Getting Data From SQL and into a variable - sql

Question

NET and using MS Access as database. I'm trying to get data from SQL and place it in a variable and print it in a Message box to confirm that the variable holds the data. But when I run my code it gives me an error message and highlights
Dim conn As New OleDbConnection and conn.Open()
"An unhandled exception of type 'System.InvalidOperationException' occurred in System.Data.dll
Additional information: The ConnectionString property has not been initialized."
It does not run the sql query. Please help me figure this out. Merci.
Imports System.Data.OleDb
Public Class ModifyForm
Dim connstring As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source= c:\Databse\Company_db.accdb"
Dim conn As New OleDbConnection
Private Sub eNumText_SelectedIndexChanged(sender As Object, e As EventArgs) Handles eNumText.SelectedIndexChanged
Dim empNum As String
Dim empFname As String
Dim empLname As String
Dim empDept As String
Dim empStat As String
Dim empYears As String
empNum = eNumText.Text
empFname = empFnameText.Text
empLname = empLnameText.Text
empDept = DeptText.Text
empStat = StatText.Text
empYears = yearstext.Text
Dim conn As New OleDbConnection(connstring)
conn.Open()
Dim DBID As String ' Or whatever type you're using for the ID field
Dim DBFirstName As String
Dim SqlQuerry As String = "SELECT * FROM tbl_empinfo WHERE EmpID like empNum"
Dim SqlCommand As New OleDbCommand
Dim SqlAdapter As New OleDbDataAdapter
Dim Table As New DataTable
With SqlCommand
.CommandText = SqlQuerry
.Connection = conn
End With
With SqlAdapter
.SelectCommand = SqlCommand
.Fill(Table)
End With
For i = 0 To Table.Rows.Count - 1
DBID = Table.Rows(i)("EmpID")
DBFirstName = Table.Rows(i)("FirstName")
MsgBox(DBID)
MsgBox(DBFirstName)
Next
conn.Close()
End Sub
End Class

Answer 1

You need to actually use your connection string.
But first let's remove the duplicate declaration of your connection. Remove Dim conn As New OleDbConnection from the very top of your code (the one outside of the method) it's not needed since you are declaring again inside of the method. Then, inside the method update your connection initialization to:
Dim conn As New OleDbConnection(connstring)
More than that, you need to initialize your command, passing it the connection string and query string. The Adapter needs to have a reference to the command and you need to call
SQLAdapter.fill(Table)
To get your data in the table.
Please look up how to use these objects... Simply creating new instances of them doesn't implicitly assign all of the configuration information that each object needs.
One note is to make sure that you dispose your objects that implement the IDisposable interface to free the unmanaged resources. It is not enough to simply close your connection--this will lead to memory leaks, not just with SQL objects but anything that uses resources not directly managed by. .NET
SQLCommand.dispose()
SQLAdapter.dispose()
Table.dispose()
conn.dispose()
conn.close()
And finally, once you get it working using the information provided above and some googling, you then need to address SQLInjection. Right now your query string is prone to injection whereas a user could potentially type some malicious text into the text box you refer to in your query string and manipulate your database without your permission. To get around this, look into parameterized commands.
I'm posting from my phone or else I'd provide a full working set of code; but at the same time I don't want to rewrite the whole thing for you. There should be enough info in this answer to help you do a little research.
This MSDN page contains info on the OleDb data adapter as well as a short example at the end. It also includes links and references for the rest of the OleDb classes and to some tutorials:
http://msdn.microsoft.com/en-us/library/system.data.oledb.oledbdataadapter.aspx
This MSDN page contains info on the SQLDataAdapter and includes a short example at the very bottom. Although a different class, the usage is fundamentally the same as the OleDb classes: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldataadapter.aspx
Though not in vb (its in c#) the usage is the same, just slightly different syntax (best I could find from my phone at the moment). Again this is for the SQLDataAdapter class, but usage is fundamentally the same: http://www.codeproject.com/Tips/462730/Five-different-overloads-of-the-DataAdapter-Fill-m