Vb.net with access database: How can you help me simplify these codes? - vb.net

Question

this is my code:
'Set up connection string
Dim cnString As String
cnString = "Provider=Microsoft.Jet.OLEDB.4.0;Persist Security Info=False;Data Source=..\data\testingDB.mdb"
Dim sqlQRY As String = "SELECT * " & _
"FROM users " & _
"WHERE firstName = '" & TextBox1.Text & "' " & _
" AND lastName = '" & TextBox2.Text & "'"
'Create connection
Dim conn As OleDbConnection = New OleDbConnection(cnString)
Try
' Open connection
conn.Open()
'create data adapter
Dim da As OleDbDataAdapter = New OleDbDataAdapter(sqlQRY, conn)
'create dataset
Dim ds As DataSet = New DataSet
'fill dataset
da.Fill(ds, "user")
'get data table
Dim dt As DataTable = ds.Tables("user")
'display data
Dim row As DataRow
If TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) And dt.Rows(0).Item(5) = 10 Then
MsgBox("10")
ElseIf TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) And dt.Rows(0).Item(5) = 9 Then
MsgBox("9")
ElseIf TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) Then
MsgBox("SUCCESS")
Else
MsgBox("fail")
End If
Catch ex As OleDbException
MsgBox("Error: " & ex.ToString & vbCrLf)
Finally
' Close connection
conn.Close()
End Try
I'm trying it to make it simple with the same results. As you can see the if-else statements were messy but it works 100%. I do want the if-else statements to be simple and works the same as above.

Answer 1

Edited to check value of row(5) for DbNull values
try this for if-else statements:
Dim row As DataRow = dt.Rows(0)
Dim r5 as Object = row(5)
If IsDbNull(r5) then r5 = 0
If TextBox1.Text = row(1) And TextBox2.Text = row(2) Then
Select Case r5
Case 10, 9 : MsgBox(r5)
Case Else : MsgBox("SUCCESS")
End Select
Else
MsgBox("fail")
End If

Answer 2

Dim cmd as New OledbCommand
Dim sqlQRY As String = "SELECT count(*) " & _
"FROM users " & _
"WHERE firstName = #fname " & _
" AND lastName = #lname"
cmd.parameters.add("#fname",TextBox1.Text)
cmd.parameters.add("#lname",TextBox2.Text)
Dim Cnt as Integer
cmd = new oledbcommand(sqlQRy,con)
Cnt = Convert.ToInt32( cmd.ExecuteScalar())
if Cnt>=1 then
msgbox("Success")
else if
msgbox("Failure")
end if

Answer 3

You must be aware that your SQL could logically return more than 1 row. You need to make sure that when you read data that you intend to test in this way, that your SQL uses a primary key and return 1 row only otherwise, problems could happen when more data is added. I suggest you first ensure that exactly 1 row is returned before you perform your if test (see my comment to #SenthilKumar). You need to send appropriate message to user when no rows are found and not perform the test.
If you get exactly 1 row back, you have to ensure that the data is not null (if applicable, this depends on how your columns are defined).
Remember that data that comes form UI could be padded with blanks or be in mixed case. You may need to watch for this.
Your IF statement is not too complex as is.I am not sure what you are testing exactly, but one can observe that you are using the following conditions:
TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) And dt.Rows(0).Item(5)
TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) And dt.Rows(0).Item(5)
TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2)
You can see that the the expression
dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2) is common. You can assign the value to a Boolean expression and use it in your test.
You also should not include non-database processing in the scope of your try.

Answer 4

Just more little simpler ..
If TextBox1.Text = dt.Rows(0).Item(1) And TextBox2.Text = dt.Rows(0).Item(2)
MsgBox("SUCCESS - " & format(dt.Rows(0).Item(5)))
Else
MsgBox("fail")
End If