MyBatis-resultType

摘要

　　本文针对XML配置和注解配置说明resultType用法

正文

　　下面的例子都用过查询User类实现

查询单条记录返回对象

• XML配置

<?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.example.UserMapper">
    <!--resultType直接写对象的全类名 -->
    <select id="findById" resultType="com.example.User">
        select * from user where id=#{id}
    </select>
</mapper>

• 注解配置

public interface UserMapper{
    @Select("select * from user where id=#{id}")
    User findById(Long id);
}

查询多条记录返回List

• XML配置

<?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.example.UserMapper">
    <!--resultType直接写对象的全类名 -->
    <select id="findList" resultType="com.example.User">
        select * from user
    </select>
</mapper>

• 注解配置

public interface UserMapper{
    @Select("select * from user")
    List<User> findList();
}

查询单条记录返回Map

　　在没有查询结果没有实体类的情况，我会使用这种方式。

• XML配置

<?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.example.UserMapper">
    <!--resultType直接写对象的全类名 -->
    <select id="findById" resultType="map">
        select * from user where id=#{id}
    </select>
</mapper>

• 注解配置

public interface UserMapper{
    @Select("select * from user where id=#{id}")
    Map<String,Object> findById(Long id);
}

查询多条记录返回Map

　　对部分列需要处理时，我会使用这种方式

• XML配置

<?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.example.UserMapper">
    <!--resultType直接写对象的全类名 -->
    <select id="findMap" resultType="com.example.User">
        select * from user
    </select>
</mapper>

public interface UserMapper{
    // 通过@MapKey注解指定作为key的列名
    @MapKey("id")
    Map<Long,User> findMap();
}

• 注解配置

public interface UserMapper{
    @MapKey("id")
    @Select("select * from user")
    Map<Long,User> findMap();
}