Mybatis输入映射与输出映射，动态SQL

Mybatis输入映射和输出映射

Mybatis支持输入映射哪些类型

简单类型、POJO（自定义类型），HashMap

POJO的包装的类型，就是类中还有其他类的对象

就是parameterType支持的输入映射的类型

<?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="com.hyx2.dao_two.mapper.UserMapper">

<select id="findUserById" parameterType="int" resultType="pojo.User">
        select  * from user where id = #{id}
    </select>

</mapper>

输出映射

resultType

（1）支持的类型

         基本类型、pojo、hashMap

（2）输出是POJO和POJO列表问题

不管是输出是单个POJO，还是POJO列表，在Mapper.xml中resultType都是一样的，只是在Mapper接口中返回值类型不一样。

（3）使用条件

使用resultType进行输出映射的时候，只要查询出来的列名和POJO的属性名一致，该列才可以映射成功。

         只要查询出来的列名和属性名有一个能对应的上，就会创建POJO对象。

         如果查询出来的列名和属性名没有一个能对应上，就不会创建POJO对象。

vo与po

po使用在持久层

vo使用在视图层，也就是使用mvc时向view中传入数据的模型

案例实现：

项目结构

UserMapper

import pojo.User;
import vo.UserQueryVo;

import java.util.List;

public interface UserMapper {
    /**
     * 找到用户
     */
    public List<User> findUserList(UserQueryVo userQueryVo);
}

 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">
<mapper namespace="com.hyx2.vo_resulttype.mapper.UserMapper">

    <select id="findUserList" parameterType="vo.UserQueryVo"
            resultType="pojo.User">
        select  * from user where username like "%"#{user.username}"%" and sex = #{user.sex}
    </select>
</mapper>

UserQueryVo

package vo;

import pojo.User;

public class UserQueryVo {
    //用户信息
    private User user;


    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}

User，有一个数据库，数据库中有User表，表列的属性对于User类的属性

package pojo;

import java.util.Date;

public class User {
    private Integer id;
    private String username;// 用户姓名
    private String sex;// 性别
    private Date birthday;// 生日
    private String address;// 地址

    public User() {
    }

    public User(String username, String sex, Date birthday, String address) {
        this.username = username;
        this.sex = sex;
        this.birthday = birthday;
        this.address = address;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" + "id=" + id + ", username='" + username + '\'' + ", sex='" + sex + '\'' + ", birthday=" + birthday + ", address='" + address + '\'' + '}';
    }
}

在sqlMapconfig中配置UserMapper.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">
<configuration>

    <properties resource="db.properties"></properties>


    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <!--数据库连接要素，数据库，数据库位置，账户，密码-->
                <property name="driver" value="${jdbc.driver}"></property>
                <property name="url" value="${jdbc.url}"></property>
                <property name="username" value="${jdbc.username}"></property>
                <property name="password" value="${jdbc.password}"></property>
            </dataSource>
        </environment>
    </environments>

    <!--配置实体类的xml文件，在这文件中执行sql语句-->
    <mappers>
      
        <package name="mapper"></package>

    </mappers>
</configuration>

 db.properties数据库配置文件

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis01?characterEncoding=UTF-8
jdbc.username=root
jdbc.password=123

测试代码：

package test;

import mapper.UserMapper;
import pojo.User;
import vo.UserQueryVo;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Dmo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream( "sqlMapconfig.xml" );
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }

    @Test
    public void fun(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        //获取UserMapper.class，通过反射机制可以找到UserMapper.xml文件
        UserMapper userMapper = sqlSession.getMapper( UserMapper.class );
        UserQueryVo userQueryVo = new UserQueryVo();
        User user = new User();
        user.setUsername( "小" );
        user.setSex( "1" );
        userQueryVo.setUser( user );

        List<User> userList = userMapper.findUserList( userQueryVo );
        for (User u : userList) {
            System.out.println(u);
        }

    }
}

resultMap

        使用条件

         Mybatis使用resultMap完成高级输出结果映射

         当列名和属性名不一致的情况，自己来指定如何进行映射

案例只需修改resultType中的案例中的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">
<mapper namespace="com.hyx2.vo_resultmap.mapper.UserMapper">
    
    <!--
        resultMap作用：告诉人家，列和属性怎么建立关系
        id:给一个唯一的标识
        type：通过指定映射，映射成目标对象
       -->
    <resultMap id="userResultMap" type="pojo.User">
        <!-- column:列，表的列，property：POJO中属性 -->
        <id column="uid" property="id"></id>
        <result column="uname" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>
    </resultMap>

    <select id="findUserList" parameterType="vo.UserQueryVo"
            resultMap="userResultMap">
              select  id as uid,username as uname,birthday ,sex ,address  from user where username
		like "%"#{user.username}"%" and sex = #{user.sex}
    </select>
</mapper>

动态SQL

需求（1）：更新用户，前端修改了什么，SQL语句就包含哪些列

Update user set username=? where uid = ?

Update user set username=?,sex=? where uid = ?

