using System;

using System.Collections.Generic;

using System.Text.RegularExpressions;

using System.Linq;

public class Program

{

    public class Component

    {

        public string Type {get; set;}

        public List<ComponentDetails> Details {get; set;}

    }

    public class ComponentDetails

    {

        public string Filename {get; set;}

        public string Size {get; set;}

        public DateTime Date {get; set;}

    }

    public static void Main()

    {

        var source = new List<Component>()

        {

            new Component()

            {

                Type = "foo"

            },

            new Component()

            {

                Type = "bar"

            },

            new Component()

            {

                Type = "tra"

            }

        };

        var destination =  new List<Component>()

        {

            new Component()

            {

                Type = "foo",

                Details = new List<ComponentDetails>()

                {

                    new ComponentDetails() { Filename = "foo.txt" }

                }

            },

            new Component()

            {

                Type = "bar",

                Details = new List<ComponentDetails>()

                {

                    new ComponentDetails() { Filename = "bar.txt" }

                }

            },

            new Component()

            {

                Type = "la",

                Details = new List<ComponentDetails>()

                {

                    new ComponentDetails() { Filename = "la.txt" }

                }

            }

        };

        var matched = from s in source

            join d in destination on s.Type equals d.Type into tmp

            from t in tmp.DefaultIfEmpty()

            select new { s, d = t };

        System.Console.WriteLine(matched.Count());

        foreach (var i in matched) {

            System.Console.WriteLine(i.s.Type);

            System.Console.WriteLine(i.d != null ? i.d.Details[0].Filename : string.Empty);

        }

​

    }

}