How can I use multiple connection in If else code blocks? - vb.net

Question

I want to use multiple connection in if else code block but it's giving the following error when I checked in a Messagebox :
"Argument prompt cannot be converted to string"
Here is my code :
Try
Conn.Open()
Com.CommandText = "Select * FROM Table1 WHERE ID=" & txtID.Text & " AND DOR=#01/01/1900# AND Paid = '0' ORDER BY DOI"
Dr = Com.ExecuteReader
If Dr.Read = True Then
txtInstNo.Text = Dr(2)
txtInstAmount.Text = Dr(4)
Else
If MsgBox("Wait! You're not allowed to do it. Do you still want to continue ? ", MsgBoxStyle.YesNo Or MsgBoxStyle.Question, "Alert") = MsgBoxResult.Yes Then
Try
Dim Con As New OleDbConnection
Dim Comm As New OleDbCommand
Dim Dr2 As OleDbDataReader
Con.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database.accdb"
Con.Open()
Comm.Connection = Con
Comm.CommandText = "Select * FROM Table1 WHERE ID=" & txtID.Text & " AND DOR=#01/01/1900# AND Paid = '0' ORDER BY DOI"
Comm.CommandType = CommandType.Text
Dr2 = Comm.ExecuteReader
MsgBox(Dr2) <-- Here I got that error
If Dr.Read = True Then
txtInstNo.Text = Dr(2)
txtInstAmount.Text = Dr(4)
Else
MsgBox("Sorry, no record found",MsgBoxStyle.Exclamation, "Alert")
End If
Dr2.Close()
Con.Close()
Catch ex As Exception
MsgBox(ex.Message)
End Try
End If
End If
Dr.Close()
Conn.Close()
Catch ex As Exception
MsgBox(ex.Message)
End Try

Answer 1

Your query might be returning entire rows, objects, widgets or whatever. As #Andrew Morton pointed out, it's a Data Reader. It's not going to implicitly convert your result. You'll have to manipulate your reader result and convert it to a string to do anything useful. You'll also have to handle if your DataReader returns a null result, which when converted should be "" an empty string.
If you just want to see what Dr2 contains, you could try MsgBox(CStr(Dr2)). No error handling, if it throws an exception.

Answer 2

There are a few things which could be modified in your code to make it a bit shorter and so easier to track down what is not working. It is easier to isolate a problem if you have the minimal amount of code which shows the problem: How to create a Minimal, Complete, and Verifiable example.
I'll show my suggestion for a minimal amount of code on a new form which should help you narrow down where the problem is, and then I'll go over why I have written it that way and what could be going wrong.
Option Strict On
Option Infer On
Imports System.Data.OleDb
Public Class Form1
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim connStr = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=|DataDirectory|\Database.accdb"
Dim sql = "SELECT InstNo, InstAmount FROM Table1 WHERE ID = ? AND DOR = #01/01/1900# AND PAID='0' ORDER BY DOI"
' lists to hold the retrieved data
Dim instNos As New List(Of String)
Dim instAmounts As New List(Of String)
' get the data
Using conn As New OleDbConnection(connStr)
Using cmd As New OleDbCommand(sql, conn)
cmd.Parameters.Add(New OleDbParameter With {.ParameterName = "#ID",
.DbType = DbType.String,
.Value = txtID.Text})
conn.Open()
Dim rdr = cmd.ExecuteReader()
While rdr.Read
instNos.Add(rdr.GetString(0))
instAmounts.Add(rdr.GetString(1))
End While
End Using
End Using
' act on the data
If instNos.Count = 0 Then
MsgBox(String.Format("No records were found for ID ""{0}"".", txtID.Text))
Else
txtInstNo.Text = String.Join(vbCrLf, instNos)
txtInstAmount.Text = String.Join(vbCrLf, instAmounts)
End If
End Sub
End Class
The code.
I start with Option Strict On to make sure that all data types match up and I haven't done anything else silly which Visual Studio can point out to me.
I use Option Infer On so that I don't have to type out the type of variables when the compiler can infer what they are.
I used just one Button on the form along with the three named textboxes as we are going for minimal code.
I set up the two strings which are going to be used in one place at the top of the sub because it is easier to maintain the code that way. Normally, you would declare variables just before they are used to minimise their scope.
I specified exactly which columns I want from the database. There is no point retrieving all of them with *. I had to guess what the columns are called - you will need to put in the actual names if they are different.
The result of a query to the database might have more than one record, so I initialise Lists for the data. (Your query has an ORDER BY so I assume that there could be more than one record.)
The Using statement makes sure that resources are released cleanly whatever else happens.
For OleDb, parameters are normally represented by a ?. (If there is more than one, they are all represented by question marks and the parameters must be added in the order in which they are to be put into the query.) I had to guess at the data type for the ID column - please put in the correct type. When you create the parameter, you can still use a meaningful name for it, even though it is ignored by the computer.
Next, the data (if any) is read. I do nothing else at this point except read the data to keep it fast and tidy. I assumed that the data to be retrieved is strings, hence the GetStrings. You should adjust that if required, and also the types of the Lists to match.
Now that the data has been read, I act on it. If there was no data, show an appropriate message, and if there was data then I put it into multiline textboxes to show it. Note that I wrote multiline: if it was a single line textbox then only the last line would be visible. Other ways of displaying it could be more useful, for example a DataGridView - in which case I might have read the data into a DataTable or a list of some class.
What could go wrong.
In your query, you have AND DOR = #01/01/1900# - is this correct?
In your query, you have AND PAID = '0' - is PAID actually a string? If it is a number then it should be AND PAID = 0. (The DB should convert the string "0" to the number zero, but why make it do extra work?)
Now that you have multiline textboxes for the results, you can see if it just happens that the last records found happened to be blank, and are simply not visible in a single-line textbox.
Finally, are you sure it is using the correct database file?