Accessing an object using another object in Entity Framework

Question

I have three classes like this :

public class Cancellations
{
    public int ID {get; set;}
    public string CustomerID {get; set;}
    public string CustomerName {get; set;}
}

public class Service
{
    public int ID {get; set;}
    public string CustomerID2 {get; set;}
    public string ServiceName {get; set;}
}

public class Bill
{
    public int ID {get; set;}
    public string CustomerID3 {get; set;}
    public string City {get; set;}
}

There is such a relation in these databases : Service.ID=Cancellations.CustomerID and Bill.CustomerID3 = Service.CustomerID2 . What I'm trying to achieve is that how can I get the correct city when I have CustomerID in Cancellations object. Can you give me tips about that? Thanks.

Answer 1

Suppose you have the CustomerID then:

With C# and Linq

using System.Linq;

--

// Suppose this is your cancellation object's CustomerID
int _customerID = 123;

--

var resultObj = from billObj in Bills 
            join serviceObj in Service on Service.CustomerID2 equals billObj.CustomerID3
            join cancellationObj in Cancellation on Cancellation.CustomerID equals serviceObj.ID
            where CancellationObj.CustomerID == _customerID
            select new { Bills = billObj };

--

String City = resultObj.Select(x => x.City).FirstOrDefault();

I would suggest you give your objects more meaningful names if possible.

Answer 2

Just a straight forward join:

var result = (from c in db.Cancellations
              join s in db.Service on c.CustomerID equals s.ID
              join b in db.Bill on s.CustomerID2 equals b.CustomerID3 
              select new { c.Id, c.CustomerName, b.City }).ToList();

2 recommendations:

1. Rename your properties/classes - it feels they make little sense
2. Look up Navigation Propertires