Entity Framework 4.0: Optimal and horrible SQL

Lately I had Entity Framework 4.0 session where I introduced new features of Entity Framework. During session I found out with audience how Entity Framework 4.0 can generate optimized SQL. After session I also showed guys one horrible example about how awful SQL can be generated by Entity Framework. In this posting I will cover both examples.

Optimal SQL

Before going to code take a look at following model. There is class called Event and I will use this class in my query.

Here is the LINQ To Entities query that uses small anonymous type.

var query = from e in _context.Events
        select new { Id = e.Id, Title = e.Title };
Debug.WriteLine(((ObjectQuery)query).ToTraceString());

Running this code gives us the following SQL.

SELECT  

    [Extent1].[event_id] AS [event_id],  

    [Extent1].[title] AS [title]  

FROM [dbo].[events] AS [Extent1]

This is really small – no additional fields in SELECT clause. Nice, isn’t it?

Horrible SQL

Ayende Rahien blog shows us darker side of Entiry Framework 4.0 queries. You can find comparison betwenn NHibernate, LINQ To SQL and LINQ To Entities from posting What happens behind the scenes: NHibernate, Linq to SQL, Entity Framework scenario analysis. In this posting I will show you the resulting query and let you think how much better it can be done.

Well, it is not something we want to see running in our servers. I hope that EF team improves generated SQL to acceptable level before Visual Studio 2010 is released.

There is also morale of this example: you should always check out the queries that O/R-mapper generates. Behind the curtains it may silently generate queries that perform badly and in this case you need to optimize you data querying strategy.

Conclusion

Entity Framework 4.0 is new product with a lot of new features and it is clear that not everything is 100% super in its first release. But it still great step forward and I hope that on 12.04.2010 we have new promising O/R-mapper available to use in our projects.