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Difficulty listing data using a view model in ASP.NET MVC

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.

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();

The type of one of the expressions in the join clause is incorrect in Entity Framework. Constant in left join

I'm trying to do a left join in an EF query. I'm getting the following error:
Error CS1941 The type of one of the expressions in the join clause is
incorrect. Type inference failed in the call to 'GroupJoin'
and here is the C# code:
var foo = from m in db.ClientMasters
join a in db.Orders on new { m.Id, Status = "N" } equals new { a.ClientID, a.Status } into a_join
from a in a_join.DefaultIfEmpty()
select new { m.ClientID, a.ID };

The column names have to match in the join; here is the corrected code:
var foo = from m in db.ClientMasters
join a in db.Orders on new { ClientID = m.Id, Status = "N" } equals new { a.ClientID, a.Status } into a_join
from a in a_join.DefaultIfEmpty()
select new { ClientID = m.Id, OrderId = a.Id };

using ToString() in linq expression to convert DateTime value

I'm trying to convert a DateTime value to a string, but I'm getting this runtime error:
Additional information: LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be
translated into a store expression.
This is the query I'm using:
using (var db = new DbContext())
{
var results = (from u in db.AspNetUserses
join upi in db.UserPersonalInfoes on u.Id equals upi.UserId into upis
from upi in upis.DefaultIfEmpty()
join up in db.UserPreferenceses on u.Id equals up.UserId into ups
from up in ups.DefaultIfEmpty()
join us in db.UserStatses on u.Id equals us.UserId into uss
from us in uss.DefaultIfEmpty()
select new
{
Username = u.UserName,
Telephone = (upi == null ? String.Empty : upi.Telephone),
ID = u.Id,
LastLogin = (us == null ? String.Empty : us.LastLoginDate)
}).ToList();
gvUsers.DataSource = results;
gvUsers.DataBind();
}
Any idea how can I fix this error?

Create a second list and do the transformation there.
using (var db = new DbContext())
{
var results = (from u in db.AspNetUserses
join upi in db.UserPersonalInfoes on u.Id equals upi.UserId into upis
from upi in upis.DefaultIfEmpty()
join up in db.UserPreferenceses on u.Id equals up.UserId into ups
from up in ups.DefaultIfEmpty()
join us in db.UserStatses on u.Id equals us.UserId into uss
from us in uss.DefaultIfEmpty()
select new
{
Username = u.UserName,
Telephone = (upi == null ? String.Empty : upi.Telephone),
ID = u.Id,
LastLogin = (us == null ? DateTime.MinValue : us.LastLoginDate)
}).ToList();
var list = (from r in results
select new {
Username = r.UserName,
Telephone = r.Telephone,
ID = r.ID
LastLogin = r.LastLogin == DateTime.MinValue ? "" : r.LastLogin.ToString()
}).ToList();
gvUsers.DataSource = list;
gvUsers.DataBind();
}

LINQ query with List<> and asking if is null

I have some method with linq query. Logic is next, if I pass null for list of role ids, I want all roles to be included in process, but if it has value, I want only those with id in the list. I am receiving exeption.
public static List<NameEmail> GetNameEmailPairs(Guid guid, List<int> recipientRoles)
{
using (var tc = TransactionContext())
{
var dc = tc.DataContext;
var nameEmailPairs = (
from email in dc.Emails
join logon in dc.Logons on email.GUID equals logon.GUID
join eLogon in dc.ELogons on logon.UID equals eLogon.LogonGUID
join role in dc.Roles on entityLogon.PrimaryPermissionRoleID equals role.RoleID
where
(recipientRoles == null || recipientRoles.Contains(role.RoleID))
select new NameEmail
{
Email = email.EmailAddress,
FullName = GetName(logon.GUID)
}
)
.ToList();
return nameEmailPairs;
}
}
This part is breaking (recipientRoles == null || recipientRoles.Contains(role.RoleID)). Can you please help me with this, what should I do?

To make debugging easier, break your query up into pieces like this:
var nameEmailPairs = (
from email in dc.Emails
join logon in dc.Logons on email.GUID equals logon.GUID
join eLogon in dc.ELogons on logon.UID equals eLogon.LogonGUID
join role in dc.Roles on entityLogon.PrimaryPermissionRoleID equals role.RoleID
select new {email, role}
);
if(recipientRoles != null)
{
nameEmailPairs = nameEmailPairse.Where(
recipientRoles.Contains(p => p.role.RoleID)
);
}
var nameEmailPairs = (from p in nameEmailPairs
select new NameEmail
{
Email = email.EmailAddress,
FullName = GetName(logon.GUID)
}).ToList();

Linq to SQL with Group by

I am trying to convert this T-SQL to a Linq To SQL but can't work out the group by aggregate functions. Any help welcome.
select c.ClientID, GivenName, Surname, max(a.Address), max(t.Value)
from Client c
left join ClientAddress a on c.ClientID = a.ClientID
left join ClientContact t on c.ClientID = t.ClientID
group by c.ClientID, GivenName, Surname

To group by a composite key, you typically use an anonymous type:
var qry = from x in someSource
group x by new { x.ClientID, x.GivenName, x.Surname } into grp
select new { grp.Key, Address = grp.Max(x => x.Address),
Value = grp.Max(x => x.Value) };

The exact answer I came up with was
public IQueryable<ClientSearchDTO> GetClientsDTO()
{
return (from client in this.Context.Clients
join address in this.Context.ClientAddresses on client.ClientID equals address.ClientID
join contact in this.Context.ClientContacts on client.ClientID equals contact.ClientID
where contact.ContactType == "Phone"
group client by new { client.ClientID, client.Surname, client.GivenName } into clientGroup
select new ClientSearchDTO()
{
ClientID = clientGroup.Key.ClientID,
Surname = clientGroup.Key.Surname,
GivenName = clientGroup.Key.GivenName,
Address = clientGroup.Max(x => x.ClientAddresses.FirstOrDefault().Address),
PhoneNumber = clientGroup.Max(x => x.ClientContacts.FirstOrDefault().Value)
});
}