VB.Net and handling dates within Grid Controls - better way? - vb.net

Question

While I have my app running, I question the methodology, and wondering if there’s a “better way”…
Overall design is to allow editing 200-300 records from a gridview (phase1) using VB.Net. The database itself is on SQL Server. There are a number of columns a user will enter into an “application”, and there are several columns that will be edited/maintained by “office users”, if you will. There are several dates involved in this ongoing maintenance, and that’s where the first of my questions revolves.
I have found “solutions” on the internet that got the code working, but am questioning them…
Problem #1 I ran into – dates are NULL in the database, and in trying to read them in using a SqlDataReader led to errors (cannot assign NULL to a Date object). Ok, that led into using a ternary operator to use “IsDBNull”, and either assign the value read from the DB, or to assign DateTime.MinValue. Problem “solved”…
Problem #2 – using the above method now shows dates that are the minimum VB date value – showing actual dates in the fields the user is to edit – definitely not “user friendly”, nor what I want. The only solution to this issue was:
Convert dates from Date or DateTime objects into String objects. This would then allow me to be able to assign an empty string to the gridview in the case where the date was originally NULL in the DB, which had to be transformed into DateTime.MinValue (which could be tested), and then another ternary operator to assign either “ToString” conversion, or an empty string to the gridview field.
Ok – editing is now accomplished. I added some “ScriptManager.RegisterStartupScript” commands to allow testing the validity of the dates the user enters – all is well.
Problem #3 (or 4) – I now need to update the database with the data the user entered – PRESERVING THE EMPTY DATE STRINGS – and update the database (using parameters…) with NULLs back in those date columns. However, again – the date is a string, and is empty, so I had to assign to a “MinValue”, first, then another ternary operator to test each date against “MinValue”, and either assign the date, or a DBNull.Value…
Yes, I guess I could have come up with a number of different update strings (including dates in some, excluding in others), depending on whether or not a string/date was empty or not... But that will only lead to future bugs, so, I guess I’ll be keeping a series of ternary operators.
So, the code for beginning the edit process looks something like:
While sdr.Read
Dim _date1 As Date = If(IsDBNull(sdr("date1")), DateTime.MinValue, sdr("date1"))
.
.
.
‘ Now add them to a List of my Class:
appsList.Add(New AppClass(… _
If(_date1 = DateTime.MinValue, " ", _date1.ToString("MM/dd/yyyy")), _
… )
Now to get the data back from the gridview to update the database:
Dim _date1 As Date
' see if we can convert the various dates...
Try
' see if empty…
If ((CType((row.Cells(19).Controls(0)), TextBox)).Text).Length < 2 Then
_date1 = DateTime.MinValue
Else
_date1 = DateTime.Parse((CType((row.Cells(19).Controls(0)), TextBox)).Text)
End If
Catch ex As Exception
ErrFlag = True
ScriptManager.RegisterStartupScript(Me, Page.GetType, "Script", "alert(‘Date1 Date is not valid - enter as MM/DD/YYYY');", True)
End Try
.
.
.
Dim sql As String = "UPDATE [foo_bar].[dbo].[bar_foo] set date1=#Date1, …….)
cmd.Parameters.AddWithValue("#Date1", If(_date1 = DateTime.MinValue, DBNull.Value, _date1))
Honestly, all this conversion back and forth seems like it’s going to lead to bugs or errors at some point.
So – is this the “best” method for handling this? There isn’t a cleaner way?

Answer 1

If your using winforms then you can handle the Format and parse of the databindings. I haven't tried it on a Gridviewtextbox but worst case you can use a custom cell template and a textbox with format and parse handlers. The code would be something like this:
mybinding = New Binding("text", DataSet1, "table1.datefield")
Me.DataGridTextBoxColumn1.TextBox.DataBindings.Add(mybinding)
AddHandler mybinding.Parse, AddressOf StringToDateTime
AddHandler mybinding.Format, AddressOf formatdate
Private Sub StringToDateTime(ByVal sender As Object, ByVal cevent As ConvertEventArgs)
If cevent.Value.GetType().Equals(GetType(String)) And _
cevent.DesiredType Is GetType(DateTime) Then
If cevent.Value <> "" Then
' Make sure matches format in format funtion
cevent.Value = DateTime.Parse(String.Format(cevent.Value, "MMM d, yy"))
Else
cevent.Value = DBNull.Value
End If
'cevent.Value = DateTime.Parse(String.Format(cevent.Value, "MMM d yyyy")
End If
End Sub
Public Sub formatdate(ByVal sender As Object, ByVal e As ConvertEventArgs)
If e.Value.GetType().Equals(GetType(DateTime)) And e.DesiredType Is GetType(String) Then
' Hard-coded or user-specified
' Make sure matches format in parse funtion
e.Value = Format(e.Value, "d")
End If
End Sub