mybatis 使用resultMap实现数据库的操作

resultType:直接表示返回类型

resultMap：对外部resultMap的引用

二者不能同时使用

创建一个实体类Role和User

public class Role {
    private Integer id;
    private String roleCode;
    private String roleName;
  //省略set、get方法

创建User类（在User中有roleId   1对多关系）

public class User {
    private Integer id;
    private String userName;
    private String userCode;
    private String userPassword;
    private Integer roleId;
    private String roleName;
　　//省略set、get方法
    

创建RoleMapper接口

public interface RoleMapper {
    
    public void  add(Role role);
    
    public void update(Role role);
    
    public void delete(Role role);
    
    public List<Role> getRoleList();

}

创建UserMapper接口

//接口的名字和xml的名字一样，这样xml中的namespace就不用改
public interface UserMapper {
    //接口名的方法名一定要和xml中的id名一样
    public int count();
    
    public void add(User user);
    
    public void update(User user);
    
    public void delete(User user);
    
    public List<User> getUserList();
    
    //根据roleid获取用户列表
    public List<User> getUserByRoleId(Role role);
}

创建RoleMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="cn.bdqn.dao.RoleMapper">
    <select id="getRoleList" resultType="Role">
        select * from role
    </select>
    <insert id="add" parameterType="Role">
        insert into role (roleCode,roleName) 
            values (#{roleCode},#{roleName})
    </insert>
    <update id="update" parameterType="Role">
        update role set roleCode=#{roleCode},roleName=#{roleName} where id=#{id}
    </update>
    <delete id="delete" parameterType="Role">
        delete from role where id=#{id}
    </delete>
</mapper>

创建UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!-- 如果我要调用mapper文件，就去拿到namespace+id(方法名)的名字就可以访问 -->
<mapper namespace="cn.bdqn.dao.UserMapper">
    <!-- id要唯一的，一般是下拉类的方法名 -->
    <!-- 返回的是什么类型int -->
    <select id="count" resultType="int">
        select count(1) from user
    </select>
    <!-- 增加 -->
    <insert id="add" parameterType="User">
        insert into user(userCode,userName,userPassword)
            values (#{userCode},#{userName},#{userPassword})
    </insert>
    <!-- 修改 -->
    <update id="update" parameterType="User">
        update user set userCode=#{userCode},userName=#{userName},
        userPassword=#{userPassword} where id=#{id}
    </update>
    <!-- 删除 -->
    <delete id="delete" parameterType="User">
        delete from user where id=#{id}
    </delete>
    <!-- 查询 -->
    <select id="getUserList" resultType="User">
        select * from user
    </select>
</mapper>

加入这个方法用resultMap

 <!-- resultMap中的id随便取，但要保证id唯一就行 -->
    <!-- type指的是后台的javabean的类名 映射到哪里 -->
    <resultMap type="User" id="userMap">
        <!-- 显示的字段 -->
        <result property="id" column="id"/>
        <result property="userCode" column="userCode"/>
        <result property="userName" column="userName"/>
        <result property="roleName" column="roleName"/>
    
    </resultMap>
    <!-- 拿roleID -->
    <select id="getUserByRoleId" parameterType="User" resultMap="userMap">
        select u.*,r.roleName as roleName from user u,role r where u.roleId = r.id and u.roleId=#{id}
    </select>

在mybatis-config.xml中添加<mapper resource="cn/bdqn/dao/RoleMapper.xml"/>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">

<!-- 通过这个配置文件完成mybatis与数据库的连接 -->
<configuration>
    <!-- 引入 jdbc.properties 文件-->
    <properties resource="jdbc.properties"/>
    <!-- alias别名 -->

<!-- 配置mybatis的log实现LOG4J -->
<settings>
        <setting name="logImpl" value="LOG4J" />
</settings>
    <typeAliases>
        <!-- <typeAlias type="cn.bdqn.pojo.User" alias="User"/> -->
        <!-- 用这个比较方便，不用一个一个写。包下的就是他的类名 -->
        <package name="cn.bdqn.pojo"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <!--配置事务管理，采用JDBC的事务管理  -->
            <transactionManager type="JDBC"></transactionManager>
            <!-- POOLED:mybatis自带的数据源，JNDI:基于tomcat的数据源 -->
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    
    <!-- 将mapper文件加入到配置文件中  将来mapper文件很多所以是mappers -->
    <mappers>
        <mapper resource="cn/bdqn/dao/UserMapper.xml"/>
        <mapper resource="cn/bdqn/dao/RoleMapper.xml"/>
    </mappers>
</configuration>

测试

//查询
    @Test
    public void getUserListTest(){
        SqlSession sqlSession = null;
        try {
            List<User> userList = new ArrayList<User>();
            sqlSession = MyBatisUtil.createSqlSession();
            userList = sqlSession.selectList("cn.bdqn.dao.UserMapper.getUserList");
            for(User user:userList){
                logger.debug("user的id==="+user.getId());
            }
        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
            sqlSession.rollback();
        }finally{
            MyBatisUtil.closeSqlSession(sqlSession);
        }
    }