Join LINQ queries from multiple contexts - linq

Question

I am trying to create a ViewModel for data that I want to display in my view. The issue is, the data being displayed is spread across 2 databases and multiple tables within each. I've read that you cannot join Linq queries across multiple contexts, which makes sense, and I've also read that we can't use Code-First in EF5 to use Stored Procedures....which led me to using 3 different Linq queries and attempt to combine them into 1 ViewModel...I'm just not sure how to get there.
Here's my Linq queries:
var csdContext = new CSDContext(CustomerCode);
var masterContext = new MasterContext();
//Only returns 1 row - which is what we want.
List<Site> sites = (from s in csdContext.Sites
join sa in csdContext.SiteAddresses
on s.SiteID equals sa.SiteID
join a in csdContext.Addresses
on sa.AddressID equals a.AddressID
join spv in csdContext.SiteProductVersions
on s.SiteID equals spv.ProductVersionID
where s.SiteID == id
select s).ToList();
//List
List<States> states = (from s in masterContext.StatesTable
select s).ToList();
My ViewModel looks like this:
public class SiteDetailsViewModel
{
public string Address { get; set; }
public string Address2 { get; set; }
public string City { get; set; }
public string StateCode { get; set; }
public string ZipCode { get; set; }
public string OfficePhone { get; set; }
public string MobilePhone { get; set; }
public string AlternativePhone { get; set; }
public int ProductVersionID { get; set; }
}
Basically, I need the following data from these tables:
csdContext - Address
Address
Address2
City
ZipCode
csdContext - Sites
OfficePhone
MobilePhone
AlternativePhone
csdContext - SiteProductVersions
ProductVersionID
masterContext - States
StateCode
Here's how the tables are joined in SQL:
SELECT csd_a.Address, csd_a.Address2, csd_a.City, mstr_st.StateCode, csd_a.ZipCode, csd_s.OfficePhone, csd_s.MobilePhone,
csd_s.AlternativePhone, csd_spv.ProductVersionID
FROM CSD.dbo.Sites AS csd_s
INNER JOIN CSD.dbo.SiteAddress AS csd_sa ON csd_sa.SiteID = csd_s.SiteID
INNER JOIN CSD.dbo.Address AS csd_a ON csd_a.AddressID = csd_sa.AddressID
INNER JOIN CSD.dbo.SiteProductVersions AS csd_spv ON csd_s.SiteID = csd_spv.SiteID
INNER JOIN MasterDB.dbo.States AS mstr_st ON mstr_st.StateID = csd_a.StateID
I can't figure out how to merge these 3 results to create the ViewModel data for SiteDetailsViewModel. Can anyone help?

Answer 1

If you materialize your queries as described in OP you can use this:
var query = sites.Join(
states,
si => si.StateID,
st => st.StateID,
(si, st) => new SiteDetailsViewModel
{
Address = si.Address,
Address2 = si.Address2,
City = si.City,
StateCode = st.StateCode,
ZipCode = si.ZipCode,
OfficePhone = si.OfficePhone,
MobilePhone = si.MobilePhone,
AlternativePhone = si.AlternativePhone,
ProductVersionID = siProductVersionID
});

Answer 2

One possible alternate solution is to create views in DB #2 of the tables in DB #1. Then you can model/map those views in EF for DB #2. You would of course still need a context for DB #1 if you need to update any of the tables. But the benefit of this solution is that you can do all of your read access on a single context and get joins at the server instead of in memory.

Answer 3

So why don't you write it like this:
from ...
...
where s.SiteID == id
select new SiteDetailsViewModel()
{
Address = sa.Address,
Address2 = as.Address2,
..
}