How to check empty fields using VB.NET

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Hello to everybody! Can you guys help me? I'm using VB.NET and an MS Access database to build an ordering system. In order to remind the user to fill out all fields, I wanted to include a message box, but I'm not sure where to put it. This is my code; all text boxes must have the required information in before they may submit. Please be gentle with me; I'm a beginner. Thankyou.

What I have tried:

ds = New DataSet
adapter = New OleDbDataAdapter("insert into [tblaccts] ([USERNAME],[PASSWORD],[STORE NAME], [IMAGE PATH]) VALUES " &
"('" & usr1.Text & "','" & password1.Text & "','" & storeName.Text & "','" & imagepath.Text & "')", conn)

adapter.Fill(ds, "tblaccts")
usr1.Clear()
password1.Clear()
storeName.Clear()
imagepath.Clear()
PictureBox1.Image = Nothing

GetRecords()

Posted 31-Oct-22 4:59am

Hazel Ann Torno

Updated 31-Oct-22 20:34pm

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Richard Deeming 31-Oct-22 11:21am

So many problems in such a small sample of code!

Let's start with the most serious: Your code is vulnerable to SQL Injection[^]. NEVER use string concatenation/interpolation to build a SQL query. ALWAYS use a parameterized query.

Richard Deeming 31-Oct-22 11:22am

Then there's the fact that you're storing your users' passwords insecurely.
Secure Password Authentication Explained Simply[^]

Richard Deeming 31-Oct-22 11:23am

Then we move on to the fact that you're using a DataAdapter to fill a DataSet, but the query you're executing is an INSERT, which doesn't return any records. You should use an OleDbCommand and call ExecuteNonQuery instead.

Hazel Ann Torno 31-Oct-22 11:35am

Actually sir, a record from the database is displayed after users click the add button. I simply wanted to add a message box so that I could let them know that all text boxes must be filled out and should not be left empty.

Richard Deeming 31-Oct-22 11:43am

No. If the columns are required, you need to validate that the user has entered something in all of the textboxes before you try to insert the record in the database.

Hazel Ann Torno 31-Oct-22 11:46am

That is indeed my problem. And I have no idea how to code that. Please be patient; I'm only a student attempting to develop a system for my project.

Richard Deeming 31-Oct-22 11:24am

The spaces in your column names are not a good idea. As you've already found out, since you have to enclose them in square brackets every time you reference them. Far better to stick to names with only alphanumeric characters and (optionally) underscores.

Richard Deeming 31-Oct-22 11:26am

And there's nothing in the code you've shown to validate that the user has entered valid values in any of the textboxes. And that's before you get into issues that arise if they enter a username that already exists - do you have a unique index/constraint within the database to prevent that?

Member 15627495 31-Oct-22 13:25pm

for each _field in form1.controls
if typeof _field is textbox and _field.Text = vbnullstring then
msgbox("empty field")
end if
next

this way you fetch all controls on your form, then you check the type of the control,
if it's a textbox, and if the field is 'empty', a messagebox will pop.

vbnullstring is equal to "" , by a inner VB constant.

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RickZeeland · Accepted Answer · 2022-10-31T20:34:00

In addition to Richards tips, take a look at:
Validating User Input with VB.NET | CodeGuru[^]

It shows how to validate TextBox fields before submitting them, you should also check if the input text lengths fit in the database fields, which is quite simple to implement.

If you want to give the user a visual clue in the form, you can drag an error provider from the toolbox in the form that will show as a red bullet, see:
ErrorProvider Class (System.Windows.Forms) | Microsoft Learn[^]

And maybe this will make things more clear: Visual Studio 2010 ErrorProvider control in VB.NET[^]