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OleDb Basics in VB.Net

OleDb Basics in VB.Net

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PsychoCoder
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24 Sep, 2007 - 06:53 AM

Post #1

In todays tutorial we will be discussing the basics of interacting with Access (or any other than require the OleDb Objects) in VB.Net. These code ideas will be from a Windows Application, but with some (if any) modifications they can be used in a VB.Net Web Application. All the function in this tutorial are Public Shared because I always put them in their own class file, this way I can reference the class file itself, and not have to create a new instance of it.

If your project don't already have one add an app.config file, in it you will be storing your connection string information for later retrieval. Your connection should look like this:

CODE

< connectionStrings>
    <add name="YourConnectionName"
   connectionString="Persist Security Info=False;
   Data Source=YourDatabase;
   Initial Catalog=YourTable;
   Integrated Security=SSPI;
   Trusted_Connection=TRUE;
   Application Name=SampleVBNetApplication"
   providerName="System.Data.OleDb" />
  </connectionStrings>

We will be referencing this connectionString in our next code snippet. Add a new Class and name it DataAccess, then at the top of you class add this Imports statement

CODE

Imports System.Data.OleDb

This is needed for working with OleDb Objects in the .Net Framework. The first code you will add to this class is a method to retrieve the connectionString from the app.config file. The method is GetConnectionString, and it includes this code:

CODE

''' <summary>
''' Function to retrieve the connection from the app.config
''' </summary>
''' <param name="conName">Name of the connectionString to retrieve</param>
''' <returns></returns>
''' <remarks></remarks>
Public Shared Function GetConnectionString(ByVal conName As String) As String
     'variable to hold our connection string for returning it
     Dim strReturn As New String("")
     'check to see if the user provided a connection string name
     'this is for if your application has more than one connection string
     If Not String.IsNullOrEmpty(conName) Then
         'a connection string name was provided
         'get the connection string by the name provided
          strReturn = ConfigurationManager.ConnectionStrings(conName).ConnectionString
     Else
         'no connection string name was provided
         'get the default connection string
         strReturn = ConfigurationManager.ConnectionStrings("YourConnectionName").ConnectionString
     End If
     'return the connection string to the calling method
     Return strReturn
End Function

Now, this method does several things:

Checks to see if a connection name was provided
If one was provided get the connection information for that name
If one wasnt provided it returns the default connection information (as set by you the developer)
Return the connection information to the calling method

Most people are retrieving data for populating a control, whether it be a DataGrid, A DataRepeater, etc. The easiest way I've found to populate these controls is with a BindingSource. According to the MSDN, this is the definition of a Binding Source:

QUOTE

The BindingSource component serves many purposes. First, it simplifies binding controls on a form to data by providing currency management, change notification, and other services between Windows Forms controls and data sources. This is accomplished by attaching the BindingSource component to your data source using the DataSource property.

More: BindingSource

So to retrieve a BindingSource for a Data control I use a function that I pass a OleDbCommand Object to it, it then executes that OleDbCommand Object and puts the returned data into a BindingSource Object for me, making it easy to bind to a control. This function looks like this:

CODE

''' <summary>
''' Returns a BindingSource, which is used with, for example, a DataGridView control
''' </summary>
''' <param name="cmd">"pre-Loaded" command, ready to be executed</param>
''' <returns>BindingSource</returns>
''' <remarks>Use this function to ease populating controls that use a BindingSource</remarks>
Public Shared Function GetBindingSource(ByVal cmd As OleDbCommand) As BindingSource
    'declare our binding source
    Dim oBindingSource As New BindingSource()
    ' Create a new data adapter based on the specified query.
    Dim daGet As New OleDbDataAdapter(cmd)
    ' Populate a new data table and bind it to the BindingSource.
    Dim dtGet As New DataTable()
    'set the timeout of the OleDbCommandObject
    cmd.CommandTimeout = 240
    dtGet.Locale = System.Globalization.CultureInfo.InvariantCulture
    Try
        'fill the DataTable with the OleDbDataAdapter
         daGet.Fill(dtGet)
    Catch ex As Exception
        'check for errors
        MsgBox(ex.Message, "Error in GetBindingSource")
        Return Nothing
    End Try
    'set the DataSource for the BindingSource to the DataTable
    oBindingSource.DataSource = dtGet
    'return the BindingSource to the calling method or control
    Return oBindingSource
End Function

Heres how the GetBindingSource method works:

Pass the method your OleDbCommand Object from your method (this is already created and "pre-loaded" when you pass it)
Create a OleDbDataAdapter Object based on this OleDbCommand Object
Create and fill a DataTable Object with the OleDbDataAdapter (this executes your OleDbCommand Object)
Set the DataSource property of your BindingSource Object to you now filled DataTable Object
Return the BindingSource Object to the calling method for binding

The last thing to add to your DataAccess class is a way to open and close the OleDbConnection based on its current state. I created a method called HandleConnection, and you pass a OleDbConnection then the method checks the status of the connection and acts accordingly. This procedure looks like this:

CODE

''' <summary>
''' Method for handling the ConnectionState of
''' the connection object passed to it
''' </summary>
''' <param name="conn">The OleDbConnection Object</param>
''' <remarks></remarks>
Public Shared Sub HandleConnection(ByVal conn As OleDbConnection)
    With conn
        'do a switch on the state of the connection
        Select Case .State
            Case ConnectionState.Open
               'the connection is open
               'close then re-open
               .Close()
               .Open()
               Exit Select
          Case ConnectionState.Closed
               'connection is open
               'open the connection
              .Open()
              Exit Select
         Case Else
             .Close()
             .Open()
             Exit Select
         End Select
    End With
End Sub

This covers 3 important methods, and also saves a lot of coding down the road. For the next part you can either keep them in the DataAccess Class (my choice) or put it right in your form .vb file.

First I will show you how to insert a new record into a table. For this I create a Public Shared Function that returns a boolean value (True for succeeded, False for failed). Always use a Try...Catch block to help catch and deal with any errors that may occur, especially when working with a database.

In this function we pass the values we want inserted into our table (I only have 3 in this example, there can be as many as you need though). We then create the objects we need for this, OleDbCommand, OleDbConnection and a String variable query. We set the query variable to the query we want to execute (or the inline SQL if you go that route), then we set the properties of our OleDbCommand Object.

Once this is complete we open the connection to the database, we use ExecuteNonQuery to insert the values. ExecuteNonQuery is what you use when you're not returning a value from the database. Once we complete the insert we check the status and act accordingly, then we close the connection. Here is more on the objects we created

A OleDbCommand Object -> This will perform your query execution
A OleDbConnection -> This will be used to communicate with the database
A String (query) -> This will hold the name of your query

Now to the function:

CODE

Public Shared Function InsertNewRecord(ByVal item1 As String, ByVal item2 As String, ByVal item3 As String) As Boolean
    'Create the objects we need to insert a new record
    Dim cnInsert As New OleDbConnection(GetConnectionString("YourConnName"))
    Dim cmdInsert As New OleDbCommand
    Dim query As String = "INSERT INTO YourTable(column1,column2,column3) VALUES(@item1,@item2,@item3)"
    Dim iSqlStatus As Integer

    'Clear any parameters
    cmdInsert.Parameters.Clear()
    Try
       'Set the OleDbCommand Object Properties
       With cmdInsert
          'Tell it what to execute
          .CommandText = query
          'Tell it its a text query
          .CommandType = CommandType.Text
          'Now add the parameters to our query
          'NOTE: Replace @value1.... with your parameter names in your query
          'and add all your parameters in this fashion
          .Parameters.AddWithValue("@value1", item1)
          .Parameters.AddWithValue("@value2", item2)
          .Parameters.AddWithValue("@value3", item3)
          'Set the connection of the object
          .Connection = cnInsert
      End With

      'Now take care of the connection
      HandleConnection(cnInsert)

      'Set the iSqlStatus to the ExecuteNonQuery
      'status of the insert (0 = failed, 1 = success)
      iSqlStatus = cmdInsert.ExecuteNonQuery

      'Now check the status
      If Not iSqlStatus = 0 Then
          'DO your failed messaging here
          Return False
      Else
         'Do your success work here
          Return True
      End If
    Catch ex As Exception
       MsgBox(ex.Message, "Error")
    Finally
        'Now close the connection
        HandleConnection(cnInsert)
    End Try
End Function

Next we will look at updating a record in the database. In this function we pass the values of the record we want to update, along with the id of the record to update (I only have 2 values in this example but you can have more in yours). We then create the objects we need for this, OleDbCommand, OleDbConnection and a String variable query. We set the query variable to the query we want to execute, then we set the properties of our OleDbCommand Object.

