Complex Linq query is not working as expected

Question

I want to combine results from 4 tables and select specific fields using LINQ. Please bear with me since I have not done complex LINQ queries.

Table 1 - Subscriber<

Answer 1

It's not really LINQ that's tripping up here, it's LINQ to Entities. Are you using Entity Framework? Does your model have the relationships defined in it? If you have foreign keys in your database, and build your model in Entity Framework with database first, it will map all the entity relationships for you.

If yes, you can then do something like:

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

public class Program
{
    public class Subscriber{
        public string Name {get;set;}
        public List Subscriptions{get;set;}
    }

    public class Subscription{
        public string Name {get;set;}
    }

    public class MyViewModelItem{
        public string SubscriberName{get;set;}
        public string SubscriptionNames {get;set;}
    }

    public static void Main()
    {
        Console.WriteLine("Hello World");

        // create some dummy data
        var data = new List{
            new Subscriber{
                Name = "Arnold",
                Subscriptions = new List(){
                    new Subscription{
                        Name = "Subscription A"
                    },
                    new Subscription{
                        Name = "Subscription B"
                    },
                    new Subscription{
                        Name = "Subscription C"
                    }
                }
            },
            new Subscriber{
                Name = "Betty",
                    Subscriptions = new List()
            },
            new Subscriber{
                Name = "Christopher",
                Subscriptions = new List(){
                    new Subscription{
                        Name = "Subscription A"
                    }
                }
            }
        };

        // here's the query and it becomes much simpler
        var myViewModel = data
            .Select(i=> new MyViewModelItem{
                SubscriberName = i.Name,
                SubscriptionNames = string.Join(", ", i.Subscriptions.Select(j=>j.Name))
            })
            .ToList();

        // this shows the output
        foreach(var item in myViewModel){
            Console.WriteLine(string.Format("subscriber: {0}, subscriptions: {1}",item.SubscriberName,item.SubscriptionNames));
        }

    }
}

Output:

Hello World subscriber: Arnold, subscriptions: Subscription A, Subscription B, Subscription C subscriber: Betty, subscriptions: subscriber: Christopher, subscriptions: Subscription A