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Database Class ADODB Command Recordset VB6 ADO FILE HANDLING OPEN

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18 Nov 2007CPOL5 min read 173.9K   3K   24   2
It is an object of database where we connect the data SQL Server and do working in sqlserver.

Introduction

This is basically a database class. In this project, we connect to SQL Server 2000. We insert, update, delete and select queries. And also fill the grid without using any data control. In this project, I also use file handling.

Using the Code

First, create the private member of the class. The three members of the class are given below:

VB.NET
Private conConnection As New ADODB.connection
Private cmdCommand As New ADODB.Command
Public rstRecordSet As New ADODB.Recordset
  1. ADODB.connection

    First, initialize the adodb connection. This object is used to connect the database.

  2. ADODB.Command

    Second, initialize the command. This object is used to execute the database query.

  3. ADODB.Recordset

    Third, initialize the Recordset. This object is for multiple purposes. I will explain later.

VB.NET
Public Sub connection()
On Error GoTo err1:
    Dim txtserver As String
    Dim txtuser As String
    Dim txtpassword As String
        Dim Filename As String
        Filename = "c:\Label.txt"
        Open (Filename) For Input As #1
        Line Input #1, txtserver
        Line Input #1, txtuser
        Line Input #1, txtpassword
 Close #1
        conConnection.ConnectionString = "Driver={SQL Server};
        Server=" & txtserver & ";Database=Stock_Management;Uid=" & txtuser & ";Pwd=;"
        Exit Sub
err1:
Close #1

       Exit Sub
 
End Sub 

This function establishes the connection with SQL Server 2000. This is a trusted connection, but it is also used for non-trusted connection. It is a user friendly connection. Therefore, here, I use file handling, it just opens the file and reads server name, user name, and password.

For this purpose, I declare the three variables, txtserver, txtuser, txtpassword. First, open object, open the file for reading not writing. Line Input #1 that reads the line number one of the file and the text into the txtserver. And same takes action on the next two lines. and saves value on next two variables, txtuser and txtpassword and close object closes the file. And then, connect to the SQL Server and exit the function.

VB.NET
Public Function conopen() As Boolean
On Error GoTo err1:
        If conConnection.State = 0 Then
        connection
                
                conConnection.Open
                conopen = True
        End If
 
err1:
If Error <> "" Then
MsgBox "Connect to fail"
conclose

       Exit Function
       End If
        
End Function

This function first check the state of the connection if connection is open the leave the without any action. Other wise if connection is close then open the connection and return true.
Note: For checking the connection state, I use connection.State function. If state is one that mean connection is open if state is zero its mean connection is close.

VB.NET
Public Sub insert_query(query As String)
         
        conopen
         
                With cmdCommand
                    .ActiveConnection = conConnection.ConnectionString
                    .CommandText = query
                    .CommandType = adCmdText
                    .Execute (query)
                End With
                
End Sub

This function take a query. Conopen is a function that I am already explain the working of this function. Next it action with the command object. First cmdCommand variable active the connection then it take the query. adCmdText pass to the cmdCommand.CommandType. adCmdText Evaluate as a textual definition. And cmdCommand.execute any query like insert, select, delete and update.

VB.NET
Public Function rstRecordSetOpen()
        
    Call rstRecordSetclose
    
    If rstRecordSet.State = 0 Then
                
               With rstRecordSet
                        .CursorType = adOpenStatic
                        .CursorLocation = adUseClient
                        .LockType = adLockOptimistic
                        .Open cmdCommand
               End With
     End If

End Function

This function open RecordSet object where we populate the data. First, it call the rstRecordSetclose function that closes the RecordSet Object. It is not necessary to close the RecordSet. But sometimes, it creates problems so therefore every time we populate the data, we must close the RecordSet. If you want to more learn about the Recordset, please visit the site.

VB.NET
 Function fillcombo(ByRef combo As ComboBox, query As String, field As Integer)
    
     Call conopen
        
            With cmdCommand
                .ActiveConnection = conConnection.ConnectionString
                .CommandText = query
                .CommandType = adCmdText
            End With
            
        Call rstRecordSetOpen
           
    If rstRecordSet.EOF = False Then
        
            rstRecordSet.MoveFirst
            combo.Clear
                    Do
                            combo.AddItem (rstRecordSet.Fields(field))
                            rstRecordSet.MoveNext
                    Loop Until rstRecordSet.EOF = True
    End If
 
End Function

This function fills the combobox. This function takes three parameters.

