Loading Entities and Navigation Properties - Entity Framework 6 Recipes - page 133

Console.WriteLine("\nCustomers by Type");
Console.WriteLine("=================");
foreach (var customerType in customerTypes)
{
Console.WriteLine("Customer type: {0}", customerType.Description);
foreach (var customer in customerType.Customers)
{
Console.WriteLine("{0}", customer.Name);
foreach (var email in customer.CustomerEmails)
{
Console.WriteLine("\t{0}", email.Email);
}
}
}
}
The output of the code in Listing 5-2 is the following:
Customers
=========
Joan Smith is a Web Customer, email address(es)
[e-mail]
[e-mail]
Bill Meyers is a Retail Customer, email address(es)
[e-mail]
Customers by Type
=================
Customer type: Web Customer
Joan Smith
[e-mail]
[e-mail]
Customer type: Retail Customer
Bill Meyers
[e-mail]
How It Works
By default, Entity Framework loads only entities that you specifically request. This is known as lazy loading and can
be quite efficient in the use case where a user is browsing your application and may navigate to different views based
upon his or her needs.
An alternative, loading the parent and related entities (keep in mind that our object graph is a set of parent/child
entities based on relationships, similar to parent/child database tables with foreign key relationships) at once, is known
as eager loading. This approach can be efficient when you know, up front, that you will require a large set of related
data, as it can retrieve all data (both from the parent and related entities) in a single query.
In Listing 5-2, to fetch the object graph all at once, we use the Include() method twice. In the first use, we start
the object graph with Customer and include an entity reference to the CustomerType entity. This is on the one side
of the one-to-many association. Then, in the subsequent Include() method (contained in the same line of code,
chained together), we get the many side of the one-to-many association, bringing along all of the instances of the