Once this is complete we open the connection to the database, we use ExecuteNonQuery to insert the values. ExecuteNonQuery is what you use when you're not returning a value from the database. Once we complete the insert we check the status and act accordingly, then we close the connection. Here is the function:

CODE

Public Shared Function UpdateRecord(ByVal item1 As String, ByVal item2 As String, ByVal id As Integer) As Boolean
    'Create the objects we need to insert a new record
    Dim cnUpdate As New OleDbConnection(GetConnectionString("YourConnName"))
    Dim cmdUpdate As New OleDbCommand
    Dim query As String = "UPDATE YourTable SET column1 = @item1,column2 = @item2 WHERE YourId = @id"
    Dim iSqlStatus As Integer

    'Clear any parameters
    cmdUpdate.Parameters.Clear()
    Try
        'Set the OleDbCommand Object Properties
        With cmdUpdate
            'Tell it what to execute
            .CommandText = query
            'Tell it its a text query
            .CommandType = CommandType.Text
            'Now add the parameters to our query
            'NOTE: Replace @value1.... with your parameter names in your query
            'and add all your parameters in this fashion
            .Parameters.AddWithValue("@value1", item1)
            .Parameters.AddWithValue("@value2", item2)
            .Parameters.AddWithValue("@YourID", id)
            'Set the connection of the object
            .Connection = cnUpdate
        End With

        'Now take care of the connection
        HandleConnection(cnUpdate)

        'Set the iSqlStatus to the ExecuteNonQuery
        'status of the insert (0 = success, 1 = failed)
        iSqlStatus = cmdUpdate.ExecuteNonQuery

        'Now check the status
        If Not iSqlStatus = 0 Then
            'DO your failed messaging here
            Return False
        Else
            'Do your success work here
            Return True
        End If
    Catch ex As Exception
        MsgBox(ex.Message, "Error")
    Finally
        'Now close the connection
        HandleConnection(cnUpdate)
    End Try
End Function

Next we will look at deleting a record from a table. In this function we pass the id of the record we want to delete. We then create the objects we need for this, OleDbCommand, OleDbConnection and a String variable query. We set the query variable to the query we want to execute, then we set the properties of our OleDbCommand Object.

Once this is complete we open the connection to the database, we use ExecuteNonQuery to insert the values. ExecuteNonQuery is what you use when you're not returning a value from the database. Once we complete the insert we check the status and act accordingly, then we close the connection. Here is the function:

CODE

Public Shared Function DeleteRecord(ByVal id As Integer) As Boolean
    'Create the objects we need to insert a new record
    Dim cnDelete As New OleDbConnection(GetConnectionString("YourConnName"))
    Dim cmdDelete As New OleDbCommand
    Dim query As String = "DELETE FROM YourTable WHERE YourID = @id"
    Dim iSqlStatus As Integer

    'Clear any parameters
    cmdDelete.Parameters.Clear()
    Try
        'Set the OleDbCommand Object Properties
        With cmdDelete
            'Tell it what to execute
            .CommandText = query
            'Tell it its a text query
            .CommandType = CommandType.Text
            'Now add the parameters to our query
            'NOTE: Replace @value1.... with your parameter names in your query
            'and add all your parameters in this fashion
            .Parameters.AddWithValue("@YourID", id)
            'Set the connection of the object
            .Connection = cnDelete
        End With

        'Now take care of the connection
        HandleConnection(cnDelete)

