controller类：

/**
 * 下单接口
 */
@PostMapping("save")
public JsonData save(@RequestBody VideoOrderRequest videoOrderRequest, HttpServletRequest request){

    Integer userId = (Integer) request.getAttribute("user_id");

    if (userId == null){
        return JsonData.buildError("");
    }
    videoOrderService.save(userId,videoOrderRequest.getVideoId());

    return JsonData.buildSuccess();
}
接口实现类：

@Autowired
private VideoOrderMapper videoOrderMapper;

@Autowired
private VideoMapper videoMapper;


/**
 * 下单成功
 * @param userId
 * @param videoId
 * @return
 */
@Override
public int save(int userId, int videoId) {

    VideoOrder videoOrder = videoOrderMapper.findByUserIdAndVideoIdAndState(userId,videoId,1);

    if(videoOrder!=null){
        return 0;
    }

    Video video = videoMapper.findById(videoId);
    VideoOrder newVideoOrder = new VideoOrder();

    newVideoOrder.setVideoId(videoId);
    newVideoOrder.setVideoImg(video.getCoverImg());
    newVideoOrder.setVideoTitle(video.getTitle());
    newVideoOrder.setUserId(userId);
    newVideoOrder.setTotalFee(video.getPrice());
    newVideoOrder.setOutTradeNo(UUID.randomUUID().toString());
    newVideoOrder.setState(1);
    newVideoOrder.setCreateTime(new Date());

    int row = videoOrderMapper.saveOrder(newVideoOrder);

    return row;
}

mapper：

/**
 * 查询用户是否购买此商品
 * @param userId
 * @param videoId
 * @param state
 * @return
 */
VideoOrder findByUserIdAndVideoIdAndState(@Param("user_id") int userId,@Param("video_id") int videoId,@Param("state") int state);


/**
 * 下单
 * @param videoOrder
 * @return
 */
int saveOrder( VideoOrder videoOrder);

xml文件：

<select id="findByUserIdAndVideoIdAndState" resultType="VideoOrder">

    select * from video_order where user_id = #{user_id} and video_id = #{video_id} and state = #{state}

</select>

<insert id="saveOrder" useGeneratedKeys="true" keyColumn="id" keyProperty="id">
    INSERT INTO video_order ( `out_trade_no`, `state`, `create_time`,`total_fee`,
                               `video_id`, `video_title`, `video_img`, `user_id`)
     VALUES (#{outTradeNo,jdbcType=VARCHAR},#{state, jdbcType=INTEGER},#{createTime,jdbcType=TIMESTAMP},
             #{totalFee,jdbcType=INTEGER},#{videoId,jdbcType=INTEGER},#{videoTitle,jdbcType=VARCHAR},
             #{videoImg,jdbcType=VARCHAR},#{userId,jdbcType=INTEGER})
</insert>


大家学习加油！