mybatis入门(只包括查询)

mybatis核心配置文件添加

启用驼峰命名,将字段的下划线转换成驼峰模式

<settings>
    <setting name="mapUnderscoreToCamelCase" value="true"/>
</settings>

案例

接口

public interface NameDao {
    Name getNameById(int id);
    List<Name> listNames();
    long countName();
    Map<String,Object> mapName(int id);
    List<Map<String,Object>> mapNames();
    Name getNameByName(@Param("id") int id,@Param("name") String name);
}

配置文件

<?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">
<!-- namespace指定接口的完整类名 -->
<mapper namespace="top.lldwb.mybatis.dao.NameDao">
    <!-- resultType返回类型 -->
    <select id="getNameById" resultType="name" parameterType="int">
        select id, name
        from name
        where id = #{id}
    </select>

    <!-- 在返回集合时，resultType中输入集合的类型(并不是List<Name>) -->
    <select id="listNames" resultType="name">
        select id, name
        from name
    </select>

    <!-- 返回特定的值 -->
    <select id="countName" resultType="long">
        select count(*)
        from name
    </select>

    <!-- 返回map -->
    <select id="mapName" resultType="map" parameterType="int">
        select id, name
        from name
        where id = #{id}
    </select>

    <!-- 返回List<Map> -->
    <select id="mapNames" resultType="map">
        select id, name
        from name
    </select>

    <!-- 多参数查询 -->
    <select id="getNameByName" resultType="name">
        select id, name
        from name
        where id = #{id}
          and name = #{name}
    </select>
</mapper>

Map案例

<!-- 声明resultMap用于User实体类和user_info的表映射-->
<resultMap id="userMap" type="user">
    <!-- id用于映射主键，property指定实体的字段名，column指定表列的名称 -->
    <id property="userId" column="user_id"/>
    <!-- 其他属性使用result标签来映射-->
    <id property="userName" column="user_name"/>
    <id property="userPassword" column="user_password"/>
    <id property="userMail" column="user_mail"/>
    <id property="userState" column="user_state"/>
    <id property="userKey" column="user_key"/>
</resultMap>

<select id="getUserByName" resultMap="userMap">
    select user_id, user_name, user_password, user_mail, user_state, user_key
        from user
    where user_name = #{name}
</select>