Fetching POCO Entities and Value Objects using Linq To SQL​

I have been trying to practice domain driven design for the last few years.
During this time, I have learnt that there are almost as many ways to implement DDD as there are practitioners.

For the last month I have been spending my spare time porting the awesome Java framework QI4J to .NET.
QI4J is the brain child of Rickard Öberg and Niclas Hedhman and it attempts to enable Composite Oriented Programming for the Java platform.
(For more info regarding Composite Oriented Programming see the QI4J website: http://www.qi4j.org/ )

When dealing with a fat domain model, there is often a need to be able to inject different services into your entities.
e.g. you might want to inject some domain service like “ITaxCalcualtorService” or an infrastructure service like “IEmailNotificationService” into your entities.

This is a short rant..

When Linq To Sql was released we were told that it did support eager loading.
Which was a bit misleading, it did allow us to fetch the data we wanted upfront, but it did so by issuing one database query per object in the result set.
That is, one query per collection per object, which is a complete performance nightmare. (Ripple loading)

[EDIT]
I was wrong!

I downloaded the VS 2010 beta1 today and started to dissect Entity Framework 4.

Ok, the title is not quire accurate, I’m not aware of any way to accomplish truly immutable types for Entity Framework.

Here is a little trick if you want to issue a query to the database and select a batch of entities by ID only: