附加信息：无法将“System.Int32”类型的对象转换为“System.String”类型。 - VB.NET

Question

我有这个错误，

无法将“System.Int32”类型的对象转换为“System.String”类型。

代码可以运行，但是重建后代码不再运行

我的代码

Private Sub KodePembelian()
    Dim Rd As SqlClient.SqlDataReader
    Dim Cmd As SqlClient.SqlCommand
    Dim bulan As String
    bulan = Format(Now, "MM")
    Dim tahun As String
    tahun = Format(Now, "yy")
    Dim Urutan As String
    Dim Hitung, Cari As String

    Cmd = New SqlClient.SqlCommand("SELECT * FROM BY_PEMBELIANHEADER WHERE NOPEMBELIAN IN " & "(SELECT MAX (NOPEMBELIAN) FROM BY_PEMBELIANHEADER)", MyConn)
    Rd = Cmd.ExecuteReader
    Rd.Read()
    If Not Rd.HasRows Then
        Urutan = "PO/" & bulan & tahun & "/" & "000001"
    Else
        Cari = Microsoft.VisualBasic.Right(Rd.GetString(0), 6)
        If Microsoft.VisualBasic.Left(Rd.GetString(0), 8) <> "PO/" & bulan & tahun & "/" Then
            Urutan = "PO/" & bulan & tahun & "/" & "000001"
        Else
            Hitung = Microsoft.VisualBasic.Right(Rd.GetString(0), 6) + 1
            Urutan = "PO/" & bulan & tahun & "/" & Microsoft.VisualBasic.Right("000000" & Hitung, 6)
        End If
    End If

    Rd.Close()
    txtpo.SelectedText = Urutan
End Sub

Answer 1

已解决，谢谢 alireza 先生，我只是在我的代码中添加 getsqlvalue(0).tostring

 Private Sub KodePembelian()
        Dim Rd As SqlClient.SqlDataReader
        Dim Cmd As SqlClient.SqlCommand
        Dim bulan As String
        bulan = Format(Now, "MM")
        Dim tahun As String
        tahun = Format(Now, "yy")
        Dim Urutan As String
        Dim Hitung, Cari As String

        Cmd = New SqlClient.SqlCommand("SELECT * FROM BY_PEMBELIANHEADER WHERE NOPEMBELIAN IN " & "(SELECT MAX (NOPEMBELIAN) FROM BY_PEMBELIANHEADER)", MyConn)
        Rd = Cmd.ExecuteReader
        Rd.Read()
        If Not Rd.HasRows Then
            Urutan = "PO/" & bulan & tahun & "/" & "000001"
        Else
            Cari = Microsoft.VisualBasic.Right(Rd.GetSqlValue(0).ToString(), 6)
            If Microsoft.VisualBasic.Left(Rd.GetSqlValue(0).ToString(), 8) <> "PO/" & bulan & tahun & "/" Then
                Urutan = "PO/" & bulan & tahun & "/" & "000001"
            Else
                Hitung = Microsoft.VisualBasic.Right(Rd.GetSqlValue(0).ToString(), 6) + 1
                Urutan = "PO/" & bulan & tahun & "/" & Microsoft.VisualBasic.Right("000000" & Hitung, 6)
            End If
        End If

        Rd.Close()
        txtpo.SelectedText = Urutan
    End Sub

Answer 2

可能返回值为空。在调用GetString 方法之前，您必须调用IsDBNull 来检查空值。

这个 sn-p 应该可以解决问题。

    Rd = Cmd.ExecuteReader
    Rd.Read()
    If Not Rd.HasRows Then
        Urutan = "PO/" & bulan & tahun & "/" & "000001"
    Else
        If Rd.IsDBNull(0) Then
            Cari = "default" ' do something if its null
        Else
            Cari =  Microsoft.VisualBasic.Right(Rd.GetSqlValue(0).ToString(), 6)
        End If 

注意：GetString 方法不进行任何转换；因此，检索到的数据必须已经是一个字符串。

sqldatareader.getstring documentation