Lambda表達式和實體框架，如何獲取對另一個方法創建的對象的引用

Question

SO，我有我的ef模型的以下初始化程序。

爲了簡化，我有一個車輛，一個客戶，一個地址實體。 我用一種方法創建了地址實體。 現在我需要創建客戶實體，但是如何將地址值分配給現有對象？

public class DevelopmentInitializer 
    { 
     /// <summary> 
     /// This class allows the database tables to be created and seed at runtime. 
     /// </summary> 
     public class AskAndTrackInitializer : DropCreateDatabaseAlways<AskAndTrackContext> 
     { 
      /// <summary> 
      /// This fills the database with sample data to start with 
      /// </summary> 
      /// <param name="context">DBContext required for the connection</param> 
      protected override void Seed(AskAndTrackContext context) 
      { 
       BuildDealers(context); 
       BuildRequesters(context); 
       BuildAddresses(context); 
       BuildCustomers(context); 
       BuildVehicles(context); 

       BuildWorkflowsBase(context); 
      } 

      private void BuildDealers(AskAndTrackContext context) 
      { 
       var dealer1 = new Dealer {DealerId = 1, Name = "Dealer 1"}; 
       var dealer2 = new Dealer { DealerId = 2, Name = "Dealer 2" }; 
       var dealer3 = new Dealer { DealerId = 3, Name = "Dealer 3" }; 
       var dealer4 = new Dealer { DealerId = 4, Name = "Dealer 4" }; 
       var dealer5 = new Dealer { DealerId = 5, Name = "Dealer 5" }; 

       context.Dealers.Add(dealer1); 
       context.Dealers.Add(dealer2); 
       context.Dealers.Add(dealer3); 
       context.Dealers.Add(dealer4); 
       context.Dealers.Add(dealer5); 

      } 

      /// <summary> 
      /// Requesters test data 
      /// </summary> 
      private void BuildRequesters(AskAndTrackContext context) 
      { 
       var requester1 = new Requester {EmailAddress = "le.xx@hotmail.com", Name="Andres x", RequesterId=1}; 
       var requester2 = new Requester { EmailAddress = "le.xxx@hotmail.com", Name = "Andres y", RequesterId = 2 }; 
       var requester3 = new Requester { EmailAddress = "le.yyy@hotmail.com", Name = "Juan l", RequesterId = 3 }; 
       var requester4 = new Requester { EmailAddress = "le.zzzz@hotmail.com", Name = "Peter x", RequesterId = 4 }; 
       var requester5 = new Requester { EmailAddress = "le.aaaa@hotmail.com", Name = "Patrick z", RequesterId = 5 }; 

       context.Requesters.Add(requester1); 
       context.Requesters.Add(requester2); 
       context.Requesters.Add(requester3); 
       context.Requesters.Add(requester4); 
       context.Requesters.Add(requester5); 

      } 

      /// <summary> 
      /// Workflow base test data and its related objects 
      /// </summary> 
      private void BuildWorkflowsBase(AskAndTrackContext context) 
      { 

      } 

      /// <summary> 
      /// Vehicle test data 
      /// </summary> 
      private void BuildVehicles(AskAndTrackContext context) 
      { 
       //var vehicle1 
      } 

      /// <summary> 
      /// Customers test data 
      /// </summary> 
      private void BuildCustomers(AskAndTrackContext context) 
      { 
       //var customer1 = new Customer{Address = ??? 


      } 

      private void BuildAddresses(AskAndTrackContext context) 
      { 
       var address1 = new Address 
            { 
             AddressId = 1, 
             Box = "71", 
             City = "Antwerp", 
             Number = "1", 
             Street = "Belgielei", 
             Zip = "2018" 
            }; 

       var address2 = new Address 
            { 
             AddressId = 2, 
             Box = "21", 
             City = "Antwerp", 
             Number = "1", 
             Street = "Lange Leemstraat", 
             Zip = "2018" 
            }; 

       var address3 = new Address 
            { 
             AddressId = 3, 
             Box = "23", 
             City = "Antwerp", 
             Number = "1", 
             Street = "Lamoriniestraat", 
             Zip = "2018" 
            }; 

       var address4 = new Address 
            { 
             AddressId = 4, 
             Box = "24", 
             City = "Antwerp", 
             Number = "1", 
             Street = "De Keyserlei", 
             Zip = "2000" 
            }; 

       var address5 = new Address 
            { 
             AddressId = 5, 
             Box = "34", 
             City = "Antwerp", 
             Number = "1", 
             Street = "Italialei", 
             Zip = "2020" 
            }; 

       context.Addresses.Add(address1); 
       context.Addresses.Add(address2); 
       context.Addresses.Add(address3); 
       context.Addresses.Add(address4); 
       context.Addresses.Add(address5); 

      } 
     } 

Answer 1

在EF代碼首先，你必須聲明兩個實體在partent實體宣告孩子的實體的列表之間的關係

public List<ChildeEntity> ChildEntities { get; set; } 

然後，如果你創建一個ChildEntity：

var newChild = new ChildEntity(); 

和您將其添加到父實體列表中：

parentEntity.ChildEntities.Add(newChild); 

如果父母en tity在上下文中，newChild將自動置於上下文中，並且當您發生更改時，在將更改保存到數據庫之前，將在newChild中設置子項的必要屬性（FK屬性）。

所以，答案是：只需將其添加到父級的列表。

其實關係可表示有3種方式：

• 父母的兒童實體
• 在指向父
• 一個FK子實體屬性的列表（可是否包含在實體中）

如果您在上下文中工作，則無論何時更改3個屬性中的任何一個，都會相應地更正其他屬性。

所以答案可以包括更改任何其他屬性。

Answer 2

我看到兩個選項：（沒有無關lambda表達式;）

1. 您還可以從內部BuildAdressesBuildCustomers;

   private void BuildAddresses(AskAndTrackContext context) 
   { 
       var listAddress = new List<Address>(); 
       // create adresses, populate listAdress with the Address objects. 
       BuildCustomers(AskAndTrackContext context, listAddress); 
   } 
   

2. BuildAdresses可以返回ID的列表，並且您傳遞列表作爲參數傳遞給BuildCustomers。

   List<Address> addresses = BuildAddresses(context); 
   BuildCustomers(context, addresses); 
   

不要忘記調用context.SaveChanges()在每個填充功能的結束。這樣Entity會知道你傳遞的對象是表中的一個元素。

兩種解決方案都會做同樣的事情，但可讀性會有所不同。