Hibernate 组合主键映射、大对象映射、组件映射

通过组件来实现组合主键的步骤：
这里举个例子，一个表有学生编号，科目编号，成绩，显然学生编号和科目编号的组合才能作为主键

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1.编写组合主键的属性的类，该类必须实现Serializable

public class ScoreId implements Serializable {    private  int stuId;//学生编号    private  int subjectId;//科目编号    public int getSubjectId() {        return subjectId;    }    public void setSubjectId(int subjectId) {        this.subjectId = subjectId;    }    public int getStuId() {        return stuId;    }    public void setStuId(int stuId) {        this.stuId = stuId;    }}

2 .主类

public class Score {    private ScoreId scoreId;    private double result;//成绩    public ScoreId getScoreId() {        return scoreId;    }    public void setScoreId(ScoreId scoreId) {        this.scoreId = scoreId;    }    public double getResult() {        return result;    }    public void setResult(double result) {        this.result = result;    }}

3 .映射文件编写

<hibernate-mapping package="cn.siggy.pojo">    <class name="Score">        <composite-id name="scoreId" class="ScoreId">            <key-property name="stuId"></key-property>            <key-property name="subjectId"></key-property>        </composite-id>        <property name="result"></property>    </class></hibernate-mapping>

4 .测试（session对象获得等封装在了HibernateUtil里面，略）

@Test    public void testSave() throws HibernateException{        Session session=null;        Transaction tx=null;        try{            session=HibernateUtil.getSession();            tx=session.beginTransaction();            Score s=new Score();            ScoreId sid=new ScoreId();            sid.setStuId(2);            sid.setSubjectId(6);            s.setResult(89);            s.setScoreId(sid);            session.save(s);            tx.commit();        }        catch(HibernateException e){            if(tx!=null){                tx.rollback();                e.printStackTrace();                throw  e;            }        }finally{            HibernateUtil.closeSession();        }    }

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大对象映射
在pojo类中使用了大对象，比如Blob类和Clob类。比如Blob我们以前都是通过文件上传来来存储图片，如果我们要把它存放到数据库，那么如下。
1.pojo类

public class Student {    private int id;    private String name;    private int age;    //存放大数据  可以存放4G的内容    private Blob image;    private Clob introduce;//省略get/set    }

2.hbm配置 需要指定大对象的类型

<hibernate-mapping package="cn.siggy.pojo">    <class name="Student">        <id name="id">            <generator class="native"></generator>        </id>        <property name="name"/>        <property name="age"/>        <property name="image" type="java.sql.Blob"/>        <property name="introduce" type="java.sql.Clob"/>    </class></hibernate-mapping>

3.测试（session对象获得等封装在了HibernateUtil里面，略）

@Test    public void testSave() throws HibernateException, SerialException, SQLException{        Session session=null;        Transaction tx=null;        try{            session=HibernateUtil.getSession();            tx=session.beginTransaction();            Student stu = new Student();            stu.setName("尹志平");            stu.setAge(23);            Blob blob = new SerialBlob("ttt".getBytes());            Clob clob = new SerialClob("sss".toCharArray());            stu.setImage(blob);            stu.setIntroduce(clob);            session.save(stu);            tx.commit();        }        catch(HibernateException e){            if(tx!=null){                tx.rollback();                e.printStackTrace();                throw  e;            }        }finally{            HibernateUtil.closeSession();        }    }

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组件是一个被包含的对象 比如这里指一个人有很多个地址，直接把地址值写在一张表的时候，只涉及一张表，没有建立另外一张表和这种表地址id的外键，这个时候用主键。（但是不推荐这种表关系，因为这样维护起来很麻烦）

主类

public class Teacher {    private int id;    private String name;    private String sex;    private Address address;//省略get/set    }

类Teacher的组件

public class Address {    private String addr1;    private String addr2;    private String addr3;    //省略get/set}

Teacher.hbm.xml

<hibernate-mapping package="cn.siggy.pojo">    <class name="Teacher">        <id name="id">            <generator class="native"></generator>        </id>        <property name="name"/>        <property name="sex"/>        <!-- 组件 -->        <component name="address" class="Address">            <property name="addr1"/>            <property name="addr2"/>            <property name="addr3"/>        </component>    </class></hibernate-mapping>

测试（session对象获得等封装在了HibernateUtil里面，略）

@Test    public void testSave() throws HibernateException, SerialException, SQLException{        Session session = null;        Transaction tx = null;        try{            session = HibernateUtil.getSession();            tx = session.beginTransaction();            Teacher t = new Teacher();            t.setName("老裴");            t.setSex("男");            Address address = new Address();            address.setAddr1("西三旗");            address.setAddr2("西直门");            address.setAddr3("南六环");            t.setAddress(address);            session.save(t);            tx.commit();        }catch (HibernateException e) {            if(tx!=null)                tx.rollback();            e.printStackTrace();            throw e;        }finally{            HibernateUtil.closeSession();        }    }