ASP.NET MVC class inheritence and LINQ - entity-framework

Question

I'm having a problem with LINQ to entities which I've resolved, but want to make sure I've resolved in the right way.
I have 2 classes:
namespace ShopTest.Models
{
public class Shop
{
public int ShopID { get; set; }
public string Name { get; set; }
public string Address1 { get; set; }
public string Address2 { get; set; }
public string City { get; set; }
public string State { get; set; }
public string Postcode { get; set; }
public string Country { get; set; }
public decimal Latitude { get; set; }
public decimal Longitude{ get; set; }
}
[NotMapped]
public class ShopLocation : Shop
{
public decimal AddressLatitude { get; set; }
public decimal AddressLongitude { get; set; }
public decimal DistanceFromAddress
{
get
{
return Convert.ToDecimal(
Math.Sqrt(
Math.Pow(Convert.ToDouble(this.Latitude - this.AddressLatitude), 2.0)
+
Math.Pow(Convert.ToDouble(this.Longitude- this.AddressLongitude), 2.0)
)
* 62.1371192
);
}
}
}
}
When querying in LINQ, I originally tried:
decimal lat = Convert.ToDecimal(-33.8736510, NumberFormatInfo.InvariantInfo);
decimal lng = Convert.ToDecimal(151.2068896, NumberFormatInfo.InvariantInfo);
var nearbyShops = from c in db.Shops
where Math.Abs(c.lat - lat) < 0.25M &&
Math.Abs(c.lng - lng) < 0.25M
select new NearbyShopLocation()
{
StoreNumber = store.StoreNumber,
Address = store.Address,
City = store.City,
Region = store.Region,
CountryCode = store.CountryCode,
PostalCode = store.PostalCode,
Latitude = store.Latitude,
Longitude = store.Longitude,
AddressLatitude = lat,
AddressLongitude = lng
};
var nearbySortedShops = nearbyShops.ToList().OrderBy(s => s.DistanceFromAddress).ToList();
However I kept getting the error "The entity or complex type 'ShopTest.Controllers.Shops' cannot be constructed in a LINQ to Entities query"
I've fixed the issue with the below code, but it doesn't make sense why this would work - being new to MVC I'm hoping someone can explain it. :-)
var nearbyShops = (from c in db.Shops
where Math.Abs(c.lat - lat) < 0.25M &&
Math.Abs(c.lng - lng) < 0.25M
select new
{
StoreNumber = c.StoreNumber,
Address = c.Address,
City = c.City,
Country = c.Country,
PostalCode = c.PostalCode,
Latitude = c.Latitude,
Longitude = c.Longitude,
}).ToList().Select(l => new ShopLocation
{
Name = l.Name,
City = l.City,
State = l.State,
Country = l.Country,
Lat = l.Lat,
Lng = l.Lng,
AddressLatitude = lat,
AddressLongitude = lng
}).ToList().OrderBy(s => s.DistanceFromAddress).ToList();
Have I done this correctly? Is there a better way?

Answer 1

EF has limitation that you cannot build mapped entity manually in the query. That means you cannot do this:
var shops = from s in db.Shops where ... select new Shop { ... };
This also involves derived entities. Because of that you first have to call ToList to switch to Linq-to-Objects:
var shopse = db.Shops.Where(...).ToList().Select(s => new Shop { ... });
Generally you should be OK with:
var nearbyShops =
(from c in db.Shops
where Math.Abs(c.lat - lat) < 0.25M &&
Math.Abs(c.lng - lng) < 0.25M
select c).ToList()
.Select(l => new ShopLocation
{
Name = l.Name,
City = l.City,
State = l.State,
Country = l.Country,
Lat = l.Lat,
Lng = l.Lng,
AddressLatitude = lat,
AddressLongitude = lng
}).OrderBy(s => s.DistanceFromAddress).ToList();