hibernate的多表关联

话不多说，直接上代码示例

1、父表的POJO类InternationalClass.java

package com.international.model;

import java.util.Set;

public class InternationalClass {
    private int classId;
    private String className;
    private String grade;
    private String major;
    private String reserves1;
    private String reserves2;
    private String reserves3;
    
    private Set<InternationalStudent> interStudents;  //关联的对象
    
    public Set<InternationalStudent> getInterStudents() {
        return interStudents;
    }
    public void setInterStudents(Set<InternationalStudent> interStudents) {
        this.interStudents = interStudents;
    }
    public int getClassId() {
        return classId;
    }
    public void setClassId(int classId) {
        this.classId = classId;
    }
    public String getClassName() {
        return className;
    }
    public void setClassName(String className) {
        this.className = className;
    }
    public String getGrade() {
        return grade;
    }
    public void setGrade(String grade) {
        this.grade = grade;
    }
    public String getMajor() {
        return major;
    }
    public void setMajor(String major) {
        this.major = major;
    }
    public String getReserves1() {
        return reserves1;
    }
    public void setReserves1(String reserves1) {
        this.reserves1 = reserves1;
    }
    public String getReserves2() {
        return reserves2;
    }
    public void setReserves2(String reserves2) {
        this.reserves2 = reserves2;
    }
    public String getReserves3() {
        return reserves3;
    }
    public void setReserves3(String reserves3) {
        this.reserves3 = reserves3;
    }
}

2、父表的映射文件InternationalClass.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.international.model.InternationalClass" table="InternationalClass">
        <id name="classId" column="classId">
            <!-- 自增主键策略 -->
            <generator class="native"></generator>
        </id>
        <property name="className" column="className"></property>
        <property name="grade" column="grade"></property>
        <property name="major" column="major"></property>

        <property name="reserves1" column="reserves1"></property>
        <property name="reserves2" column="reserves2"></property>
        <property name="reserves3" column="reserves3"></property>

        <!-- 关联的国际班学生对象 -->
        <set name="interStudents" cascade="all" table="internationalStudent" inverse="true">
            <key column="classId" not-null="true"></key>
            <one-to-many class="com.international.model.InternationalStudent"/>
        </set>
    </class>
</hibernate-mapping>

3、子表的POJO类InternationalStudent.java

package com.international.model;

public class InternationalStudent {
    private String studentId;
    private String studentName;
    private String sex;
    private String password; 
    private String status;
    private String reserves1;
    private String reserves2;
    private String reserves3;
    
    private InternationalClass classes;     //定义InternationalClass类的classes对象

    public String getStudentId() {
        return studentId;
    }
    public void setStudentId(String studentId) {
        this.studentId = studentId;
    }
    public String getStudentName() {
        return studentName;
    }
    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }
    public String getStatus() {
        return status;
    }
    public void setStatus(String status) {
        this.status = status;
    }
    public String getReserves1() {
        return reserves1;
    }
    public void setReserves1(String reserves1) {
        this.reserves1 = reserves1;
    }
    public String getReserves2() {
        return reserves2;
    }
    public void setReserves2(String reserves2) {
        this.reserves2 = reserves2;
    }
    public String getReserves3() {
        return reserves3;
    }
    public void setReserves3(String reserves3) {
        this.reserves3 = reserves3;
    }
    public InternationalClass getClasses() {
        return classes;
    }
    public void setClasses(InternationalClass classes) {
        this.classes = classes;
    }
}

4、子表的映射文件InterantionalStudent.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.international.model.InternationalStudent" table="InternationalStudent">
        <id name="studentId" column="studentId">
            <!-- 非自增主键生成策略 -->
            <generator class="assigned"></generator>
        </id>
        <property name="studentName" column="studentName"></property>
        <property name="sex" column="sex"></property>
        <property name="password" column="password"></property>
        <property name="status" column="status"></property>
        <!-- <property name="classId" column="classId"></property> -->
        
        <!-- 双向n->1关联，外键，由InternationalStudent指向InternationalClass -->
        <many-to-one name="classes" class="com.international.model.InternationalClass" 
        lazy="false" fetch="join" column="classId" />
    </class>
</hibernate-mapping>

分析，上面就是两张表关联起来的映射文件和POJO类了，没贴业务代码。注意里面起关联的部分，还有cascade=“all”这个属性，我曾在父子表都设置过，然后子表执行删除操作的时候，悲剧来了，级联操作把父表对应的班级信息给我删了。。。所以导致子表的学生信息也对应没了。所以要想做到删除学生信息不影响班级信息，删除班级信息会影响学生信息，此时在子表的cascade级联属性就得设置成cascade="none"或者不写默认就是none。