Question

Hoping for a quick answer here.

OK, since I do a lot of single value lookups from the DB, I created a function to handle the lookup for me. It’s designed to get any type of data type (string, integer, date, …).

It works when I want to retrieve a number, but gives me an error when I want a string (InvalidCastException trying to convert a string to an integer on the line: GetValue = DR(0)).
I can’t do a ctype or directcast because the datatype is unknown and varies.
Haven’t tested any other data types yet.

Code is below. I’d like to find out how to make this function work, or pointed to another function that will serve the same purpose.

Public Shared Function GetValue(Optional ByVal SQL As String = "", Optional ByVal FieldName As String = "", Optional ByVal TableName As String = "", Optional ByVal WhereClause As String = "") As VariantType?
    Dim myConnection As SqlConnection
    Dim myCommand As SqlCommand
    Dim strSQL As New SQLStringBuilder
    Dim DR As SqlDataReader

    myConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("ConnAFRAMSSQL").ConnectionString)
    strSQL.Add(SQL)
    If FieldName > "" Then
        strSQL.Add("SELECT " & FieldName)
    End If
    If TableName > "" Then
        strSQL.Add("FROM " & TableName)
    End If
    If WhereClause > "" Then
        strSQL.Add("WHERE " & WhereClause)
    End If
    myConnection.Open()
    myCommand = New SqlCommand(strSQL.ToString, myConnection)
    DR = myCommand.ExecuteReader()
    If DR.HasRows Then
        DR.Read()
        GetValue = DR(0)
    Else
        GetValue = Nothing
    End If
End Function

Thanks.

Answer 1

You may specify the System.Object (System.Object is the ultimate base class of all types) return type of your method.

Public Shared Function GetValue(Optional ByVal SQL As String = "", Optional ByVal FieldName As String = "", Optional ByVal TableName As String = "", Optional ByVal WhereClause As String = "") As Object
    Dim myConnection As SqlConnection
    ....
   Dim obj as Object=Nothing
   If DR.Read()
        obj=DR(0)
   End If
   DR.Close()
   myConnection.Close()
   return obj
End Function