Question

型号：

return (from m in meterReadings
       group m by new { date = m.ReadDate } into g
       select new
       {
           ReadDate = g.Key.date.ToString("dd.MM.yyyy - HH:mm:ss"),
           T1 = from t1 in g
                where t1.Name == "T1"
                select t1.Value.ToString("0,0.000"),
           T2 = from t2 in g
                where t2.Name == "T2"
                select t2.Value.ToString("0,0.000"),
           T3 = from t3 in g
                where t3.Name == "T3"
                select t3.Value.ToString("0,0.000"),
           Total = from total in g
                where total.Name == "Toplam"
                select total.Value.ToString("0,0.000")
       }).AsQueryable<object>();

查询

var table = MeterReadingManager.GetMeterReadingsPivot(meterReadings, 1);
//No Error (in title)
rows = table.OrderBy("ReadDate","desc").Skip((pageIndex) * pageSize).Take(pageSize)
//Error  (in title)
rows = table.OrderBy("T1","desc").Skip((pageIndex) * pageSize).Take(pageSize)

当我通过ReadDate订购时，它有效。但是当我尝试按其他字段排序时，我收到错误：At least one object must implement IComparable

为什么我收到此错误？我该如何解决？

Answer 1

如果要对任何类型的项目列表进行排序，则类型必须实现IComparable才能使排序算法能够比较项目。 T1是IQueryable，没有实现IComparable。我认为你打算为T1，T2和T3创建字符串值。如果是这样，您应该为每个创建T1等的linq语句添加FirstOrDefault()

修改

（评论后）

我的意思是：

T1 = (from t1 in g where t1.Name == "T1" select t1.Value.ToString("0,0.000")).FirstOrDefault()

现在T1是一个字符串，因此可以用于排序。

Answer 2

您可以尝试ThenByDescending：

var rows = table
    .OrderByDescending(x => x.ReadDate).Skip((pageIndex) * pageSize).Take(pageSize)
    .ThenByDescending(x => x.T1).Skip((pageIndex) * pageSize).Take(pageSize);

<强>更新：如果按一个字段排序，你可以使用Reflection（慢一点）：

var tableInfo = table.GetType().GetProperty("T1"); 
var sortedRow = table.OrderByDescending(x => tableInfo.GetValue(x, null)).Skip((pageIndex) * pageSize).Take(pageSize);

至少有一个对象必须实现IComparable？

2 个答案: