ASP.NET MVC类继承和LINQ

Question

我遇到了LINQ到我已解决的实体问题，但希望确保以正确的方式解决问题。

我有2类：

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 
        ); 
     } 
    } 
} 

} 

当LINQ查询，我原来试过：

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(); 

但是我一直得到错误“实体或复杂类型“ShopTest.Controllers.Shops '不能构建一个LINQ to Entities查询“

我已经解决了以下代码的问题，但它没有任何意义，为什么这将工作 - 对MVC是新的我希望有人可以探讨就是它。 :-)

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(); 

我这样做是否正确？有没有更好的办法？

Answer 1

EF有限制，您无法在查询中手动创建映射实体。这意味着你不能这样做：

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

这也涉及派生实体。因此，你首先必须调用ToList切换到LINQ到对象：

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

一般来说，你应该确定有：

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();