引數傳遞

單個字面量型別的引數

在mapper介面中使用單個引數,直接使用#{}或者${}在對映檔案中接收,注意${}本質是字串拼接,因此在接收字元型的資料使用單引號括起來,#{}本質為預留位置.

eg:

mapper介面:

package com.mappers;
import com.pojo.User;

public interface UserMapper {

   User selectUserById(int userid);
   User selectUserByName(String username);

}

對映檔案:

<?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">
<!--第一個一致,對應Mapper介面-->
<mapper namespace="com.mappers.UserMapper">

    <!--第二個一致,對應方法名    User selectUserById(int userid); -->
  <select id="selectUserById" resultType="user">
        select * from user where userid=#{userid}
  </select>

    <!--User selectUserByName(String username);-->
    <select id="selectUserByName" resultType="User">
        select * from user where username='${username}'
    </select>
<!--     select * from user where username=#{username}-->


</mapper>

呼叫方法時直接傳參:

selectUserByName("張三");

selectUserById(2);

介面方法引數有多個

這時系統會將引數放入Map集合中,以兩種方式進行儲存

1. 以arg0,arg1....為鍵,傳入的引數為值
2. 以param1,param2...為鍵,傳入的引數為值

因此在對映檔案中存取可以通過#{}或者${}寫入對應鍵進行存取

mapper介面:

package com.mappers;
import com.pojo.User;

public interface UserMapper {

   User selectUserByIdAndName(int userid,String username);

}

對映檔案:

 <!-- User selectUserByIdAndName(int userid,String username);-->
    <select id="selectUserByIdAndName" resultType="User">
        select * from user where userid=#{arg0} and username=#{arg1}
       <!--或者 select * from user where userid=#{param1} and username=#{param2}-->
    </select>

方式2:

使用map作為引數進行傳遞多個引數

mapper介面:

package com.mappers;
import com.pojo.User;


import java.util.Map;

public interface UserMapper {

   User selectUserByIdAndName(Map<String, Object> map);

}

對映檔案:

 <select id="selectUserByIdAndName" resultType="User">
        select * from user where userid=#{userid} and username=#{username}
    </select>

呼叫:先定義好map,再進行呼叫

    Map<String,Object> map=new HashMap<>();
        map.put("userid",2);
        map.put("username","李四");
       User user3=userMapper.selectUserByIdAndName(map);

方式3:(推薦)

使用@Param("")註解,本質也是放到Map集合裡,知識我們規定了鍵名,在使用時直接通過指定的鍵名存取,在註解的引數裡寫入我們指定的鍵名

mapper介面:

package com.mappers;
import com.pojo.User;

public interface UserMapper {

  User selectUserByIdAndName(@Param("userid") int userid, @Param("username") String username);

}

對映檔案:

    <select id="selectUserByIdAndName" resultType="User">
        select * from user where userid=#{userid} and username=#{username}
    </select>

傳入引數為實體類物件

直接通過#{}或${}和屬性名對各個屬性值進行使用

mapper介面

package com.mappers;
import com.pojo.User;

public interface UserMapper {

int insertUser(User user);

}

對映檔案:使用時通過類內屬性名即可存取

<!--    int insertUser(User user);-->
    <insert id="insertUser">
        insert into user values (null,#{username},#{userpass},#{usertel},#{usercard});
    </insert>

呼叫:先定義,然後傳入使用

User user4=new User(1,"哈哈","aiw","159",10);
userMapper.insertUser(user4);