How To assign null values in VB.NET

Question

Hi,

I am not sure why VB makes everything such a pain. I have a fields which stores the date and time in the format required to store in MySQL database

 Dim AppDate As String = String.Empty
      If Not String.IsNullOrEmpty(Me.AppDate.Text.Trim) Then
         AppDate = Format(CDate(Me.AppDate.Text), "yyyy-MM-dd h:mm:ss")
      Else
        //Need to assign a null value to AppDate 
      End If

Now I need to assign the AppDate to NUll like DBNull, but I am not able to do it directly. If I change AppDate to Date then I am not getting the required format.

Any help is appreciated .

Thanks in Advance.

Answer 1

AppDate = Nothing

Answer 2

AppDate = Nothing should work, you could also use DateTime.MinValue and update your business logic to treat it appropriately.

Answer 3

AppDate = DbNull.Value 'does this work?

Answer 4

The string value returned by the DbNull.ToString() method is the empty string (""), which may imply that the string representation of DbNull is the empty string.

Answer 5

the date and time in the format required to store in MySQL database

If you're building a datetime string to save to a database, you're doing it all wrong.

Using the MySql Connector/Net, you should be building your query like this:

Dim sql As String = "UPDATE `MyTable` SET `MyField` = @MyField WHERE `ID` = @MyID"
Using cn As New MySqlconnection("..your connection string here.."), _
      cmd As New SqlCommand(sql, cn)

    cmd.Parameters.Add("@MyField", MySqlDbType.DateTime).Value = MyDateTimeVar ''# NO FORMATTING NEEDED!
    cmd.Parameters.Add("@MyID", MySqlDbType.Int).Value = MyIDIntegerVar

    cn.Open()
    cmd.ExecuteNonQuery()
End Using