How does EF4 compare with NHibernate?

Question

Is it any better? I heard the CodeFirst extension but is it ready for primetime. Please share your experience with development, any performance overheads, etc.

Answer 1

I think this is a timely question, as I was wondering the exact same thing. I am trying to create a serious e-commerce model and I am trying to keep my POCOs free of persistence concerns as well as trying to stay true to Domain Driven Design. So far, I am very wary, and I am on the fence about whether I should jump ship to NHibernate. The only thing keeping me from doing so is that I assume that Microsoft will improve (and quickly).

Some of the biggest problems so far:

• Inability to finely control object materialization. EF calls the zero-arg constructor on your POCO, and this is a behavior you cannot change.
• No enum support. The community has been screaming -- screaming! -- for this, and it hasn't happened. The workarounds are terrible, and pollute your domain model.
• Weird mapping bugs when trying to control column names and relationships in the database. The main ones I can think of are with compound keys and many-to-many relationships. These can be worked around, and I assume these will be fixed by release time, but they are frustrating nonetheless.
• Bad SQL. I also do DBA work, and the SQL that EF generates (with or without Code-First) is atrocious.

And this is just the tip of the iceberg: I am only starting to learn EF4 and I'm running into awful roadblocks. As I think of more reasons, I'll add them here. I'm still struggling through it.

(I wonder whether the community will give it another vote of "no confidence.")

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More:

• To add to the "Weird mapping bugs" problem: You cannot control the name of a column if it participates in a self-referencing relationship (for example, if you have a hierarchy). I assume this will be fixed in the final release.
• Lack of batching, resulting in multiple roundtrips to the database. For example, how do you delete a bunch of items from a collection? Load all entities into memory and delete them one at a time. A smaller gripe is the number of DB hits when inserting into tables that participate in an inheritance relationship.
• No intelligent way to deal with model changes. EF Code-First loves to completely drop your entire database if it needs to change the schema.
• Few extensibility points. You can literally count on one hand the number of events that EF4 allows you to subscribe to (and Code-First doesn't provide much more).

Answer 2

As for me - I prefer EF but with some enhancements. Basically EF offers to you the following advantages:

• Visual Model Editor
• Database/Model Update wizard (instead of manual XML changes - what is terrible for me)

Also, I'm using 3-rd party commercial tools based on EF and L2S (LinqConnect) that provide for me the following features:

• Geography support
• Optimized SQL generation
• Product absolutely integrated to Visual Studio
• Smart database update wizard (synchronization mode)