如何在LINQ

Question

返回連接語句我想結果3返回到主方法

var result = (from od in orders 
     join em in employees on od.EmployeeID equals em.EmployeeID 
     join ct in customers on od.CustomerID equals ct.CustomerID 
     //orderby em.EmployeeID 
     select new 
     { 
      od.OrderID, 
      od.ShipCountry, 
      ct.CompanyName, 
      ct.ContactName, 
      FullName = em.FirstName + ' '+ em.LastName, 
     }); 


var newOrders = result.OrderBy("OrderID DESC"); 

var result3 = newOrders 
    .ToList() 
    .Skip(rowsPerPage * (page-1)) 
    .Take(rowsPerPage); 

return result3; 
} 

public class MyJoin { 
public int OrderID { get; set; } 
public DateTime OrderDate { get; set; } 
public string ShipCountry { get; set; } 
public string CompanyName { get; set; } 
public string ContactName { get; set; } 
public string EmployeeName { get; set; } 
} 

我不知道如何將它返回一個簡單的

return result3; 

不做的伎倆，我得到一個錯誤

不能隱式類型轉換 System.Collections.Generic.List<AnonymousType#1>到 System.Collections.Generic.List<UserQuery.MyJoin>

Answer 1

這不是在這裏，因爲工作：

select new 
{ 
    od.OrderID, 
    od.ShipCountry, 
    ct.CompanyName, 
    ct.ContactName, 
    FullName = em.FirstName + ' '+ em.LastName, 
} 

你正在創造新的類型 - > AnonymouseType，這是不是MyJoin類型，你期待你的函數返回。簡單使用：

select new UserQuery.MyJoin 
{ 
    OrderID = od.OrderID, 
    ... 
} 

當然你需要填寫從MyJoin類的字段。

Answer 2

您不能從函數調用中返回匿名類型。

你必須明確定義您希望無論如何（）不需要.ToList（）類型，然後

var result = (from od in orders 
    join em in employees on od.EmployeeID equals em.EmployeeID 
    join ct in customers on od.CustomerID equals ct.CustomerID 
    //orderby em.EmployeeID 
    select new UserQuery.MyJoin 
    { 
     od.OrderID, 
     od.ShipCountry, 
     ct.CompanyName, 
     ct.ContactName, 
     FullName = em.FirstName + ' '+ em.LastName, 
    }); 


var newOrders = result.OrderBy("OrderID DESC"); 

var result3 = newOrders 
.Skip(rowsPerPage * (page-1)) 
.Take(rowsPerPage); 
.ToList() 

return result3; 

請注意，您不需要兌現的結果，如果這是LINQ到對象，或如果DbContext對調用者可用。

Answer 3

指定型 -

在你的情況

IQueryable<UserQuery.MyJoin> result = (from od in orders 
    join em in employees on od.EmployeeID equals em.EmployeeID 
    join ct in customers on od.CustomerID equals ct.CustomerID 
    //orderby em.EmployeeID 
    select new UserQuery.MyJoin 
    { 
     od.OrderID, 
     od.ShipCountry, 
     ct.CompanyName, 
     ct.ContactName, 
     FullName = em.FirstName + ' '+ em.LastName, 
    });