that's my code (data access layer, im using linq to sql)

 public class ClientDAO : IClient
    {
        private static DataClassesDataContext db;
        
       
        #region Constructeur

        public ClientDAO()
        {
            try
            {
                ConnectionStringSettings settings;
                settings = ConfigurationManager.ConnectionStrings["Gestion_flotteConnectionString1"];
                db = new DataClassesDataContext(settings.ConnectionString);
            }
            catch (NullReferenceException) { }
        }
        #endregion

        #region CRUD
       

        public bool ModifierClient(client oClient)
        {


            ChangeSet changeset = null;
            int changeCount = 0;
            
                db.client.Attach(oClient);

                changeset = db.GetChangeSet();

                changeCount = changeset.Updates.Count;

                db.SubmitChanges();

            
            if (changeCount > 0) { return true; }

            else { return false; }
        }

 and my business class :

public class Clientbusiness : IClientbusiness
    {
       #region Données privées de la classe
        private IClient _iClient;
        #endregion

        #region Constructeur
        public Clientbusiness()
        {
            _iClient = new ClientDAO();
        }

        #endregion

        #region Getter and Setter
        public IClient IClient
        {
            get { return this._iClient; }
            set { this._iClient = value; }
        }
        #endregion

        #region Methode Business
        
        #region Operation CRUD
       
        public bool ModifierClient(client oClient)
        {
            return _iClient.ModifierClient(oClient);
        }

  and finally my code behind *.aspx.cs

 protected void charger()
    {
        oEntreprise = (entities.entreprise) HttpContext.Current.Session[IDvariable];
        oClient = iclientbusiness.GetClientByIdClient(oEntreprise.id_client);
        Textloginclient.Text = oClient.login_client;
        Textnomclient.Text = oClient.nom_client;
        Textprenomclient.Text = oClient.prenom_client;
        Textpswdclient.Text = oClient.pswd_client.ToString(); ;
        Textemailclient.Text = oClient.email_client;
        Texttelclient.Text = oClient.tel_client.ToString();
        Textadresseentreprise0.Text = oEntreprise.adresse_entreprise;
        Texttelentreprise.Text = oEntreprise.telephone_entreprise.ToString();
        Textnomentreprise.Text = oEntreprise.nom_entreprise;
    }
    protected void enregister()
    {
        oClient.nom_client = Textnomclient.Text;
        oClient.prenom_client = Textprenomclient.Text;
        oClient.pswd_client = FormsAuthentication.HashPasswordForStoringInConfigFile(Textpswdclient.Text,"MD5");
        oClient.email_client = Textemailclient.Text;
        oClient.tel_client = int.Parse(Texttelclient.Text);
        oClient.login_client = Textloginclient.Text;
        oEntreprise.telephone_entreprise = ientreprisebbusiness.GetEntrepriseByIdClient(oClient.id_client).telephone_entreprise;
        oEntreprise.nom_entreprise = ientreprisebbusiness.GetEntrepriseByIdClient(oClient.id_client).nom_entreprise;
        oEntreprise.adresse_entreprise = ientreprisebbusiness.GetEntrepriseByIdClient(oClient.id_client).adresse_entreprise;
        oEntreprise.nom_entreprise = Textnomentreprise.Text;
        oEntreprise.adresse_entreprise = Textadresseentreprise0.Text;
        oEntreprise.telephone_entreprise = int.Parse(Texttelentreprise.Text);
        iclientbusiness.ModifierClient(oClient);
        ientreprisebbusiness.ModifierEntreprise(oEntreprise);
        

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        this.enregister();
        Response.Redirect("loginadministrateur.aspx",false);
    }

  i have problem with  the method "enregister" in aspx.cs, when i start  the debug , i got this exception :"invalidOperationException:  Cannot attach an entity that already exists" in    the class ClientDAO : ( i dont understand why as i try to update this entity)

any ideas??

thanks 

I assume that somehow charger is called before enregister is called which sets the global(?) variable called oClient.  From the method name, GetClientByIdClient, I also guess that you are retrieving oClient from the database.  If these things are true (and the error message you quote implies this) then you should not Attach this client back to the database as it is already attached. 

The fix should be easy, remove the line from ClientDAO.ModifierClient which does the attach.

 hi, you're right, but how can  I update (edit) the entity oClient  if I  remove the line which does the attach in clientDao.modifierclient?

because; i think , ill need a methode that assure the update of this entity??

I'm just curious what would happen if you made your datacontext an instance member rather than static? The datacontext is not meant to be a long lived object and I am guessing that by having it static, the change tracking is getting screwy when you are attaching and detaching.

 Take a peek at this link: LINQ to SQL ObjectTrackingEnabled and Deferred Loading of Related Data

  i change the instance of datacontext, (i removed static) ,

but i still have this error  when i start the debug :

An entity can only be attached as modified without original state if it declares a version member or does not have an update check policy ??

any ideas , ?????

Well, I'm guessing that you do not have a timestamp column in your table?

 The solution to this is, as silly as it may seem, to add a timestamp in Sql to the table.

This link should explain it in detail:

http://geekswithblogs.net/michelotti/archive/2007/12/17/117791.aspx

ive tried timestamp, but i have tables which are associated  to this table,

si it doesn't work, i got an  article which talk about tthat, and even if we add a timestamp in the other tables , it doesn't resolve the problem!!

:(

thanks 

Have you removed the Attach?  LinqToSql will keep track of the changes to your objects.

 i tried it but the update doesnt work!!!

 The only way to get around this problem is to create a new DataContext just before you do the Attach and not use a global DataContext.

I haven't found any other way, I would rather use a global context but it causes too many problems like this.