Question

我在以下查询中获取有关mscorlib.dll错误的InvalidOperation，并且在我的生活中无法找出原因。

这是Class I用List填充List（Of）;

Public Class ProjectionPerformance
    Public SymbolId As Long
    Public Name As String
    Public ProjectionDate As String
    Public ActualRange As Double
    Public ProjectedRange As Double
End Class

除了我转换为字符串的日期

之外，这些类型与表中的类型相匹配

以下是LINQ查询的函数

  Public Shared Function GetRangeProjectionPerformance(Optional daysToRetrieve As Integer = 100) As Dictionary(Of Long, List(Of ProjectionPerformance))

    Dim todaysDate As Date = DateTime.Now.Date
    Dim lookbackDate As Date = todaysDate.AddDays(daysToRetrieve * -1)

    Using ctx As New ProjectionsEntities

        Dim query = (From d In ctx.projections
                    Where d.SymbolId <= 42 AndAlso d.Date >= lookbackDate
                    Join t In ctx.symbols On d.SymbolId Equals t.Id
                    Let actualRange = d.ActualHigh - d.ActualLow
                    Let projectedRange = d.HighProjection - d.LowProjection
                    Select New With {
                    d.Date,
                    d.SymbolId,
                    t.Name,
                    projectedRange,
                    actualRange}).GroupBy(Function(o) o.SymbolId).ToDictionary(Function(p) p.Key,
                                Function(x) x.Select(Function(y) New ProjectionPerformance() With {
                                    .SymbolId = y.SymbolId,
                                    .ProjectionDate = y.Date.ToString(),
                                    .Name = y.Name,
                                    .ActualRange = y.actualRange,
                                    .ProjectedRange = y.projectedRange
                                }).ToList())


        Return query
    End Using
End Function

我在LINQ查询的这一部分上得到了这个错误（我假设那部分在VS2013中以绿色突出显示）

 Function(x) x.Select(Function(y) New ProjectionPerformance() With {

我是否必须检索实际字段值并删除Let语句并在Dictionary调用的List函数中执行计算？

Answer 1

根据您的评论，我怀疑问题在于您尝试将空值分配给ProjectionPerformance中的双重属性。如果您按如下方式更改代码，它应该可以工作：

Dim query = (From d In ctx.projections
                Where d.SymbolId <= 42 AndAlso d.Date >= lookbackDate
                Join t In ctx.symbols On d.SymbolId Equals t.Id
                Let actualRange = d.ActualHigh - d.ActualLow
                Let projectedRange = d.HighProjection - d.LowProjection
                Select New With {
                d.Date,
                d.SymbolId,
                t.Name,
                projectedRange,
                actualRange}).GroupBy(Function(o) o.SymbolId).ToDictionary(Function(p) p.Key,
                            Function(x) x.Select(Function(y) New ProjectionPerformance() With {
                                .SymbolId = y.SymbolId,
                                .ProjectionDate = y.Date.ToString(),
                                .Name = y.Name,
                                .ActualRange = If(y.actualRange, 0.0),
                                .ProjectedRange = y.projectedRange
                            }).ToList())

为了在运行程序之前发现此类错误，您应该将OPTION STRICT设置为ON（在项目或文件级别）。

LINQ上的mscorlib错误

1 个答案: