c# - 检查 LINQ 查询是否返回行

Question

我需要检查查询是否返回行，如果返回，则将其更改为字符串，如果没有，则返回“In Progress”。我认为下面的代码可以工作，但事实总是如此:

if (System.Linq.Enumerable.Count(columns) == 0)<--- always true but it shouldn't be

当没有行返回到列时，我在 jQuery Ajax 中收到以下错误:“转换为值类型\u0027Int32\u0027 失败，因为物化值为 null。结果类型\u0027s 泛型参数或查询必须使用可为 null 的类型。”

这是我的网络方法:

using (dbPSREntities5 myEntities = new dbPSREntities5())
    {
        var thisId = myEntities.tbBreadCrumbs.Where(x => x.ProjectID == projectID && x.StatusID == statusID).Max(x => x.BreadCrumbID);
        var columns = myEntities.tbBreadCrumbs
            .Where(x => x.BreadCrumbID == thisId)
            .Select(x => x.CreateDateTime)
            .ToList();

        if (System.Linq.Enumerable.Count(columns) == 0)
        {
            var formattedList = columns
                .Select(d => null != d
                    ? d.Value.ToString("MMM dd, yyyy")
                    : string.Empty) // this is just one example to handle null
                .ToList();

            return formattedList;<-- return this if there is a BreadCrumbID (columns would have a row)
        }
        else
        {
            return "In Progress";<--- there was no BreadCrumbID (columns would have 0 rows)
        }

    }

Answer 1

你可以使用Any()

MSDN Enumerable.Any Method