using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var itemsNotaFiscal = new List<ItemNotaFiscal>

        {

            new ItemNotaFiscal(123, 1, 10.0m),

            new ItemNotaFiscal(123, 2, 20.0m),

            new ItemNotaFiscal(123, 3, 30.0m),

            new ItemNotaFiscal(222, 1, 10.0m),

            new ItemNotaFiscal(222, 2, 20.0m),

            new ItemNotaFiscal(444, 1, 10.0m),

            new ItemNotaFiscal(444, 2, 20.0m)

        };

        //var query = 

        //from i1 in itemsNotaFiscal

        //join i2 in itemsNotaFiscal

        //on i1.NotaFiscalId equals i2.NotaFiscalId

        //select i1;        

​

    var query =

        itemsNotaFiscal.AsEnumerable().Join(itemsNotaFiscal.AsEnumerable(),

        i1 => i1.NotaFiscalId,

        i2 => i2.NotaFiscalId,

        (i2, i1) => i1);    

​

        foreach (var item in query)

        {

            Console.WriteLine($"NotaFiscalId: {item.NotaFiscalId}, ProdutoId: {item.ProdutoId}, Valor: {item.Valor:C}");

        }

    }

}

​

public class ItemNotaFiscal

{

    public ItemNotaFiscal(int notaFiscalId, int produtoId, decimal valor)

    {

        NotaFiscalId = notaFiscalId;

        ProdutoId = produtoId;

        Valor = valor;

    }

​

    public int NotaFiscalId { get; set; }

    public int ProdutoId { get; set; }

    public decimal Valor { get; set; }

}