Bundle: Indexed Properties

Another bundle available in RavenDB is Indexed Properties bundle. It enables auto-updating of document properties by Indexing process, but what does it mean? In real-life scenario it gives user the ability to utilize index calculated values.

Lets consider a common case where we have a Customer and bunch of Orders and we want, without much of effort, to be able to get average order amount for that customer. We can do it in couple of ways, but one of them is particularly interesting.

public class Customer
{
	public string Id { get; set; }

	public string Name { get; set; }

	public decimal AverageOrderAmount { get; set; }
}

public class Order
{
	public string Id { get; set; }

	public string CustomerId { get; set; }

	public decimal TotalAmount { get; set; }
}

To use bundle, at the beginning we must activate it. It can be done server-wide or per database. To activate bundle during database creation process you need to add IndexedProperies to Raven/ActiveBundles setting.

store.DatabaseCommands.CreateDatabase(new DatabaseDocument
	{
		Id = "ExampleDB",
		Settings =
			{
				{ "Raven/ActiveBundles", "IndexedProperties" }
			}
	});

Second step is to create an index that will calculate the average.

public class OrderResults
{
	public string CustomerId { get; set; }

	public decimal TotalOfOrderAmounts { get; set; }

	public int CountOfOrders { get; set; }

	public decimal AverageOrderAmount { get; set; }
}

public class OrdersAverageAmount : AbstractIndexCreationTask<Order, OrderResults>
{
	public OrdersAverageAmount()
	{
		Map = orders => from order in orders
		                select new
			                {
				                CustomerId = order.CustomerId,
				                TotalOfOrderAmounts = order.TotalAmount,
				                CountOfOrders = 1,
				                AverageOrderAmount = 0
			                };

		Reduce = results => from result in results
		                    group result by result.CustomerId
		                    into g
		                    let total = g.Sum(x => x.TotalOfOrderAmounts)
		                    let count = g.Sum(x => x.CountOfOrders)
		                    select new
			                    {
				                    CustomerId = g.Key,
				                    TotalOfOrderAmounts = total,
				                    CountOfOrders = count,
				                    AverageOrderAmount = total / count
			                    };
	}
}

Next, we will have to create a document Raven/IndexedProperties/Index_Name that consists of document key property name (in our case CustomerId) and a mapping between index field names and our document properties.

var ordersAverageAmount = new OrdersAverageAmount();
ordersAverageAmount.Execute(store);

store.DatabaseCommands.Put("Raven/IndexedProperties/" + ordersAverageAmount.IndexName,
                           null,
                           RavenJObject.FromObject(new IndexedPropertiesSetupDoc
	                           {
		                           DocumentKey = "CustomerId",
		                           FieldNameMappings =
			                           {
				                           { "AverageOrderAmount", "AverageOrderAmount" }
			                           }
	                           }),
                           new RavenJObject());

After this, whenever we add new orders to our customers, the AverageOrderAmount property will be updated automatically.

using (var session = store.OpenSession())
{
	session.Store(new Customer { Id = "customers/1", Name = "Customer 1" });
	session.Store(new Customer { Id = "customers/2", Name = "Customer 2" });

	session.Store(new Order { Id = "orders/1", CustomerId = "customers/1", TotalAmount = 10 });
	session.Store(new Order { Id = "orders/2", CustomerId = "customers/1", TotalAmount = 5 });
	session.Store(new Order { Id = "orders/3", CustomerId = "customers/1", TotalAmount = 3 });

	session.Store(new Order { Id = "orders/4", CustomerId = "customers/2", TotalAmount = 1 });
	session.Store(new Order { Id = "orders/5", CustomerId = "customers/2", TotalAmount = 3 });

	session.SaveChanges();
}

using (var session = store.OpenSession())
{
	var customer1 = session.Load<Customer>("customers/1"); // AverageOrderAmount is 6
	var customer2 = session.Load<Customer>("customers/2"); // AverageOrderAmount is 1.5
}