public virtual void UpdateOne(T entity)
        {           
            Table<T> tbl = dbc.GetTable<T>();
            var q = from a in tbl where a == entity select a;
            T original = q.FirstOrDefault();            
            Utils.CopyObject(entity, original);            
            dbc.SubmitChanges();
        }

public static void CopyObject<T>(T from, T to)
        {
            Type tto = typeof(T);
            PropertyInfo[] pFrom = tto.GetProperties();            
            foreach (PropertyInfo p in pFrom)
            {
                PropertyInfo tmp = tto.GetProperty(p.Name);
                if (tmp == null) continue;
                tmp.SetValue(to, p.GetValue(from, null), null);
            }
        }

 var q = from a in tbl where a == entity select a;

public virtual void UpdateOne(T entity)
        {           
            Table<T> tbl = dbc.GetTable<T>();
            dbc.Attach(entity,true);
            dbc.SubmitChanges();
        }

public bool Save(tt_customer Customer)
{
    using ( TimeTrakkerContext context = new TimeTrakkerContext() )
    {
        try
        {
            if (Customer._version == null)
                context.tt_customers.Add(Customer);
            else
                context.tt_customers.Attach(Customer, true);

            context.SubmitChanges();
        }
        catch (Exception ex)
        {
            this.SetError(ex);
            return false;
        }
    }
    

    return true;
}

NorthwindDataContext db = new NorthwindDataContext();
Product product = db.Products.Single(p => p.ProductID == 1);
Console.WriteLine(product.CategoryID);
//Console.WriteLine(product.Category.CategoryName);
product.ProductName = product.ProductName + DateTime.Now.ToString();
NorthwindDataContext db2 = new NorthwindDataContext();
db2.Products.Attach(product, true);
db2.SubmitChanges();

IEnumerable<Person> people = ExecuteQuery<Person>(@"select ID, FirstName, LastName from people");

IEnumerable<Person> people = ExecuteQuery<Person>(@"update people set LastName = {1}  where ID = {0}", p.ID, p.LastName);

SQLDataContext dc = new SQLDataContext();
System.Data.Linq.ChangeSet cs = dc.GetChangeSet();
foreach(var p in cs.ModifiedEntries)
{
Person person = p as Person;
Console.WriteLine("{0} - {1} {2}", person.ID, person.FirstName, person.LastName);
}

UpdateCheck=UpdateCheck.Never

    public class detachableEntity<T> where T : detachableEntity<T>, new()
    {
        public void OnDataLoaded()
        {
            original = Clone();
        }
        public T original { get; set; }

        public T Copy()
        {
            return Copy((T)this);
        }
        public static T Copy(T Old)
        {
            T newItem = Clone(Old);
            newItem.OnDataLoaded(); // set the original state for the new object to the currect state 
            return newItem;
        }
        public T Clone()
        {
            return Clone((T)this);
        }
        public static T Clone(T item)
        {
            if (item == null)
                return null;

            T newItem = new T();
            // copy all subclass properties.
            foreach (PropertyInfo prop in item.GetType().GetProperties())
            {
                PropertyInfo prop2 = item.GetType().GetProperty(prop.Name);
                prop2.SetValue(newItem, prop.GetValue(item, null), null);
            }
            //the two items now share the same orginal state object, fix this by 
            //cloning the orginal state object on the item that to create a new original state
            //object for the new item
            if (item.original != null)
                newItem.original = item.original.Clone();
            return newItem;
        }
    }

            TimeTrakkerContext context = new TimeTrakkerContext();

            EntryEntity entry = context.EntryEntities.Where(ent => ent.Pk == 206).SingleOrDefault();
            entry.InvoicePk++;  // update a value

            context = null;  // clear out


            TimeTrakkerContext context5 = new TimeTrakkerContext();
            entry.Pk = entry.Pk;   //  force Pk IsVersion update

            context5.EntryEntities.Attach(entry, true);  // Attach still fails
            context5.SubmitChanges();

TimeTrakkerContext context = new TimeTrakkerContext();
EntryEntity entry = context.EntryEntities.Where(ent => ent.Pk == 206).SingleOrDefault();

