ASP.NET MVC類繼承和LINQ

Question

我遇到了LINQ到我已解決的實體問題，但希望確保以正確的方式解決問題。

我有2類：

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 
        ); 
     } 
    } 
} 

} 

當LINQ查詢，我原來試過：

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(); 

但是我一直得到錯誤「實體或複雜類型「ShopTest.Controllers.Shops '不能構建一個LINQ to Entities查詢「

我已經解決了以下代碼的問題，但它沒有任何意義，爲什麼這將工作 - 對MVC是新的我希望有人可以探討就是它。 :-)

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(); 

我這樣做是否正確？有沒有更好的辦法？

Answer 1

EF有限制，您無法在查詢中手動創建映射實體。這意味着你不能這樣做：

var shops = from s in db.Shops where ... select new Shop { ... }; 

這也涉及派生實體。因此，你首先必須調用ToList切換到LINQ到對象：

var shopse = db.Shops.Where(...).ToList().Select(s => new Shop { ... }); 

一般來說，你應該確定有：

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();