在ASP.NET MVC中使用视图模型很难列出数据

Question

I am trying to pass data from a view model which derives from 2 models. The controller looks like this

public ActionResult SessionDetails()
{
    var Sessions = (from a in db.Appointments
                    join c in db.Clients
                    on a.clientid equals c.id into SessionList
                    from c in SessionList.DefaultIfEmpty()
                    select new SessionViewModel()
                    {

                        id = a.id,
                        sessionnotes = a.sessionnotes,
                        firstname = c.firstname,
                        date = a.date,

                    }).ToList()
             .Select(x => new SessionViewModel()
             {

                 id = a.id,
                 sessionnotes = a.sessionnotes,
                 firstname = c.firstname,
                 date = a.date,
             });

    return View(Sessions);
}

It is coming up with errors saying the name "a" does not exist in the current context? Any ideas as to what is going on?

I am really new to this, I followed these instructions using website http://techfunda.com/howto/262/list-data-using-viewmodel which does what I want SessionDetails to do.

I already have a view for this.

UPDATE

I have made following changes:

public ActionResult SessionDetails()
{
    var Sessions = (from a in db.Appointments
                    join c in db.Clients
                    on a.clientid equals c.id into SessionList
                    from c in SessionList.DefaultIfEmpty()
                    select new SessionViewModel()
                    {

                        id = a.id,
                        sessionnotes = a.sessionnotes,
                        firstname = c.firstname,
                        date = a.date,

                    }).ToList();


    return View(Sessions);
}

But when i run it, i get this: an exception of type System.NotSupportedException occurred in EntityFramework.SqlServer.dll but was not handled in user code.

Additional information: the entity or complex type fypag.Models.SessionViewModel cannot be constructed in a LINQ to Entities query.

Answer 1

I think your model should look like this.

   var Sessions = (from a in db.Appointments
                             join c in db.Clients
                             on a.clientid equals c.id into SessionList
                             from c in SessionList.DefaultIfEmpty()
                             select new SessionViewModel()
                             {

                                id = a.id,
                                 sessionnotes = a.sessionnotes,
                                 firstname = c.firstname,
                                 date = a.date,

                             }).ToList()
                   .Select(x => new SessionViewModel()
                    {
                         id = x.id,
                         sessionnotes = x.sessionnotes,
                         firstname = x.firstname,
                         date = x.date,
                    });

UPDATE:

var Sessions = (from a in db.Appointments
                join c in db.Clients
                on a.clientid equals c.id into SessionList
                from c in SessionList.DefaultIfEmpty()
                .Select(y => new SessionViewModel()
                {
                    id = y.id,
                    sessionnotes = y.sessionnotes,
                    firstname = y.firstname,
                    date = y.date,

                }).ToList();