mybatis_SQL映射(1)

文章摘录自：http://blog.csdn.net/y172158950/article/details/17258377

1. select的映射

<select id="selectPerson" parameterType="int" resultType="hashmap">
       select id, name, sex, updateTime from person where id =#{id};
</select>

a) #{id}：创建预编译语句参数，占位符

b) parameterType：参数的类型，int类型

c)resultType：返回的结果集，封装为hashMap

public Map<String, Object> selectPersonById(int id) {
    SqlSession session = DbFactory.getInstance().openSession();  //单例SqlSessionFactory工厂
    Map<String, Object> m = (Map<String, Object>) session.selectOne("com.yjq.entity.Person.selectPerson", id);
    session.commit();
    session.close();
    return m;
}

//output
{id=4, sex=f, NAME=zql, updateTime=2013-12-10 14:18:11.0, SEX=f, name=zql, ID=4, UPDATETIME=2013-12-10 14:18:11.0}

d) 结果集为啥有大小写的key2份？神奇的mybatis啊。

2. insert,update,delete的映射

<insert id="insertPerson" parameterType="com.yjq.entity.Person" useGeneratedKeys="true" keyProperty="id"> <!-- 将自增主键生成的值回写到对象  -->
       insert into person(name, sex, updateTime) values(#{name}, #{sex}, #{updateTime});
</insert>
<delete id="deletePerson" parameterType="int">
       delete from person where id=#{id};
</delete>
<update id="updatePerson" parameterType="com.yjq.entity.Person">
       update person set name=#{name}, sex=#{sex}, updateTime=#{updateTime} where id=#{id};
</update>

a) parameterType="com.yjq.entity.Person"：对象参数，#{name}表示Person对象的name属性。

b) useGeneratedKeys="true" keyProperty="id"：只存在于insert命令，写这2个参数会将主键自增长的值回写到传入的参数对象。

public Person insertPerson(Person p) {
    SqlSession session = DbFactory.getInstance().openSession();
    session.insert("com.yjq.entity.Person.insertPerson", p);
    session.commit();
    session.close();
    return p;
}

PersonDao dao = new PersonDao();
Person p = new Person();
p.setName("zql");
p.setSex("f");
p.setUpdateTime(new Date());
System.out.println("------" + p.getId());
dao.insertPerson(p);
System.out.println(p.getId());

//output（insert前id未赋值，insert后id=7）
------0
7

c) 返回值：insert，update，delete方法均返回int参数，表示操作了多少条数据

int result = session.update("com.yjq.entity.Person.updatePerson", p);

d) 假设数据库不支持自增id，mybatis可以生成随机主键

<insert id="insertPerson2" parameterType="com.yjq.entity.Person">
    <selectKey keyProperty="id" resultType="int" order="BEFORE">  <!-- 生成随机id数 -->
        select CONVERT(RAND()*1000000,SIGNED) a from dual;
    </selectKey>
    insert into person(id, name, sex, updateTime) values(#{id}, #{name}, #{sex}, #{updateTime});
</insert>