        'Set the iSqlStatus to the ExecuteNonQuery
        'status of the insert (0 = success, 1 = failed)
        iSqlStatus = cmdDelete.ExecuteNonQuery

        'Now check the status
        If Not iSqlStatus = 0 Then
            'DO your failed messaging here
            Return False
        Else
            'Do your success work here
            Return True
        End If
    Catch ex As Exception
        MsgBox(ex.Message, "Error")
        Return False
    Finally
        'Now close the connection
        HandleConnection(cnDelete)
    End Try
End Function

So far we have covered:

Retrieving the connectionString from the app.config
Retrieving a BindingSource for binding our data to a control
A method to open and close our connection
Inserting a new record into the database
Updating a record in the database
Deleting a record from a database

Next we will look at a basic retrieval of data from the database. This method will return a populated BindingSource so you can bind it to your data control and display your data. A SQL no parameters is the simplest database query, but lets say you want to filter your data by only returning certain data that falls into a certain category, you would then need parameters in your query. First lets take a look at returning all the data in the table, this function looks like this:

CODE

Public Shared Function GetRecords() As BindingSource
    'The value that will be passed to the Command Object (this is a query)
    Dim query As String = "SELECT * FROM YourTableName"
    Dim cnGetRecords As New OleDbConnection(GetConnectionString("YourConnectionName"))
    'OleDbConnection Object to use
    Dim cmdGetRecords As New OleDbCommand()
    'OleDbCommand Object to use
    Dim daGetRecords As New OleDbDataAdapter()
    Dim dsGetRecords As New DataSet()
    'Clear any parameters
    cmdGetRecords.Parameters.Clear()
    Try
        With cmdGetRecords
            'set the OleDbCommand Object Parameters
            .CommandText = query
            'tell it what to execute
            .CommandType = CommandType.Text
            'Set the Connection for the Command Object
            .Connection = cnGetRecords
        End With
        'set the state of the OleDbConnection Object
        HandleConnection(cnGetRecords)
        'create BindingSource to return for our DataGrid Control
        Dim oBindingSource As BindingSource = GetBindingSource(cmdGetRecords)
        'now check to make sure a BindingSource was returned
        If Not oBindingSource Is Nothing Then
            'return the binding source to the calling method
            Return oBindingSource
        Else
            'no binding source was returned
            'let the user know the error
            Throw New Exception("There was no BindingSource returned")
            Return Nothing
        End If
    Catch ex As Exception
        MsgBox(ex.Message, "Error Retrieving Data")
        Return Nothing
    Finally
        HandleConnection(cnGetRecords)
    End Try
End Function

Next we will look at retrieval of data based on a criteria, a filter if you will. This method will return a populated BindingSource so you can bind it to your data control and display your data. A query with no parameters is the simplest database query, but lets say you want to filter your data by only returning certain data that falls into a certain category, you would then need parameters in your query. This function looks like this:

CODE

Public Shared Function GetRecordsByID(ByVal value As Integer) As BindingSource
    'The value that will be passed to the Command Object (this is a query)
    Dim query As String = "SELECT value1,value2,value3 FROM YourTable WHERE YourValue = @value"
    Dim cnGetRecords As New OleDbConnection(GetConnectionString("YourConnectionName"))
    'OleDbConnection Object to use
    Dim cmdGetRecords As New OleDbCommand()
    'OleDbCommand Object to use
    Dim daGetRecords As New OleDbDataAdapter()
    Dim dsGetRecords As New DataSet()
    'Clear any parameters
    cmdGetRecords.Parameters.Clear()
    Try
        With cmdGetRecords
            'set the OleDbCommand Object Parameters
            .CommandText = query
            'tell it what to execute
            .CommandType = CommandType.Text
            'tell it its executing a text query
            'heres the difference from the last method
            'here we are adding a parameter to send to our query
            'you use the AddWithValue, then the name of the parameter in your query
            'then the variable that holds that value
            .Parameters.AddWithValue("@id", value)
            'Set the Connection for the Command Object
            .Connection = cnGetRecords
        End With
        'set the state of the OleDbConnection Object
        HandleConnection(cnGetRecords)
        'create BindingSource to return for our DataGrid Control
        Dim oBindingSource As BindingSource = GetBindingSource(cmdGetRecords)
        'now check to make sure a BindingSource was returned
        If Not oBindingSource Is Nothing Then
            'return the binding source to the calling method
            Return oBindingSource
        Else
            'no binding source was returned
            'let the user know the error
            Throw New Exception("There was no BindingSource returned")
            Return Nothing
        End If
    Catch ex As Exception
        MsgBox(ex.Message, "Error Retrieving Data")
        Return Nothing
    Finally
        'Close the connection
        HandleConnection(cnGetRecords)
    End Try
End Function

