如何：加入使用LINQ三个列表对象

Question

问题是不被输出

  using System; 
      using System.Collections.Generic; 
      using System.Linq; 
      using System.Text; 

      namespace LinqToObjects 
      { 
      class Program 
      { 
    static void Main(string[] args) 
    { 
     var customers = Customer.GetAllCustomers(); 
     var addresses = Address.GetAllAddresses(); 
     var addressRelations = AddressRelation.GetAllAddressRelations(); 

     var results = customers 
        .Join(addressRelations, 
        c => c.CustomerID, 
        ar => ar.CustomerID, 
        (c, ar) => new 
        { 
         CustomerName = c.FirstName + " " + c.LastName, 
         CustomerID = c.CustomerID, 
         AddressRelID = ar.AddressID 
        }); 
     var resultsJoined = results 
         .GroupJoin(addresses, 
         ar => ar.AddressRelID, 
         a => a.AddressID, 
         (ar, a) => new 
         { 
          CustomerName = ar.CustomerName, 
          AddressLine = addresses.Select(b => b.StreetAddress).FirstOrDefault() 
         }); 
     foreach(var item in resultsJoined) 
     { 
      Console.WriteLine(item.CustomerName); 
      Console.WriteLine(item.AddressLine); 
      Console.WriteLine("-----------------"); 

     } 
    } 
} 

public class AddressRelation 
{ 
    public int AddressRelationID { get; set; } 
    public int CustomerID { get; set; } 
    public int AddressID { get; set; } 
    public AddressRelation(int id, int customerId, int addressId) 
    { 
     AddressRelationID = id; CustomerID = customerId; AddressID = addressId; 
    } 
    public static List<AddressRelation> GetAllAddressRelations() 
    { 
     var AllAddressRelations = new List<AddressRelation>();//simulate data returned from db 
     var addressRelation1 = new AddressRelation(1, 1, 1); 
     var addressRelation2 = new AddressRelation(2, 3, 3); 
     var addressRelation3 = new AddressRelation(3, 2, 2); 
     AllAddressRelations.Add(addressRelation1); 
     AllAddressRelations.Add(addressRelation2); 
     AllAddressRelations.Add(addressRelation3); 

     return AllAddressRelations; 
    } 
} 
public class Address 
{ 
    public int AddressID { get; set; } 
    public string StreetAddress { get; set; } 
    public Address(int id, string streetAddress) 
    { 
     AddressID = id; StreetAddress = streetAddress; 
    } 
    public static List<Address> GetAllAddresses() 
    { 
     var AllAddresses = new List<Address>(); 
     Address customer1Address = new Address(1, "Elm St"); 
     Address customer2Address = new Address(2, "Willow Way"); 
     Address customer3Address = new Address(3, "Linq Ln"); 
     AllAddresses.Add(customer1Address); 
     AllAddresses.Add(customer2Address); 
     AllAddresses.Add(customer3Address); 
     return AllAddresses; 
    } 
} 
public class Customer 
{ 
    public int CustomerID { get; set; } 
    public string FirstName { get; set; } 
    public string LastName { get; set; } 

    public Customer(int id,string firstName, string lastName) 
    { 
     CustomerID = id; FirstName = firstName; LastName = lastName; 
    } 
    public static List<Customer> GetAllCustomers() 
    { 
     var AllCustomers = new List<Customer>(); 
     var customer1 = new Customer(1, "James", "T"); 
     var customer2 = new Customer(2, "Donnie", "H"); 
     var customer3 = new Customer(3, "Sarah", "H"); 
     AllCustomers.Add(customer1); 
     AllCustomers.Add(customer2); 
     AllCustomers.Add(customer3); 
     return AllCustomers; 
    } 
} 

}地址

Answer 1

因为你已经告诉它它返回的第一个客户地址：

AddressLine = addresses.Select(b => b.AddressLine1).FirstOrDefault() 

这里，addresses是全部地址。我怀疑你只是想：

AddressLine = a.Select(b => b.AddressLine1).FirstOrDefault() 

Answer 2

该查询不是很有表现力。如果我要加入使用LinqToObjects三个列表，我应该这样做：

var query = 
    from c in customers 
    join xr in addressRelations on c.CustomerId equals xr.CustomerId 
    join a in addresses on xr.AddressId equals a.AddressId 
    select new {Customer = c, Address = a}; 

---

看起来像另一个错误。我敢打赌，AddressRelId是AddressRelation表的关键，而不是你想用来连接到Address表的地址。

.GroupJoin(addresses, 
ar => ar.Address**Rel**ID, 
a => a.AddressID, 

---

在回应评论：

var query = customers 
    .Join(addressRelations, 
    c => c.CustomerId, 
    xr => xr.CustomerId, 
    (c, xr) => new {c, xr}) 
    .Join(addresses, 
    x => x.xr.AddressId, 
    a => a.AddressId, 
    (x, a) => new {c = x.c, xr = x.xr, a = a}) 
    .Select(x => new {Customer = x.c, Address = x.a});