Unless you have been living under a rock, you should already know about the controversy over the nHibernate mafia's Microsoft Entity Framework's Vote of No Confidence. The manifesto says that the upcoming Entity Framework (to be released soon via .NET 3.5 SP1) is just not usable. As far as ORMs go, there are some valid points working against EF- in order of (my) importance:
The manifesto also brings up some Domain Driven Design issues that I feel are less important than the above four bullets. To their credit the normally reserved EF team has responded quickly and nicely to the manifesto. On the heels of last week's transparent-design process announcement, Tim Mallalieu gave a detailed reply which has started a good discussion and wiki. They are listening and that is good. Since the Entity Framework is starting work this week on v.next, they have also put together an advisory council including Eric Evans, Martin Fowler, Paul Hruby, Jimmy Nilsson, and myself.
To some degree the vote of no confidence worked, they got Tim's attention. I think that the manifesto has some very valid points, but I also think it lacks professionalism. Anyone can say something sucks, it is more important to give valid feedback, suggest solutions, and engage in a dialog. (The vote of no confidence was just too in your face-and a dialog was stated only because of the professionalism of the EF team.) In addition there are some mafia style attacks on anyone who does not agree with them, most recently against the always honest and open Julie Lerman.
So this blog post sounds like an endorsement of the Entity Framework and ORMs in general, right?
My first problem with ORMs in general is that they force you into a "objects first" box. Design your application and then click a button and magically all the data modeling and data access code will work itself out. This is wrong because it makes you very application centric and a lot of times a database model is going to support far more than your application. In addition an SOA environment will also conflict with ORM.
I prefer to build the application's object model and the data model at about the same time, with a "whiteboarding" approach that outlines the flows of data and functionality across the business process and problem set. Maybe it is the MBA talking but I tend to be "business and customers first" when I design a system. (Those of you that know me know that I have designed some very large and scalable systems in my day.) I usually like to "follow the money" as Ron Rose of Priceline taught me 10 years ago. In addition, I prefer a very agile design process where you are constantly making changes to your design in the early sprints, the database and object model are both part of this process.
My second major problem with ORMs is that ORMs are a solution to a problem that should not be solved. Developers who write object oriented and procedural code like C# and Java have trouble learning the set-based mathematics theory that govern the SQL language. Developers are just plain old lazy and don't want to code SQL since it is too "hard." That is why you see bad T-SQL: developers try to solve it their way, not in a set-based way.
The premise of EF, LINQ, nHibernate, and Luca Bolongese’s original premise with ObjectSpaces, is that set-based theory causes an “impedance mismatch” between data access and all the other (more procedural) coding we do. And it’s ORMs to the rescue to resolve the impedance mismatch.
So ORMs are trying to solve the issue of data access in a way that C# and VB developers can understand: objects, procedural, etc. That is why they are doomed to fail. The further you abstract the developer from thinking in a set-based way and have them write in a procedural way and have the computer (ORM) convert it to a set-based way, the worse we will be off over time.
What I am saying (and have been saying for a long time) is that we should accept, no, embrace the impedance mismatch! While others are saying we should eradicate it, I say embrace it.
ORM tools should evolve to get closer to the database, not further away.
One of the biggest hassles I see with LINQ to SQL is the typical many-to-many problem. If I have a table of Ocean Liners, vessels, and ports, I’ll typically have a relational linking table to connect the vessels and ports via a sailing. (Can you tell I am working with Ocean Freight at the moment?) The last thing I want at the object layer is three tables! (And then another table to look up the Ocean Liner that operates the vessel.) Unfortunately, this is what most tools give me. Actually I don't even want one table, I want to hook object functionality to underlying stored procedures. I really want a port object with a vessel collection that also contains the ocean liner information. At least the Entity Framework does this however I have major concerns about the performance of the code it produces.
The ironic thing I’m now seeing is developers who are lazy and don't want to learn SQL using tools that will produce SQL for them. The SQL is bad, and now those same anti-SQL lazy developers are struggling to read pages of generated and near-unreadable SQL trying to solve performance problems. They’re dealing with SQL that’s more verbose and orders of magnitude harder to understand than what was needed in the first place!
So where do we go from here? We can't just keep pretending that this mismatch problem can be solved and keep throwing good money after bad. As Ted Neward said that is the Vietnam of Computer Science.
I say that developers should start embracing the impedance mismatch. I also say that Microsoft and other ORM vendors need to realize that embracing the mismatch is a good thing and design ORM tools that allow this. (This is the advice I will give at the EF council.) I am not anti-ORM (even tho I did trash LINQ on stage at TechEd last year), but I am pro using the right tool/technology for the right job. ORM is real good for CRUD and real bad at other things. Let's start from there. To quote Ted, "Developers [should] simply accept that there is no way to efficiently and easily close the loop on the O/R mismatch, and use an O/R-M to solve 80% (or 50% or 95%, or whatever percentage seems appropriate) of the problem and make use of SQL and relational-based access (such as "raw" JDBC or ADO.NET) to carry them past those areas where an O/R-M would create problems."
Hopefully "cooler heads will prevail."
My fellow RD Greg Low brought to my attention that my discussion on Linq to SQL above is very similar to an email he sent not to long ago. At Triton Works (the ocean containers) we used his example in our own entity model debate and I realized after he pointed it out to me that the words above are just too close to his, so I am giving him the credit above. (Though he did not call programmers lazy and anti-SQL, I did.)
FYI, we went with POAN or Plain Old ADO.NET, ocean containers are old school.
The inspiration for this post came from not only the public debate on the EF vote of no confidence but also a private email discussion on nHybernate, EF and Linq to SQL between: Greg, Andrew Brust, Rocky Lhotka, Sten Sundbland, Joel Semeniuk, Barry Gervin, and myself. I won't tell you who was on what side. If you want to know, you will have to ask them. Hint, hint, Canadians are lazy and anti-SQL. :)
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The opinions expressed herein are my own personal opinions and do not represent
my employer's view in anyway.