EntryEntity entry = new EntryEntity();
entry.InvoicePk = int.Parse(txtEntry.Text);
TimeTrakkerContext context = new TimeTrakkerContext();
context.EntryEntities.Attach(entry, true);
context.SubmitChanges();

int pk = int.Parse(this.txtHiddenId.Text);
            
// *** Page level entity reference so we can bind against it
// *** Load with latest data from database
this.entry = customer.Context.CustomerEntities.SingleOrDefault(cust => cust.Pk == pk);

// *** Bind values from page back into entry entity
this.DataBinder.Unbind();

// *** Another field update
this.entry.Updated = DateTime.UtcNow;

// *** Related entity update
this.entry.User.LastEntryTime = DateTime.UtcNow;

// *** Save it
customer.Context.SubmitChanges();

        public bool InsertUpdateTest(RequestDTO reqDTO)
        {
            MYDBDataContext myDataContext = null;

            bool isSuccess = true;

            try
            {
                myDataContext = new MYDBDataContext(connStr);

                 my_request draft = null;

                 if (reqDTO.reqId > 0)
                 {
  draft = (from r in myDataContext.my_requests where   
        r.req_id == reqDTO.reqId  select r).Single();
                 }
                 else
                     draft = new my_request();// linq entity

            // one to many relationship    

                foreach (UserDTO user in reqDTO.users)
                {
                    my_userlink ml = new my_ userlink(); // linq entity
                    if (user.id > 0)
                    {
                        ml.user_id = user.id;
                        ml.originallySelected = true;
                        draft.my_userlinks.Add(ml);
                    }
                }

                if (reqDTO.reqId > 0)
                {
                    myDataContext.my_requests.Attach(draft,true);
                    myDataContext.SubmitChanges();
                }
                else
                {
                    myDataContext.my_requests.InsertOnSubmit(draft);
                    myDataContext.SubmitChanges();
                }

                
            }
            catch (Exception ex)
            {
                isSuccess = false;
                myCommon.InsertAppLog("NewRequest", 
                                 "Error",ex.ToString(), 1)            
             }
            finally
            {
                myDataContext.Dispose();
            }

            return isSuccess;

        }

datacontext dc = new datacontext();
product p = dc.products.single(p=> p.id == 1);
dc = null;

product pToUpdate = new product(){.id = p.id, .name = p.name};

//do stuff within the same HTTP call

datacontext dc2 = new datacontext();
datacontext dc3 = new datacontext();

product pOriginal = dc3.products.single(p=> p.id == 1);

dc2.products.Attach(pToUpdate,pOriginal);
dc2.SubmitChanges();

datacontext dc = new datacontext();
product p = dc.products.single(p=> p.id == 1);
dc = null;

//do stuff within the same HTTP call

datacontext dc2 = new datacontext();
datacontext dc3 = new datacontext();

product pOriginal = dc3.products.single(p=> p.id == 1);

dc2.products.Attach(p,pOriginal);
dc2.SubmitChanges();

An attempt has been made to Attach or Add an entity that is not new,
perhaps having been loaded from another DataContext.
This is not supported.

Customer customer;
Order order;
 
using (var context = new SomeDataContext()) {
 
    // Just get the first, doesn't matter when playing!
    customer = context.Customers.First();
}
 
order = new Order();
order.Reference = "OrderRef";
order.Customer = customer;
 
using (var context = new SomeDataContext()) {
 
    // Doesn't work if you use InsertOnSubmit(), or any other Attach() overload.
    context.Orders.Attach(order);
    context.SubmitChanges();
}

        public T Save(T item)
        {
            // Does it exist?
            T existingItem = Table.FirstOrDefault(i => i == item);
 
            if (existingItem == null) // Insert (new)
            {
                Table.InsertOnSubmit(item);
            }
            else // Update (exists)
            {
                // Copy all changed [ColumnAttribute] property values to existing object in Linq Context
                item.GetType().GetProperties()
                    .Where(p => p.GetCustomAttributes(typeof(ColumnAttribute), false).Any())
                    .ToList()
                    .ForEach(p => p.SetValue(existingItem, p.GetValue(item, null), null));
            }
 
            Context.SubmitChanges();
            FinalizeQuery();
 
            return item;
        }