체크하면 날짜에 열 datatable is null

Question

Dim dr As SqlDataReader = cmd.ExecuteReader(CommandBehavior.CloseConnection)
Dim dt As DataTable = New DataTable()
dt.Load(dr)

For Each row As DataRow In dt.Rows

    Dim dob_str As String = ""

    'code to check if row.Field(Of Date)("DOB") is dbnull
    'if not dbnull then dob_str = row.Field(Of Date)("DOB")

Next

어떻게 확인하는 경우 Date 유형 열 각 행에 대해 DataTable 은 비어 있습니까?

나

    If Not row.Field(Of Date)("DOB") = Nothing Then
        dob_str = row.Field(Of Date)("DOB")
    End If

고

    Dim nullCheck As Boolean = IsDBNull(row.Field(Of Date)("DOB"))
    If nullCheck = False Then
        dob_str = row.Field(Of Date)("DOB")
    End If

하지만 그들은 모두 결과 Cannot cast DBNull.Value to type 'System.DateTime'. Please use a nullable type. 중 런타임입니다.

Answer 1

용 널 유형

If row.Field(Of Date?)("DOB") IsNot Nothing Then
    dob_str = row.Field(Of Date)("DOB")
End If

나

If row.Field(Of Date?)("DOB").HasValue Then
    dob_str = row.Field(Of Date)("DOB")
End If

거나 사용 IsNull

If Not row.IsNull("DOB") Then
    dob_str = row.Field(Of Date)("DOB")
End If