Hibernate_组件映射

Hibernate中如果表中信息太多，可以讲表中信息分成多个部分也射到类中，这就是组件。

比如学生有身体状况和学习成绩两部分信息，下面例子是组件的使用方法：

Info.java:

/**
 * 学生身体状况信息
 * 
 * @author Caihanyuan
 * @time 2012-8-24 上午10:43:07
 */
public class Info {
    private double height;
    private double weight;

    public Info() {

    }

    public Info(double height, double weight) {
        this.height = height;
        this.weight = weight;
    }
 
        //getter和setter方法
}

Report.java:

/**
 * 学生成绩信息
 * 
 * @author Caihanyuan
 * @time 2012-8-24 上午10:44:01
 */
public class Report {
    private int math;
    private int chinese;
    private int english;

    public Report() {

    }

    public Report(int math, int chinese, int english) {
        super();
        this.math = math;
        this.chinese = chinese;
        this.english = english;
    }

       //省略getter,setter
}

Student.java:

/**
 * 学生实体类，对应于表格student
 * 
 * @author Caihanyuan
 * @time 2012-8-24 上午10:42:53
 */
public class Student {
    private String id;
    private String name;
    private Info info;
    private Report report;

    public Student() {

    }

    public Student(String id, String name, Info info, Report report) {
        this.id = id;
        this.name = name;
        this.info = info;
        this.report = report;
    }

    //getter,setter
}

对应的配置文件：

Student.hbm.xml：

<hibernate-mapping>
    <class name="com.sunflower.pojo.Student" table="student">
        <id name="id" column="id" type="string">
            <generator class="uuid"></generator>
        </id>

        <property name="name" column="name" type="string"></property>

        <!-- 身体状况组件信息Info -->
        <component name="info" class="com.sunflower.pojo.Info">
            <property name="height" type="double"></property>
            <property name="weight" type="double"></property>
        </component>

        <!-- 成绩组件信息Report -->
        <component name="report" class="com.sunflower.pojo.Report">
            <property name="math" type="int"></property>
            <property name="chinese" type="int"></property>
            <property name="english" type="int"></property>
        </component>
    </class>
</hibernate-mapping>

反向生成表格：

drop table if exists student
create table student (id varchar(255) not null, name varchar(255), height double
precision, weight double precision, math integer, chinese integer, english integer,
primary key (id))

测试：
Test.java:

public class Test {
    public void save() {
        Session session = HibernateUtil.getSession();
        Transaction ts = session.beginTransaction();

        try {
            Info info = new Info();
            info.setHeight(1.75);
            info.setWeight(65);

            Report report = new Report();
            report.setMath(85);
            report.setChinese(90);
            report.setEnglish(95);

            Student studnet = new Student();
            studnet.setName("柳长风");
            studnet.setInfo(info);
            studnet.setReport(report);

            session.save(studnet);
            ts.commit();
        }
        catch (Exception e) {
            e.printStackTrace();
            ts.rollback();
        }
        finally {
            HibernateUtil.closeSession(session);
        }
    }

    @SuppressWarnings("unchecked")
    public void get() {

        Session session = HibernateUtil.getSession();
        Transaction ts = session.beginTransaction();

        try {
            List list = session.createQuery("from Student").list();
            Student student = (Student) list.get(0);

            System.out.println("name is:" + student.getName() + " height is:"
                    + student.getInfo().getHeight() + " weight is:"
                    + student.getInfo().getWeight());
            ts.commit();
        }
        catch (Exception e) {
            e.printStackTrace();
            ts.rollback();
        }
        finally {
            HibernateUtil.closeSession(session);
        }
    }

    public static void main(String[] args) {
        Test test = new Test();
        test.save();
        test.get();
    }
}

测试结果：

插入：

insert into student (name, height, weight, math, chinese, english, id) values
(?, ?, ?, ?, ?, ?, ?)

查询：

select student0_.id as id0_, student0_.name as name0_, student0_.height as
height0_, student0_.weight as weight0_, student0_.math as math0_, student0_.chinese as
chinese0_, student0_.english as english0_ from student student0_
name is:柳长风 　height is:1.75 　weight is:65.0

 

如果对组件进行双向映射，需要修改组件类和映射文件:

修改Info.java:

public class Info {
    private double height;
    private double weight;
    private Student student;    

    public Info() {

    }

    public Info(double height, double weight) {
        this.height = height;
        this.weight = weight;
    }
 
        //getter和setter方法
}

Student.hbm.xml:

   <!-- 身体状况组件信息Info -->
        <component name="info" class="com.sunflower.pojo.Info">
            <parent name="student"/>
            <property name="height" type="double"></property>
            <property name="weight" type="double"></property>
        </component>

在第３行中的中加入<parent/>标签就可以对组件进行反向求得整体.