using LINQ-to-SQL in vb.net with multiple select statement - linq-to-sql

Question

I'm very new to vb.net and LINQ to SQL.
I have been trying the whole day to do this but it doesn't seem to work at all. all your help is highly appreciated.
I have a table named users which contains 4 columns
+---------+-----------+---------------+--------------+
| user_id | user_name | user_password | user_stopped |
+---------+-----------+---------------+--------------+
| 1 | admin | admin | false |
| 2 | user2 | 2 | false |
| 3 | user3 | 3 | true |
+---------+-----------+---------------+--------------+
I have a from with three textboxes "txtuserid" & "textusername" & "txtuserpassword" and a button name "login"
1) on the "on_click" event of the "login" button , I have this query
Dim query = From check In Me.MydatabaseDataSet.users
Where check.user_id = Me.txtuserid.Text
Select check.user_name, check.user_password, check.user_stopped
I want to do something like this:
if query.check.user_stopped= true then
msgbox("this user has no permission")
else
me.txtusername.text= query.user_name
if me.txtuserID.text= query.check.user_id and
me.txtuserpassword.text= query.check.user_password then
me.hide()
form2.show()
end if
end if
I have been trying for hours but nothing seems to work at all.
I'm using VB.net 2010 with SQL database.
All your help is highly appreciated.

Answer 1

In fact Linq is really simple.
Dim id as Integer
integer.TryParse(Me.txtuserid.Text, id)
Dim query = From check In Me.MydatabaseDataSet.users
Where check.user_id = id
Select check
Would simply return all users with a given Id (Me.txtuserid.Text - converted to integer, it is an integer, right?).
If you specifically want 3 columns:
Dim query = From check In Me.MydatabaseDataSet.users
Where check.user_id = id
Select New With {check.user_name, check.user_password, check.user_stopped}
But keep in mind, this version is returning anonymous type where previous one returns User type.
If you think about it, user_id is a primary key (unique). Thus you don't need to get back a "collection" as the above "query", you simply need a single User:
Dim user = Me.MydatabaseDataSet.users.SingleOrDefault(Function(check) check.user_id = id)
If that ID exists than the user has properties of that user (typed data), else NULL.
This one matches to code that you later want to execute:
if user is not nothing
msgbox("unknown user")
else
if user.user_stopped= true then
msgbox("this user has no permission")
else
me.txtusername.text= user.user_name
if me.txtuserID.text= user.user_id and
me.txtuserpassword.text= user.user_password then
me.hide()
form2.show()
end if
end if
end if
Note: I assume this is just for hobby testing purposes, in real world you would never want to store plain text passwords.