I’ve now used and/or tried LINQ to SQL, Entity Framework, and Fluent NHibernate and can now say I understand the differences as expressed in the ADO.NET Entity Framework Vote of No Confidence. Yet I still appreciate what the former two products from Microsoft offer. Well, I like LINQ to SQL anyway. After spending four hours today trying to create a simple example with Entity Framework and getting nowhere with many-to-many mappings despite several blogs’ assistance, I finally gave up. I think the problem with LINQ to SQL and Entity Framework is not in their usefulness but in the approach Microsoft has tried to take in marketing them as object-relational mapping technologies.
An object-relational mapping technology generally takes an object and maps it to a database, not the other way around. At least, I think that’s how it started. The abundance of MVC frameworks using the Active Record pattern seems to have changed that recently with generators creating models from database tables, though many of these actually create the tables in the database from the object definition, as well. Nevertheless, I’d disagree with Microsoft that LINQ to SQL and Entity Framework qualify as ORM technologies, though they do perform that role, as well.
LINQ to SQL and Entity Framework provide a language-integrated object database against which to create applications. This is huge! Let that sink in a bit. Now, I find nothing wrong with that approach. In fact, it’s quite nice! The trouble is that developers think, “Wow, I’ve got all these great objects ready to use!” Not so fast. You have entities that represent rows in tables, not business objects. Yes, LINQ to SQL and Entity Framework provide means of modifying those classes to mimic more class-like behavior (and that can indeed be a great benefit do easing domain model or active record development) but really should not be used for anything other than database records.
This greatly simplifies any data mapping you have to do between your domain objects and your database, and you can write everything in your OO language of choice. If you want something more automatic, you might try an object-to-object mapper (e.g. NBear–though I haven’t tried it myself and can’t imagine that object-to-object mapping would be that difficult).
As a final analysis, in case you care, I really like LINQ to SQL’s defaults. It’s super simple to get started and use, though it’s only for SQL Server. Entity Framework… I am just not a fan. If I can stay away, I will. Maybe someone will show me how to configure it so that it works for me, but so far it’s a FAIL. Also, keep tabs on DbLinq. It’s an open source tool that attempts to mimic LINQ to SQL for SQL Server and a number of other database technologies and should work on Mono. Of course, NHibernate is great for those who would rather connect to a real database, and I found Fluent NHibernate to be a great tool. I love its fluent interface for mapping to the database and its AutoMapping functionality. However, making everything virtual annoyed me and really makes me question how so many can prefer it for persistence ignorance when it so obviously requires that detail. (I get it’s a small sacrifice, but I wouldn’t code that way normally, so I am quite reminded that I’m connecting to a database through NHibernate.)