Home >Java >javaTutorial >hibernate_association mapping_one-to-many

hibernate_association mapping_one-to-many

巴扎黑
巴扎黑Original
2017-06-23 16:28:301646browse

hibernate mapping relationship

One-to-many, many-to-one,One-to-one, Many-to-many.

The commonly used ones are one-to-many and many-to-one.

In the database, you can express a one-to-many relationship by adding primary and foreign key associations; In hibernate, one party can hold multiple parties Set implementation, that is, using the element in the "one" end to represent the object holding the "many" end.

The following implements a "one-to-many" demo of addition, deletion, modification and search: one class corresponds to multiple students.

First create the student class Student

##
 1 package com.imooc.entity; 2  3 import java.io.Serializable; 4  5 public class Student implements Serializable { 6  7     private int sid; 8     private String sname; 9     private String sex;10     // 在多方定义一个一方的引用11     private Grade grade;12     13     public int getSid() {14         return sid;15     }16     public void setSid(int sid) {17         this.sid = sid;18     }19     public String getSname() {20         return sname;21     }22     public void setSname(String sname) {23         this.sname = sname;24     }25     public String getSex() {26         return sex;27     }28     public void setSex(String sex) {29         this.sex = sex;30     }31     public Grade getGrade() {32         return grade;33     }34     public void setGrade(Grade grade) {35         this.grade = grade;36     }37     38     public Student() {39         super();40     }41     42     public Student(String sname, String sex) {43         super();44         this.sname = sname;45         this.sex = sex;46     }47     48 }
View Code

Create class Grade

 1 package com.imooc.entity; 2  3 import java.io.Serializable; 4 import java.util.HashSet; 5 import java.util.Set; 6  7  8 public class Grade implements Serializable { 9 10     private int gid;11     private String gname;12     private String gdesc;13     private Set<Student> students = new HashSet<Student>();14     15     public int getGid() {16         return gid;17     }18     public void setGid(int gid) {19         this.gid = gid;20     }21     public String getGname() {22         return gname;23     }24     public void setGname(String gname) {25         this.gname = gname;26     }27     public String getGdesc() {28         return gdesc;29     }30     public void setGdesc(String gdesc) {31         this.gdesc = gdesc;32     }33     public Set<Student> getStudents() {34         return students;35     }36     public void setStudents(Set<Student> students) {37         this.students = students;38     }39     40     public Grade() {41         super();42     }43     44     public Grade(int gid, String gname, String gdesc) {45         super();46         this.gid = gid;47         this.gname = gname;48         this.gdesc = gdesc;49     }50     51     public Grade(String gname, String gdesc) {52         super();53         this.gname = gname;54         this.gdesc = gdesc;55     }56 }
View Code

Create the mapping file Student.hbm.xml of the Student class

 1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2017-6-1 14:49:09 by Hibernate Tools 3.5.0.Final --> 5 <hibernate-mapping> 6     <class name="com.imooc.entity.Student" table="STUDENT"> 7         <id name="sid" type="int"> 8             <column name="SID" /> 9             <generator class="increment" />10         </id>11         <property name="sname" type="java.lang.String">12             <column name="SNAME" />13         </property>14         <property name="sex" type="java.lang.String">15             <column name="SEX" />16         </property>17     </class>18 </hibernate-mapping>
View Code

Create the mapping file Grade.hbm.xml of the Grade class

 1 <?xml version="1.0"?> 2 <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 3 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 4 <!-- Generated 2017-6-1 14:49:09 by Hibernate Tools 3.5.0.Final --> 5 <hibernate-mapping> 6     <class name="com.imooc.entity.Grade" table="GRADE"> 7         <id name="gid" type="int"> 8             <column name="GID" /> 9             <generator class="increment" />10         </id>11         <property name="gname" type="java.lang.String">12             <column name="GNAME" length="20" not-null="true" />13         </property>14         <property name="gdesc" type="java.lang.String">15             <column name="GDESC" />16         </property>17         <!-- 指定关联的外键列 -->18         <set name="students" table="STUDENT">19             <key>20                 <column name="GID" />21             </key>22             <one-to-many class="com.imooc.entity.Student" />23         </set>24     </class>25 </hibernate-mapping>
View Code

