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私はJOIN2つのDataTalesを使用しています（2つのExcelスプレッドシートを解析することで入力されます）。これらのExcelスプレッドシートには列が含まれており、常に値があるTOTAL_DOLLARSとTOTAL_UNITSは限りません。このため、実行しようとすると、プログラムが次のエラーをスローします。query.CopyToDataTable()

DataSet does not support System.Nullable<>

Dim query = From c In dtDollars.AsEnumerable() _
   Join r In dtUnits.AsEnumerable() _
   On c.Field(Of String)("UPC") Equals r.Field(Of String)("UPC") _
   Select _
   New _
   With {.UPC = r.Field(Of String)("UPC"), .WIC_NUMBER = c.Field(Of String)("WIC_NUMBER"), _
   .WAG_ITEM_DESC = c.Field(Of String)("WAG_ITEM_DESC"), _
   .WAG_BRAND = c.Field(Of String)("WAG_BRAND"), .UOM = c.Field(Of String)("UOM"), _
   .GSK_PROMO_GRP = c.Field(Of String)("GSK_PROMO_GRP"), _
   .TOTAL_DOLLARS = c.Field(Of Decimal?)("TOTAL_DOLLARS"), _
   .TOTAL_UNITS = r.Field(Of Integer?)("TOTAL_UNITS"), _
   .WKND_DATE = c.Field(Of DateTime)("WKND_DATE")}

    myResultTable = query.CopyToDataTable()

これを解決するにはどうすればよいですか？=の場合、これらの列のデフォルト値を0に設定する方法はありますDBNull.Valueか？

これがModulesとExtensions私がCopyToDataTable()メソッドに使用しているものです：

Public Module CustomLINQtoDataSetMethods
    <Extension()> _
    Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T)) As DataTable
        Return New ObjectShredder(Of T)().Shred(source, Nothing, Nothing)
    End Function

    <Extension()> _
    Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
        Return New ObjectShredder(Of T)().Shred(source, table, options)
    End Function

End Module

Module DataSetLinqOperators
  ''' <summary>
  ''' Creates a <see cref="DataTable"/> that contains the data from a source sequence.
  ''' </summary>
  ''' <remarks>
  ''' The initial schema of the DataTable is based on schema of the type T. All public property and fields are turned into DataColumns.
  ''' If the source sequence contains a sub-type of T, the table is automatically expanded for any addition public properties or fields.
  ''' </remarks>
  <Extension()> _
  Public Function ToDataTable(Of T)(ByVal source As IEnumerable(Of T)) As DataTable
    Return New ObjectShredder(Of T)().Shred(source, Nothing, Nothing)
  End Function

  ''' <summary>
  ''' Loads the data from a source sequence into an existing <see cref="DataTable"/>.
  ''' </summary>
  ''' <remarks>
  ''' The schema of <paramref name="table" /> must be consistent with the schema of the type T (all public property and fields are mapped to DataColumns).
  ''' If the source sequence contains a sub-type of T, the table is automatically expanded for any addition public properties or fields.
  ''' </remarks>
  <Extension()> _
  Public Function LoadSequence(Of T)(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As System.Nullable(Of LoadOption)) As DataTable
    If table Is Nothing Then
      Throw New ArgumentNullException("table")
    End If
    Return New ObjectShredder(Of T)().Shred(source, table, options)
  End Function
End Module

さらに、ObjectShredderクラスを使用しています。

どんな助けでも大歓迎です！

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1 に答える 1

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これを試して：

.TOTAL_DOLLARS = If( (c.Field(Of Decimal?)("TOTAL_DOLLARS")).HasValue, _
                     (c.Field(Of Decimal?)("TOTAL_DOLLARS"), 0))

少し厄介ですが、うまくいくはずです。

于 2012-12-21T22:47:09.657 に答える