
28     </property>
29     <!-- 
30         作用：根据持久化类和映射文件生成表
31         validate
32         create-drop
33         create
34         update
35     -->
36     <property name="hbm2ddl.auto">update</property>
37 
38     <property name="hibernate.dialect">
39         org.hibernate.dialect.MySQLInnoDBDialect
40     </property>
41     <!-- 
42         显示hibernate内部生成的sql语句
43     -->
44     <property name="show_sql">true</property>
45     <property name="format_sql">true</property>
46     <mapping resource="cn/itcast/hiberate/sh/domain/Classes.hbm.xml" />
47     <mapping resource="cn/itcast/hiberate/sh/domain/Student.hbm.xml" />
48      <mapping resource="cn/itcast/hiberate/sh/domain/Course.hbm.xml" /> 
49 
50 </session-factory>
51 </hibernate-configuration>

View Code

  1 package cn.itcast.hibernate.sh.dao;
  2 
  3 import java.util.ArrayList;
  4 import java.util.HashSet;
  5 import java.util.List;
  6 import java.util.Set;
  7 
  8 import org.hibernate.Query;
  9 import org.hibernate.Session;
 10 import org.junit.Test;
 11 
 12 import cn.itcast.hiberate.sh.domain.Classes;
 13 import cn.itcast.hiberate.sh.domain.Course;
 14 import cn.itcast.hiberate.sh.domain.Student;
 15 import cn.itcast.hibernate.sh.utils.HiberanteUtils;
 16 
 17 /**
 18  * 单表
 19  * 
 20  * 一对多和多对多
 21  * 
 22  * 多表的结合
 23  * @author Think
 24  *
 25  */
 26 public class HQLDao extends HiberanteUtils{
 27     public List<Classes> queryAllClasses(){
 28         Session session = sessionFactory.openSession();
 29         List<Classes> cList = session.createQuery("from Classes").list();
 30         session.close();
 31         return cList;
 32     }
 33     
 34     public List queryClasses_Properties(){
 35         Session session = sessionFactory.openSession();
 36         List cList = session.createQuery("select cid,cname from Classes").list();
 37         session.close();
 38         return cList;
 39     }
 40     
 41     public List<Classes> queryClasses_Constructor(){
 42         Session session = sessionFactory.openSession();
 43         List<Classes> cList = session.createQuery("select new cn.itcast.hiberate.sh.domain.Classes(cname,description) from Classes").list();
 44         session.close();
 45         return cList;
 46     }
 47     
 48     public Classes queryClasses_Condition(){
 49         Session session = sessionFactory.openSession();
 50         Query query = session.createQuery("select new cn.itcast.hiberate.sh.domain.Classes(cname,description) from Classes where cid=:cid");
 51         query.setLong("cid", 1L);
 52         Classes classes = (Classes)query.uniqueResult();
 53         System.out.println(classes.getCname());
 54         session.close();
 55         return classes;
 56     }
 57     
 58     public Classes queryClasses_Condition_2(){
 59         Session session = sessionFactory.openSession();
 60         Query query = session.createQuery("select new cn.itcast.hiberate.sh.domain.Classes(cname,description) from Classes where cid=?");
 61         query.setLong(0, 1L);
 62         Classes classes = (Classes)query.uniqueResult();
 63         System.out.println(classes.getCname());
 64         session.close();
 65         return classes;
 66     }
 67     
 68     /**
 69      * order by,group by,sun,min,max,avg,having等都适用
 70      * @return
 71      */
 72     
 73     /**
 74      * 子查询
 75      */
 76     public void queryClasses_SubSelect(){
 77         Session session = sessionFactory.openSession();
 78         List<Classes> cList = session.createQuery("from Classes where cid in(select cid from Classes where cid in(1,2,3))").list();
 79         session.close();
 80     }
 81     
 82     public static HQLDao getInstance(){
 83         return new HQLDao();
 84     }
 85     
 86     /*********************************************************************************************/
 87        /**
 88         * 一对多
 89         *    等值连接          查询出来的机构很差  
 90         *    内连接  
 91         *    左外连接  
 92         *    迫切左外连接
 93         */
 94     public List<Classes> queryClasses_Student_EQ(){
