代碼第一次添加多對多關係的實體

Question

我有一個對象客戶可以有多個客戶類型，每個客戶類型可以有多個客戶。我是EF的新手，但設法添加了一位客戶，但似乎無法獲得添加客戶的客戶類型的語法。

我的客戶類（簡體）：

public partial class Customer 
{ 
     public virtual int Id { get; set;} 
     public virtual string Name { get; set;} 

    #region Navigation Properties 

     public virtual ICollection<CustomerType> CustomerTypes 
     { get; set; } 

    #endregion 
} 

客戶類型：

public partial class CustomerType 
{ 

     public virtual int Id 
     { 
      get; 
      set; 
     } 

     public virtual string Name 
     { 
      get; 
      set; 
     } 

     #region Navigation Properties 

     public virtual ICollection<Customer> Customers 
     { get; set; } 

     #endregion 
} 

當我運行這個項目CustomerTypeCustomer表與列CUSTOMER_ID和CustomerType_Id創建的，因此，這是好的。

我然後創建客戶像這樣：

// code behind 
var customer = new Customer(); 
customer.name = txtCustomerName.Text; 

using (var context = new MyEntities()) 
{ 
    context.Customers.Add(customer); 
    context.SaveChanges(); 
} 

我這裏Insert/Update Many to Many Entity Framework . How do I do it?看了一下，並試圖做類似的客戶類型的東西：

var customer = new Customer(); 
customer.name = txtCustomerName.Text; 

// only starting with one customer type selected in a check box list 
CustomerType customerType = context.CustomerTypes.FirstOrDefault(i => i.Id == 1); 

using (var context = new MyEntities()) 
{ 
    // IncidentTypes throws Object reference not set to an instance of an object 
    customer.CustomerTypes.add(customerType); 

    context.Customers.Add(customer); 
    context.SaveChanges(); 
} 

我失去的東西在這裏很明顯？

在此先感謝。

編輯：由於某種原因，我只。新增（無AddToObject，AttachTo等

Answer 1

必須初始化CustomersTypes收集第一

customer.CustomerTypes = new List<CustomerType>(); 

您也可以此初始化添加到您的Customer的。 。構造

Answer 2

這是做這件事：

var customer = new Customer(); 
customer.name = txtCustomerName.Text; 

// only starting with one customer type selected in a check box list 
//add Include there 
CustomerType customerType = context.CustomerTypes.Include("Customers").FirstOrDefault(i => i.Id == 1); 

using (var context = new MyEntities()) 
{ 
    // IncidentTypes throws Object reference not set to an instance of an object 
    //customer.CustomerTypes.add(customerType); 

    //context.Customers.Add(customer); 
    customerType.Customers.Add(customer); 
    context.SaveChanges(); 
}