Question

我想做以下

var totalNoOfRows = result.First().TotalNumberOfCount;

最后做那样的事情

bookssList.AddRange(retResult.Select(r => r.ToBook()));

其中ToBook是扩展方法

但我总是得到查询的结果不能多次枚举。

if (result != null)
                            {

    var totalNoOfRows = result.First().TotalNumberOfCount;
                                pagingContext.ItemsTotal = totalNoOfRows != null ? int.Parse(totalNoOfRows.ToString()) : 0;
                                var retResult = result.ToList();
                               // pagingContext.ItemsTotal = totalcount.Value != null ? int.Parse(totalcount.Value.ToString()) : 0;
                                                                    bookssList.AddRange(retResult.Select(r => r.ToBook()));
                            }

Answer 1

很难猜测你在做什么，以及这些片段如何相互关联，但如果你只能枚举一次，那么先调用ToArray：

var resultCopy = result.ToArray();

//... any number of operations on resultCopy

请注意，调用First也算作枚举。因此，您需要在此之前枚举和复制集合。

Answer 2

尝试将代码更改为此代码，因此您只需枚举result一次：

var retResult = result.ToList();
var totalNoOfRows = retResult.First().TotalNumberOfCount;  //You are now using LINQ on the list, not the query!
pagingContext.ItemsTotal = totalNoOfRows != null ? int.Parse(totalNoOfRows.ToString()) : 0;
                               // pagingContext.ItemsTotal = totalcount.Value != null ? int.Parse(totalcount.Value.ToString()) : 0;
Logger.LogInfo("Search Payments GetPaymentsWithCount stored procedure result not null and count=" + totalcount);
bookssList.AddRange(retResult.Select(r => r.ToBook()));

查询不能多次枚举

2 个答案: