How to skip DateTime conversion? - vb.net

Question

in VB.NET I have TextBox with masked time input such as
__:__
Before I save this to SQL database I have a conversion to iso format like:
Dim MyTime As DateTime = DateTime.ParseExact(txtMyTime.Text, "HH:mm", Nothing)
Dim isoMyTime As String = MyTime.ToString("HH:mm:ss")
Now my question is how to write to database Null value if this text box is empty without time value input?

Answer 1

not sure if you are stuck on SQL, or to figure out wether the textbox has been given a value.
when you write to database, you define the columns that you want to write to:
insert into Table1(Forename, Surname)
values(John, Jehnson)
if you want the surname to be null, simply do not mention it:
insert into Table1(Forename)
values(John)
Make sure your column is designed to allow nulls.
to figure out if the textbox has a value, simply Check if the values matches a actual valid format
solution 1
you can achieve this with a Regex:
[0-9]{2}:[0-9]{2}
this regex makes sure that there are 2 numbers before and after the : sign.
solution 2
You can also replace the textbox with 2 numericupdown controls.
solution 3
another option is to try to parse it manually.
dim ISvalid as boolean = true
if textbox1.contains(":")
if split(textbox1, ":").count = 2
if split(textbox1, ":").first.length = 2 andalso split(textbox1, ":").last.length = 2
if IsNumeric(split(textbox1, ":").first) andalso isnumeric(split(textbox1, ":").last
' this is a valid value
else
isvalid = false
end if
else
isvalid = false
end if
else
isvalid = false
end if
else
isvalid = false
end if
if isvalid then
Dim MyTime As DateTime = DateTime.ParseExact(txtMyTime.Text, "HH:mm", Nothing)
Dim isoMyTime As String = MyTime.ToString("HH:mm:ss")
end if