There is essentially one difference in this method and the previous one, its the line cmdGetRecords.Parameters.AddWithValue("@id", value). The AddWithValue accepts 2 parameters:

The parameter name in your query (for this example the name is @year)
The variable that is holding that value (in this case we pass it with the signature of the method -> value)

Now to use these methods in your form for binding a DataGridView to the data use this

CODE

'for binding to returning all the records
DataGridView1.DataSource = DirectCast(GetAllRecords(), BindingSource)

'for binding to to returning certain records
DataGridView1.DataSource = DirectCast(GetRecordsByID(DirectCast(TextBox1.Text, Integer)), BindingSource)

Her are the objects we used during this tutorial

If you have any questions please post them here so I can asnwer the question for you and anyone else who might have the same questions. Thanks for reading

Happy Coding!

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ThomasF

12 May, 2008 - 03:13 AM

Post #2

Hi PsychoCoder!
First of all many thanks for your tutorial!
How would a function look like where we only expect one value back and want to feed that into a variable.
A "select count(*)" statement, e.g.?
Many thanks in advance!

shavian

10 Jan, 2009 - 10:00 AM

Post #3

I am using 2005 Express Edition and have successfully added an SQL database to my application.

The app.config looks OK and Imports System.Data.OleDb is present.

I am now following this tutorial so I added a new Class DataAccess but after I pasted the Public Shared Function GetConnectionString I get

Name 'ConfigurationManager' is not declared

Please advise.

Many thanks

PsychoCoder
Group Icon

10 Jan, 2009 - 10:20 AM

Post #4

You need to add a reference to the System.Configuration Namespace (sorry, I thought I went back in and added that so I apologize). To add this reference click "Project" on the menu bar (or "Website" I believe if this is a web application), then select "Add Reference", once the dialog opens scroll down (in the .Net Tab) until you see "System.Configuration", highlight that and hit OK. Then at the top of your code add the correct Import statement

CODE

Imports System.Configuration

Hope that helps

shavian

18 Jan, 2009 - 07:48 AM

Post #5

Yes it sorted out the problem.

I will continue using the tutorial now that I have returned from the slopes of Italy!

shavian

19 Jan, 2009 - 12:41 PM

Post #6

Now I'm a little confused about the HandleConnection method.

In the Select statement, if the connection is open, it is closed then re-opened.

However, in the functions you comment "..... Finally now close the connection.

Why is the connection re-opened in HandleConnection?

shotos

4 Mar, 2009 - 12:28 AM

Post #7

i have read but still do not understand why my code is not working
this is what i have done

Dim cn As OleDbConnection
Dim cmd As OleDbCommand
Dim dr As OleDbDataReader
Dim intaccount As Integer
Try
cn = New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\Administrator\My Documents\Visual Studio 2008\Projects\Account\accraeast_november.mdb")
'provider to be used when working with access database
cn.Open()
cmd = New OleDbCommand("SELECT Identity, Name, District FROM NorthEast_DB WHERE identity = '" & intaccount & "'", cn)
'cmd.ExecuteNonQuery()

dr = cmd.ExecuteReader
If dr.Read = True Then
Me.txtaccount = dr(0)
Me.txtname = dr(1)
Me.txtdistrict = dr(2)
' loading data into TextBoxes by column index
Else
MessageBox.Show("THIS MEMBER DOES NOT EXIST")

End If

Catch

End Try
dr.Close()this is what i have done but it is not working
it is not a function, i just want to get data from access data base into the text box using a parameter identity