 95         Session session = sessionFactory.openSession();
 96         List<Classes> cList = session.createQuery("from Classes c,Student s where c.cid=s.classes.cid").list();
 97         session.close();
 98         return cList;
 99     }
100     
101     /**
102      * 内连接
103      * @return
104      */
105     public List<Classes> queryClasses_Student_INNER(){
106         Session session = sessionFactory.openSession();
107         List<Classes> cList = session.createQuery("from Classes c inner join c.students").list();
108         session.close();
109         return cList;
110     }
111     
112     /**
113      * 迫切内连接
114      * @return
115      */
116     public List<Classes> queryClasses_Student_INNER_FETCH(){
117         Session session = sessionFactory.openSession();
118         List<Classes> cList = session.createQuery("from Classes c inner join fetch c.students").list();
119         session.close();
120         return cList;
121     }
122     
123     /**
124      * 左外连接
125      */
126     public List<Classes> queryClasses_Student_LeftJoin(){
127         Session session = sessionFactory.openSession();
128         List<Classes> cList = session.createQuery("from Classes c left outer join c.students").list();
129         session.close();
130         return cList;
131     }
132     
133     /**
134      * 迫切左外连接
135      */
136     public List<Classes> queryClasses_Student_LeftJoin_fetch(){
137         Session session = sessionFactory.openSession();
138         String hql = "from Classes c left outer join fetch c.students";
139         hql = "from Student s left outer join fetch s.classes c";
140         List<Classes> cList = session.createQuery(hql).list();
141         session.close();
142         return cList;
143     }
144     
145     /**
146      * 带select的查询
147      */
148     public List<Classes> queryClasses_Student_Select(){
149         Session session = sessionFactory.openSession();
150         String hql = "select new cn.itcast.hiberate.sh.domain.ClassesView(c.cname,s.sname) " +
151                      "from Student s left outer join s.classes c";
152         List<Classes> cList = session.createQuery(hql).list();
153         session.close();
154         return cList;
155     }
156     
157     /**
158      * 多对多
159      */
160     public void testQueryCourse_Student(){
161         Session session = sessionFactory.openSession();
162         List<Student> studentList = session.createQuery("from Student s inner join fetch s.courses c").list();
163         session.close();
164     }
165     
166     
167     /**
168      * 一对多结合多对多
169      */
170     public List<Student> queryClasses_Student_Course(){
171         Session session = sessionFactory.openSession();
172         String hql = "from Classes cs inner join fetch cs.students s inner join fetch s.courses c";
173         hql = "from Student s inner join fetch s.classes cs inner join fetch s.courses c";
174         //hql = "from Classes cs left outer join fetch cs.students s left outer join fetch s.courses c";
175         List<Student> cList = session.createQuery(hql).list();
176 //        Set<Classes> cset = new HashSet<Classes>(cList);
177 //        cList = new ArrayList<Classes>(cset);
178         System.out.println(cList.size());
179 //        for(Classes classes:cList){
180 //            System.out.println(classes.getCid());
181 //            Set<Student> students = classes.getStudents();
182 //            for(Student student:students){
183 //                System.out.println(student.getSname());
184 //                Set<Course> courses = student.getCourses();
185 //                for(Course course:courses){
186 //                    System.out.println(course.getCname());
187 //                }
188 //            }
189 //        }
190         session.close();
191         return cList;
192     }
193 }

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原文地址：https://www.cnblogs.com/friends-wf/p/3779747.html

hql查询语句 内存中的情况，fetch迫切查询关键字

hql查询语句内存中的情况，fetch迫切查询关键字