如何使用orderbydescending在linq中查询？

Question

我正在尝试查询数据,其结果是降序.当我查询 -

StartDate=04/09/2014&EndDate=04/16/2014,

我得到的结果显示从9日而不是16日.我不清楚这是如何实现的.这就是我目前拥有的:

 public HttpResponseMessage Get([FromUri] Query query)
    {
            var data = db.data_bd.AsQueryable();

            int pageSize = 10;

            if (query.price_type != null)
            {
                data = data.Where(c => c.Cover == query.price_type);
            }
            if (query.endDate != null)
            {
                data = data.Where(c => c.UploadDate <= query.endDate);
            }

            if (query.startDate != null)
            {
                data = data.Where(c => c.UploadDate >= query.startDate);
            }


            // If any other filters are specified, return records which match any of them:
            var filteredData = new List<IQueryable<data_bd>>();

            if (!string.IsNullOrEmpty(query.name))
            {
                var ids = query.name.Split(',');
                foreach (string i in ids)
                {
                    filteredData.Add(data.Where(c => c.Name != null && c.Name.Contains(i)));
                }
            }

            if (filteredData.Count != 0)
            {
                data = filteredData.Aggregate(Queryable.Union);
            }

            if (!data.Any())
            {
                var message = string.Format("No data was found");
                return Request.CreateErrorResponse(HttpStatusCode.NotFound, message);
            }

            if (query.startDate != null)
            {
               data = data.OrderByDescending(c => c.UploadDate >= query.startDate).Take(pageSize);

            }

            if (filteredData.Count != 0)
            {
                data = data.OrderByDescending(d => d.UploadDate).Take(pageSize);
            }

            //return Request.CreateResponse(HttpStatusCode.OK, data);
        }

我错过了什么吗？请指教.

Answer 1

你有点偏离这里.首先,如果您对列表重新排序4次,前3个将是浪费时间.我不确定你的逻辑是什么,所以我会留下它.您需要重新考虑过滤逻辑.

其次,Func你传递的是OrderByDescending获得订购的关键 ; 它不执行过滤.所以当你这样做时:

data = data.OrderByDescending(c => c.UploadDate >= query.startDate)

true如果您的上传日期在查询开始日期之后,并且false在查询开始日期之前,则使用密钥.因此,您将获得所有trues后面的所有falses.你根本不是按日期订购的.

要按日期订购,您需要执行以下操作:

data.Where(c => c.UploadDate >= query.startDate)
    .OrderByDescending(c => c.UploadDate)

这将选择上载日期在查询开始日期之后的所有项目,然后按顺序排序UploadDate.

我的建议是首先使用你的每个过滤器Where,然后通过做OrderByDescending(c => c.UploadDate)(或你打算订购的任何财产)最后做你的订购.