Java 代码进行判断。

If(username ==null){

         拼接SQL语句

}

需求（2）：根据用户名和性别查询用户列表，

如果传递了用户名和性别，2个都作为条件

如果传递了用户名，没有传递性别，用户名作为条件

一个参数都没有传递，就没有条件

为了更好的解决上述需求，可以使用动态SQL进行实现

案例只需修改resultMap中的案例中的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">
<mapper namespace="mapper.UserMapper">

    <!--
        resultMap作用：告诉人家，列和属性怎么建立关系
        id:给一个唯一的标识
        type：通过指定映射，映射成目标对象
       -->
    <resultMap id="userResultMap" type="pojo.User">
        <!-- column:列，表的列，property：POJO中属性 -->
        <id column="uid" property="id"></id>
        <result column="uname" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>
    </resultMap>


    <select id="findUserList" parameterType="vo.UserQueryVo"
            resultMap="userResultMap">
              select  id as uid,username as uname,birthday ,sex ,address
              from user
             <where>
                 <if test="user.username!=null and user.username!=''">
                     and username like "%"#{user.username}"%"
                 </if>
                 <if test="user.sex!=null and user.sex!=''">
                     and sex = #{user.sex}
                 </if>
             </where>
    </select>
</mapper>

测试代码如下：

import mapper.UserMapper;
import pojo.User;
import vo.UserQueryVo;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Dmo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream( "result_map_sqlMapconfig.xml" );
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }

    @Test
    public void fun(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper( UserMapper.class );
        UserQueryVo userQueryVo = new UserQueryVo();

        User user = new User();
        user.setUsername( "王" );
        userQueryVo.setUser( user );

        List<User> userList = userMapper.findUserList( userQueryVo );
        for (User u : userList) {
            System.out.println(u);
        }

    }
}

SQL 片段，实现代码重用

<?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="mapper.UserMapper">


    <!--
        resultMap作用：告诉人家，列和属性怎么建立关系
        id:给一个唯一的标识
        type：通过指定映射，映射成目标对象
       -->

    <sql id="query_user_where">
        <if test="user.username!=null and user.username!=''">
            and username like "%"#{user.username}"%"
        </if>
        <if test="user.sex!=null and user.sex!=''">
            and sex = #{user.sex}
        </if>
    </sql>
    <resultMap id="userResultMap" type="pojo.User">
        <!-- column:列，表的列，property：POJO中属性 -->
        <id column="uid" property="id"></id>
        <result column="uname" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>
    </resultMap>


    <select id="findUserList" parameterType="vo.UserQueryVo"
            resultMap="userResultMap">
              select  id as uid,username as uname,birthday ,sex ,address
              from user
             <where>
                 <include refid="query_user_where"></include>
             </where>
    </select>
</mapper>
 

Foreach

案例：

先为上述案例中的UserMapper.class添加一个方法

package mapper;

import pojo.User;
import vo.UserQueryVo;

import java.util.List;

public interface UserMapper {
  
    /**
     * 找打用户在一定的范围内
     * @param userQueryVo
     * @return
     */

    public  List<User> findUserListByIds(UserQueryVo userQueryVo);
}

再写UserMapper.xml文件

<?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="mapper.UserMapper">

    <!--
        resultMap作用：告诉人家，列和属性怎么建立关系
        id:给一个唯一的标识
        type：通过指定映射，映射成目标对象
       -->
    <resultMap id="userResultMap" type="pojo.User">
        <!-- column:列，表的列，property：POJO中属性 -->
        <id column="uid" property="id"></id>
        <result column="uname" property="username"></result>
        <result column="birthday" property="birthday"></result>
        <result column="sex" property="sex"></result>
        <result column="address" property="address"></result>
    </resultMap>


    <select id="findUserListByIds" parameterType="vo.UserQueryVo"
            resultMap="userResultMap">
        select  id as uid,username as uname,birthday ,sex ,address from user

        <where>
            <if test="ids!=null">

                <foreach collection="ids" open="id in (" separator="," close=")" item="userId">
                    #{userId}
                </foreach>
            </if>
        </where>
    </select>
</mapper>

 再为UserQueryVo.class添加一个新属性

package com.hyx2.vo_resultmap.vo;

import com.hyx2.vo_resultmap.pojo.User;

import java.util.ArrayList;
import java.util.List;

public class UserQueryVo {
    //用户信息
    private User user;
    private List<Integer> ids = new ArrayList<Integer>(  );

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    public List<Integer> getIds() {
        return ids;
    }

    public void setIds(List<Integer> ids) {
        this.ids = ids;
    }
}

测试代码

import mapper.UserMapper;
import pojo.User;
import vo.UserQueryVo;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class Dmo01 {
    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void fun0() throws IOException {
        InputStream inputStream = Resources.getResourceAsStream( "result_map_sqlMapconfig.xml" );
        //通过配置创建会话工厂
        sqlSessionFactory = new SqlSessionFactoryBuilder().build( inputStream );
    }

    @Test
    public void fun() throws IOException {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        UserMapper userMapper = sqlSession.getMapper( UserMapper.class );

        UserQueryVo userQueryVo = new UserQueryVo();
        userQueryVo.getIds().add( 1 );
        userQueryVo.getIds().add( 24 );
        userQueryVo.getIds().add( 25 );
        List<User> userList = userMapper.findUserListByIds( userQueryVo );
        for (User u : userList) {
            System.out.println(u);
        }


    }
}