mybatis 的mapper 實現

在項目里面，我們經常用到mybatis，多年前的hibernate已經慢慢被大家所拋棄。自從iteye被收購以后，好久沒有寫博客了，今年是要多寫一些補一補。今天來聊一下mybatis的mapper實現。

   @Component

public interface ActivityMapper {
/**

• 添加獎品記錄
• @param prizeEntity
• @return
  */
  int addGift(PrizeEntity prizeEntity);

/**
 * 添加預約記錄
 * @param activityPrevueEntity
 * @return
 */
int addActivityPrevue(ActivityPrevueEntity activityPrevueEntity);

/**
 * 根據手機號和活動id獲取該用戶是否預約過
 * @param phone
 * @param activityId
 * @return
 */
int countPrevueByPhoneAndActivityId(@Param("phone")String phone, @Param("activityId")Integer activityId);

}

這是一個比較常見的mapper類的寫法。在xml里面我們需要定義一個和方法名一樣的id.

<?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.vcinema.mapper.ActivityMapper">

<insert id="addGift" parameterType="cn.vcinema.model.PrizeEntity">
    insert into pumpkin_ius.activity_prize_record(user_id, activity_id, prize_code, create_time)
    values(#{userIdInt}, #{activityIdInt}, #{prizeCodeStr}, now())
</insert>

<insert id="addActivityPrevue" parameterType="cn.vcinema.model.ActivityPrevueEntity">
    insert into pumpkin_ius.activity_user_enroll(activity_id, user_id, user_phone, user_name, user_email, create_time)
    values(#{activityId}, #{userId}, #{userPhone}, #{userName}, #{userEmail}, now())
</insert>

<select id="countPrevueByPhoneAndActivityId" resultType="java.lang.Integer">
    select count(*) from pumpkin_ius.activity_user_enroll where user_phone = #{phone} and activity_id = #{activityId}
</select>

</mapper>

在serviceimpl里面，我們通過調用mapper就可以實現xml 的sql執行。

Gift gift = Lottery.lottery(giftList, defaultGift.get(0));
PrizeEntity prizeEntity = setPrizeValue(gift, user.getUserId(), activityId);
// 添加抽獎記錄
activityMapper.addGift(prizeEntity);

需要給MyBatis提供Mapper接口和與之匹配的映射文件,就能夠讓MyBatis按照我們的需求執行到對應的SQL 這里的實現原理就動態代理

public class MapperProxy<T> implements InvocationHandler, Serializable {
private static final long serialVersionUID = -6424540398559729838L;
private final SqlSession sqlSession;
private final Class<T> mapperInterface;
private final Map<Method, MapperMethod> methodCache;

public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
}

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if(Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, args);
    } else {
        MapperMethod mapperMethod = this.cachedMapperMethod(method);
        return mapperMethod.execute(this.sqlSession, args);
    }
}

private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method);
    if(mapperMethod == null) {
        mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration());
        this.methodCache.put(method, mapperMethod);
    }

    return mapperMethod;
}

}

在invoke方法中可以看到,如果我們調用的是Object中的方法,不做任何處理,直接調用,否則執行:
mapperMethod.execute(this.sqlSession, args);

這里是用jdk的動態代理來實現了自動調用。

在開發的時候，我們有時候不寫xml ，通過注解的形式直接實現調用，查看例子。

@Component
public interface FeedbackMapper {
int insert(Feedback feedback);

/**
 * 添加用戶意見反饋
 * @param userFeedback
 */
@Insert("  INSERT INTO `pumpkin_ius`.`user_feedback`(`phone`, `device`, `pc_device`, `pc_os`, `pc_channel`, `pc_ip`, `pc_platform`, `pc_version`, `pc_browser_name`, `pc_browser_version`, `play_feedback`, `program_feedback`, `other_feedback`) VALUES (#{phone},#{device},#{pc_device},#{pc_os},#{pc_channel},#{pc_ip},#{pc_platform},#{pc_version},#{pc_browser_name},#{pc_browser_version},#{play_feedback},#{program_feedback},#{other_feedback});")
void addUserFeedback(UserFeedback userFeedback);

}

當然，在SQL復雜的時候，還是寫xml比較方便維護，看起來不那么難受。