public class OrderItem
    {
        public int OrderItemID { get; set; }
        public int Quantity { get; set; }
        public string ItemCode { get; set; }
        public string Description { get; set; }
    }

    public class Order
    {
        public Order()
        {
            Items = new List<OrderItem>();
        }
        public int OrderID { get; set; }        
        public string Description { get; set; }         
        public decimal TotalWeight { get; set; }         
        public string ShippingMethod { get; set; }
        public List<OrderItem> Items { get; set; } 
    }

OrderInfo.ShippingMethod

TotalAmount + (OrderInfo.TotalWeight * 0.50m) 

static void Main(string[] args)
        {
            Order myOrder = new Order
            {
                OrderID = 1,
                Description = "Need some stuff",
                ShippingMethod = "2ndDay",
                TotalWeight = 100
            };
            IDictionary<String, object> input = new Dictionary<String, Object>
            {
                { "OrderInfo",myOrder}
            };
            IDictionary<String, Object> output = WorkflowInvoker.Invoke(new OrderWF(), input);
            Decimal total = (Decimal)output["TotalAmount"];
            Console.WriteLine("Workflow returned ${0} for my order total", total);
            Console.WriteLine("Press ENTER to exit"); 
            Console.ReadLine();

            //Activity workflow1 = new OrderWF();
            //WorkflowInvoker.Invoke(workflow1);
        }

LINQ to Entities does not recognize the method 'System.String

• Introduction to LINQ
• C# 3.0 Language Features
• LINQ to Objects
• Lambda Expressions
• LINQ to DataSets
• Getting Started with LINQ to SQL
• Additional LINQ to SQL Features
• LINQ to XML
• LINQ to Entities and the Entity Framework

IEnumerable input = new object[] { "Apple", 33, "Sugar", 44, 'a', new DateTime()};
IEnumerable<string> query = input.OfType<string>();
foreach (var item in query)
{
   Console.WriteLine(item);
}

 class Ingredient
  {
     public string Name { get; set; }
  }
  class DryIngredient : Ingredient
  {
     public int Grams { get; set; }
  }

  class WetIngredient : Ingredient
  {
     public int Millilitres { get; set; }
  }

IEnumerable<Ingredient> input = new Ingredient[]
{
   new DryIngredient { Name = "Flour" },
   new WetIngredient { Name = "Milk" },
   new WetIngredient { Name = "Water" }
};

IEnumerable<WetIngredient> query = input.OfType<WetIngredient>();
foreach (WetIngredient item in query)
{
   Console.WriteLine(item.Name);
}

IEnumerable input = new object[]
{
   "Apple", 33, "Sugar", 44, 'a', new DateTime()
};

IEnumerable<string> query = input.Cast<string>();
foreach (string item in query)
{
   Console.WriteLine(item);
}

IEnumerable input = new object[]{ "Apple", "Sugar", "Flour" };
IEnumerable<string> query =
from string i in input
select i;

foreach (var item in query)
{
   Console.WriteLine(item);
}

class Recipe
{
   public int Id { get; set; }
   public string Name { get; set; }
   public int Rating { get; set; }
}

IEnumerable<Recipe> recipes = new[]
{
   new Recipe { Id = 1, Name = "Apple Pie", Rating = 5 },
   new Recipe { Id = 2, Name = "Cherry Pie", Rating = 2 },
   new Recipe { Id = 3, Name = "Beef Pie", Rating = 3 }
};

Dictionary<int, Recipe> dict = recipes.ToDictionary(x => x.Id);
foreach (KeyValuePair<int, Recipe> item in dict)
{
   Console.WriteLine($"Key={item.Key}, Recipe={item.Value}");
}

class Recipe
{
   public int Id { get; set; }
   public string Name { get; set; }
   public byte Rating { get; set; }
}

IEnumerable<Recipe> recipes = new[]
{
   new Recipe { Id = 1, Name = "Apple Pie", Rating = 5 },
   new Recipe { Id = 1, Name = "Banana Pie", Rating = 5 },
   new Recipe { Id = 2, Name = "Cherry Pie", Rating = 2 },
   new Recipe { Id = 3, Name = "Beef Pie", Rating = 3 }
};

ILookup<byte, Recipe> look = recipes.ToLookup(x => x.Rating);
foreach (IGrouping<byte, Recipe> ratingGroup in look)
{
   byte rating = ratingGroup.Key;
   Console.WriteLine($"Rating {rating}");
   foreach (var recipe in ratingGroup)
   {
      Console.WriteLine($" - {recipe.Name}");
   }
}

Ingredient[] ingredients =
{
   new Ingredient {Name = "Sugar", Calories = 500},
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 150},
   new Ingredient {Name = "Flour", Calories = 50},
   new Ingredient {Name = "Butter", Calories = 500}
};

Ingredient element = ingredients.First();
Console.WriteLine(element.Name);

Ingredient[] ingredients =
{
   new Ingredient {Name = "Sugar", Calories = 500},
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 150},
   new Ingredient {Name = "Flour", Calories = 50},
   new Ingredient {Name = "Butter", Calories = 500}
};

Ingredient element = ingredients.First(x=>x.Calories==150);
Console.WriteLine(element.Name);

 Ingredient[] ingredients =
{
   new Ingredient {Name = "Sugar", Calories = 500},
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 150},
   new Ingredient {Name = "Flour", Calories = 50},
   new Ingredient {Name = "Butter", Calories = 500}
};
Ingredient element = ingredients.First(x=>x.Calories==1500);

Ingredient[] ingredients =
{
   new Ingredient {Name = "Sugar", Calories = 500},
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 150},
   new Ingredient {Name = "Flour", Calories = 50},
   new Ingredient {Name = "Butter", Calories = 500}
};

Ingredient element = ingredients.FirstOrDefault(x=>x.Calories==1500);
Console.WriteLine(element==null);

Ingredient[] ingredients =
{
   new Ingredient {Name = "Sugar", Calories = 500},
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 150},
   new Ingredient {Name = "Flour", Calories = 50},
   new Ingredient {Name = "Butter", Calories = 500}
};
Ingredient element = ingredients.Last(x=>x.Calories==500);
Console.WriteLine(element.Name);

Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 }
};

Ingredient element = ingredients.Single();
Console.WriteLine(element.Name);

Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 },
   new Ingredient {Name = "Butter", Calories = 150},
   new Ingredient {Name = "Milk", Calories = 500}
};
Ingredient element = ingredients.Single(x => x.Calories == 150);
Console.WriteLine(element.Name);

 Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 },
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 50}
};
Ingredient element = ingredients.SingleOrDefault(x => x.Calories == 9999);
Console.WriteLine(element==null);

 Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 },
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 50}
};

Ingredient element = ingredients.ElementAt(2);
Console.WriteLine(element.Name);

Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 },
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 50}
};
Ingredient element = ingredients.ElementAtOrDefault(5);
Console.WriteLine(element==null);

Ingredient[] ingredients =
{
   new Ingredient { Name = "Sugar", Calories = 500 },
   new Ingredient {Name = "Egg", Calories = 100},
   new Ingredient {Name = "Milk", Calories = 50}
};

IEnumerable<Ingredient> query = ingredients.DefaultIfEmpty();
foreach (Ingredient item in query)
{
  Console.WriteLine(item.Name);
}

Ingredient[] ingredients = { };
IEnumerable<Ingredient> query = ingredients.DefaultIfEmpty();
foreach (Ingredient item in query)
{
   Console.WriteLine(item == null);
}