Question

我的数据类是

public class Data
{
    public DateTime? Date { get; set; }
    public int Count { get; set; } 
}

以下查询

var queryable = db.MemberStats.Where(ms => ms.MemberId == User.Identity.GetUserId())
                .GroupBy(n => TruncateTime(n.Commited))
                .Select(g => new Data()
                    {
                         Date = g.Key,
                         Count = g.Count()
                    }
                ).ToList();

返回

System.NotSupportedException: 'Method 'System.Nullable`1[System.DateTime] 
TruncateTime(System.Nullable`1[System.DateTime])' has no supported translation to SQL.'

这有什么问题？我该如何解决这个问题？

更新如果我在GroupBy（）之前添加ToList（）我有

   at System.Data.Entity.Core.Objects.EntityFunctions.TruncateTime(Nullable`1 dateValue)
   at .Controllers.ChartController.<>c.<Index>b__1_0(MemberStat n) in \Controllers\ChartController.cs:line 30
   at System.Linq.Lookup`2.Create[TSource](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at System.Linq.GroupedEnumerable`3.GetEnumerator()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.SystemCore_EnumerableDebugView`1.get_Items()

Answer 1

你可以试试这个：

var queryable = db.MemberStats.Where(ms => ms.MemberId == User.Identity.GetUserId())
                .GroupBy(n => EntityFunctions.TruncateTime(n.Commited))
                .Select(g => new Data()
                    {
                         Date = g.Key,
                         Count = g.Count()
                    }
                ).ToList();

要使用EntityFunctions.TruncateTime，您需要引用程序集System.Data.Entity，然后使用System.Data.Objects包含;

TruncateTime（System.Nullable`1 [System.DateTime的]）＆＃39;没有受支持的SQL翻译。＆＃39;

1 个答案: