hibernate與mysql數據庫級聯關係

由於代碼衆多，所以哎本篇博客中只例舉了重要代碼（本篇適合有一定hibernate基礎的學者閱讀，望多多包涵）

A、一對多one-to-many級聯

1、創建一個java工程，在工程中創建一個lib文件夾，存放 jarbao並且build path。（標註的是測試所需包，如果編輯器自帶，可以不考）

2、創建配置文件hibernate.cfg.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <!-- 一個sessionFactory代表數據庫的一個連接 -->
<session-factory>
    <!-- 鏈接數據庫的用戶名 -->
    <property name="connection.username">root</property>
    <!-- 鏈接數據庫的密碼 -->
    <property name="connection.password">newstar</property>
    <!-- 鏈接數據庫的驅動 -->
    <property name="connection.driver_class">
        com.mysql.jdbc.Driver
    </property>

    <!-- 鏈接數據庫的url -->
    <property name="connection.url">
        <![CDATA[jdbc:mysql://localhost:3306/hibernate?useUnicode=true&characterEncoding=utf8]]>
    </property>
    <!-- 方言 告訴hibernate使用哪個數據庫，hibernate就會在底層拼接相應的sql語句 -->
    <property name="dialect">
        org.hibernate.dialect.MySQLDialect
    </property>
    <!-- 根據持久化類生成表的策略 validate 通過映射文件檢查持久化淚idea匹配 update hibernate每次啓動的時候，檢查表是否存在，弱國不存在，則創建，如果存在，則說明不進行任何操作 
        create hibernate每次啓動的時候，根據持久化類和映射文件生成表 create-drop hibernate每次啓動的時候，根據持久化類和映射文件生成表，之後再刪除 -->
    <property name="hbm2ddl.auto">update</property>
    <!-- 顯示sql語句(開發中寫上，方便開發觀察) -->
    <property name="show_sql">true</property>
    <!-- 映射文件， -->
    <property name="format_sql">true</property>
    <property name="current_session_context_class">thread</property>
    <mapping resource="com/itstar/domain/Classes.hbm.xml" />
    <mapping resource="com/itstar/domain/Student.hbm.xml" />

</session-factory>



</hibernate-configuration>

3、創建持久化類Classes和Student

package com.itstar.domain;

import java.io.Serializable;
import java.util.Set;

public class Classes implements Serializable {
    private Long cid;
    private String name;
    private Set<Student> students;
    public Long getCid() {
        return cid;
    }
    public void setCid(Long cid) {
        this.cid = cid;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
}

package com.itstar.domain;

import java.io.Serializable;

public class Student implements Serializable {
    private Long sid;
    private String name;
    private String sex;
    public Long getSid() {
        return sid;
    }
    public void setSid(Long sid) {
        this.sid = sid;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }

}

4、創建兩個持久化類的映射配置文件Classes.hbm.xml和Student.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <!-- hibernate映射文件 -->
    <class name="com.itstar.domain.Classes" table="classes">
        <id name="cid" column="cid" length="5">
            <generator class="increment"></generator>
        </id>
        <property name="name" length="20"></property>
        <set name="students" cascade="save-update" inverse="false">
            <key><column name="cid"></column></key>
            <one-to-many class="com.itstar.domain.Student"/>
        </set>
    </class>

</hibernate-mapping>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <!-- hibernate映射文件 -->
    <class name="com.itstar.domain.Student" table="student">
    <id name="sid" length="5">
    <generator class="increment"></generator></id>
    <property name="name" length="20"></property>
    <property name="sex" length="4"></property>
    </class>

</hibernate-mapping>

5、進行測試

import java.util.HashSet;
import java.util.Set;

import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;
import org.hibernate.classic.Session;
import org.junit.Test;

import com.itstar.domain.Classes;
import com.itstar.domain.Student;
import com.itstar.util.SessionUtil;



public class TestOneTOMany {
    private SessionUtil sessionUtil = new SessionUtil();

    /**
     * 創建數據
     */
    @Test
    public void testCreateTables(){
        Configuration configuration = new Configuration();
        configuration.configure();
        SessionFactory sessionFctory = configuration.buildSessionFactory();
        Session session = sessionFctory.getCurrentSession();
        Transaction transaction = session.beginTransaction();
        Classes classes = new Classes();
        classes.setName("計算機1班");

        Student student = new Student();
        student.setName("張三");
        student.setSex("男");

        session.save(classes);
        session.save(student);
        transaction.commit();
    }
    }

B.多對一many-to-one

在Student.hbm.xml加入以下代碼即可

<!-- 
            外鍵
              column
         -->
        <many-to-one name="classes" column="cid" class="com.itheima12.hibernate.domain.Classes" cascade="save-update"></many-to-one>
    </class>

C.many-to-many

java類有點改動，兩個類都含有set屬性（大同小異），配置文件

<set name="courses" table="student_course" cascade="save-update">
            <key>
                <!-- 
                    外鍵
                 -->
                <column name="sid"></column>
            </key>
            <!-- 
                column外鍵
             -->
            <many-to-many class="com.itheima12.hibernate.domain.Course" column="cid"></many-to-many>
        </set>

和

<set name="students" table="student_course">
            <key>
                <!-- 
                    外鍵
                 -->
                <column name="cid"></column>
            </key>
            <!-- 
                column外鍵
             -->
            <many-to-many class="com.itheima12.hibernate.domain.Student" column="sid"></many-to-many>
        </set>

即可

一對一one-to-one更簡單，加入unique=“true

”

<many-to-one name="classes" column="cid" class="com.itheima12.hibernate.domain.Classes" 
             unique="true"