  1. Take a combo box name
  2. Take a query
  3. Take a specified, e.g., you write a query like this "Select user_id, User_name from user_table". and you want that all the names show in the combo box, then you pass parameter 1, and after completion, it exits the function.
VB.NET
Function getID(query As String, field As Integer) As Integer
    
     Call conopen
        
            With cmdCommand
                .ActiveConnection = conConnection.ConnectionString
                .CommandText = query
                .CommandType = adCmdText
            End With
            
        Call rstRecordSetOpen
        
    If rstRecordSet.EOF = False Then
            rstRecordSet.MoveFirst
            Dim a As Integer
            a = field
                    Do
                            a = rstRecordSet.Fields(field)
                            rstRecordSet.MoveNext
                            
                    Loop Until rstRecordSet.EOF = True
    End If
    
    getID = a

End Function

And if you want to get Id of any query, then you call this:

VB.NET
Public Function rstRecordSetclose()

    Set rstRecordSet = Nothing

End Function  

For closing the recordset, we use call this function:

VB.NET
Public Function conclose()

        Set conConnection = Nothing
        Set cmdCommand = Nothing
        
End Function

This function closes the command as well as connection.

Here are some screen shots to using this object.

Screenshot - Logon.jpg

Here, we create an object and build a connection. I show the code here how the object is working.

VB.NET
Private Sub cmdOK_Click()
    
        Dim a As String
        Dim database As New clsDatabase
        
        check
        
    If LoginSucceeded = False Then
          
          Exit Sub
          
        Else
              If database.conopen = True Then
              a = "SELECT * from tbl_user where (
                  user_name = '" & txtUserName.Text & "') and (
                  user_password = '" & txtPassword.Text & "')"
     
      
            If database.getID(a, 0) <> 0 Then
                     LoginSucceeded = True
                   MsgBox "logon sucess full"
                   End
                   
                Else
                     MsgBox "Invalid Password, try again!", , "Login"
                     txtPassword.SetFocus
                     SendKeys "{Home}+{End}"
            End If
            Else
            Unload Me
            Set database = Nothing
            frmDatabase.Show
            
            Exit Sub
            End If
            
    End If
       
End Sub 

This is a cmdOK button action. When we click it, it creates a new object in the name of DataBase. First, we call a conOpen function. If connection is open, then we execute the query for getting of a particular row. For this purpose, we call the getID function. The working of this function is that first, it executes the query and then returns the ID of particular row. And prompts the message log on successfully. Here is the screen shot of it.

Screenshot - Logon_success.jpg

If conConnection returns false, there are two, the user name or password is invalid or the connection is not build. And prompt a message connect to fail. Like here.

Screenshot - Logon_fail.jpg

If database object fails to connect the SQL Server 2000. Then prompt the message connect to fail. When you click OK, then a window appears on the screen. Where you see the three text boxes, in the first, that has a label server name detect automatically the server name of your SQL Server 2000, like here.

Screenshot - Connect_data_base.jpg

Then you put the user name and password if have, otherwise you leave blank and click Test button.

VB.NET
Private Sub btntest_Click()
checkfile
data
If database.conopen = True Then
MsgBox "Connect to successfuly"
Unload Me
frmLogin.Show
Else
MsgBox "Connection fail"
End If
End Sub 

When you click Test button. Then first, it goes to the function checkfile.

VB.NET
Function checkfile()
Dim fName As String
fName = "c:\Label.txt"
Dim oFSO As New FileSystemObject
    
  On Error GoTo ErrorHandler
 oFSO.DeleteFile (fName)
   

ErrorHandler:
On Error Resume Next
Set oFSO = Nothing

End Function

On checkfile function, first it declares a variable in the name of fName. fName takes a path of the file. Then we declare a object FileSystemObject in the name of oSFO. It only does one work that deletes the file. Then, it goes back in the btnTest click event. And then, btntest click event calls another function Data. We look at the following working of data function.

VB.NET
Function data()
On Error GoTo err1

 Open "c:\Label.txt" For Append As #1
    Print #1, Me.txtservername
    Print #1, Me.txtusername
    Print #1, Me.txtpassword
      Close #1

If Error <> "" Then
err1:
Close #1
data
Exit Function
End If
End Function 

Note: detail of Open

Main function of OPEN is to associate a file number (filenum&) with a file or physical device and to prepare that device for reading and/or writing. This file number is then used, rather than its name, in every statement that refers to the file. The FREEFILE function can be used to determine the next available file number, or you can pick one yourself. The OPEN statement contains information on the mode of the file; that is, the methods by which the file will be accessed: sequential (for input/output to a new file, or output to an existing file), random access, and binary. An OPEN statement is usually balanced by a matching CLOSE statement.

Open function opens the file if file does not exist, then create a new file. Above, we have declared three variables that take server name, user name and password. The print function writes these values into the file and Close function closes the file.

That is a little bit of an overview of the object of clsDataBase.

Important Note: If you run this code, first attach the database into your SQL Server that I have provided you.

If you have any problems with this topic, please leave a message in the Comments section below.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


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Comments and Discussions

 
GeneralMy vote of 1 Pin
Lounge Lizard16-Apr-09 9:50
Lounge Lizard16-Apr-09 9:50 
GeneralRe: My vote of 1 Pin
M Saqib Ali22-Dec-09 1:28
M Saqib Ali22-Dec-09 1:28 

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