Create hibernate configuration file

 1 <?xml version="1.0" encoding="UTF-8"?> 2 <!DOCTYPE hibernate-configuration PUBLIC 3         "-//Hibernate/Hibernate Configuration DTD 3.0//EN" 4         "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd"> 5 <hibernate-configuration> 6     <session-factory> 7         <property name="connection.username">root</property> 8         <property name="connection.password">root</property> 9         <property name="connection.driver_class">com.mysql.jdbc.Driver</property>10         <property name="connection.url">11             <![CDATA[12                 jdbc:mysql://localhost:3306/hibernate?useUnicode=true&amp;characterEncoding=UTF-813             ]]>14         </property>15         <property name="dialect">org.hibernate.dialect.MySQLDialect</property>16         <property name="show_sql">true</property>17         <property name="format_sql">true</property>18         <property name="hbm2ddl.auto">update</property>19         20         <!-- 指定映射文件的路径 -->21         <mapping resource="com/imooc/entity/Grade.hbm.xml" />22         <mapping resource="com/imooc/entity/Student.hbm.xml" />23     </session-factory>24 </hibernate-configuration>
View Code

Write a test file for addition, deletion, modification and query

##
 1 package com.imooc.test; 2  3 import java.util.Set; 4  5 import org.hibernate.Session; 6 import org.hibernate.Transaction; 7  8 import com.imooc.entity.Grade; 9 import com.imooc.entity.Student;10 import com.imooc.util.HibernateUtil;11 12 /*13  * 单向一对多关系关系(班级--->学生)14  * 建立关联关系后,可以方便的从一个对象导航到另一个对象15  * 注意关联的方向16  */17 public class Test01 {18 19     public static void main(String[] args) {20         //add();21         //findStudentsByGrade();22         //update();23         delete();24     }25     26     //将学生添加到班级27     public static void add() {28         Grade g = new Grade("Java一班", "Java软件开发一班");29         Student s1 = new Student("杨康", "男");30         Student s2 = new Student("穆念慈", "女");31         32         //如果希望在学生表中添加对应的班级编号,需要在班级中添加学生,建立关联关系33         g.getStudents().add(s1);34         g.getStudents().add(s2);35         36         Session session = HibernateUtil.getSession();37         Transaction tr = session.beginTransaction();38         session.save(g);39         session.save(s1);40         session.save(s2);41         tr.commit();42         HibernateUtil.closeSession(session);43     }44     45     //查询班级中包含的学生46     public static void findStudentsByGrade() {47         Session session = HibernateUtil.getSession();48         Grade grade = (Grade) session.get(Grade.class, 1);49         System.out.println( grade.getGname() + "," + grade.getGdesc() );50         51         Set<Student> students = grade.getStudents();52         for(Student s : students) {53             System.out.println( s.getSname() + "," + s.getSex() );54         }55     }56     57     //修改学生信息58     public static void update() {59         Grade g=new Grade("Java二班", "Java软件开发二班");60         Session session = HibernateUtil.getSession();61         Transaction tr = session.beginTransaction();62         Student s = (Student) session.get(Student.class, 1);63         g.getStudents().add(s);64         session.save(g);65         tr.commit();66         HibernateUtil.closeSession(session);67     }68     69     //删除学生信息70     public static void delete() {71         Session session = HibernateUtil.getSession();72         Transaction tr = session.beginTransaction();73         Student s = (Student) session.get(Student.class, 2);74         session.delete(s);75         tr.commit();76         HibernateUtil.closeSession(session);77     }78 }
View Code

The above is the detailed content of hibernate_association mapping_one-to-many. For more information, please follow other related articles on the PHP Chinese website!

Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn