When to use LINQ-to-SQL versus Entity Framework?

Here's the latest comment I have found from Microsoft regarding Linq2Sql and EF...
http://msdn.microsoft.com/en-us/data/bb525059.aspx

Don't forget that there exist solutions outside of Microsoft as well (which has its pros and cons).
Some popular ORMs out there...

NHibernate, http://nhforge.org/
Subsonic, http://subsonicproject.com/
LightSpeed, http://www.mindscape.co.nz/products/lightspeed/
LLBLGEN, http://www.llblgen.com/defaultgeneric.aspx

Some of the above are commercial others OSS. NHibernate is a popular and mature ORM with origins from Java's Hibernate. There is a comparison between EF4 and NHibernate here. Note that the comparison might be a bit biased, since Oren is a contributor to NHibernate. Nevertheless it is a good read.

Good Luck!

Personallly I would use EF.  EF is a true OR/M where Linq 2 Sql is mostly a SQL obfuscator. With EF you can save/load and manage your objects where with Linq2Sql you still need to know the sql and data structure but you are pretending you don't.

On BASTA! Spring 2010, a presenter said the following:

"Don't choose Linq2Sql if you are starting a new project, the team that developed it, doesn't exist anymore. Choose EF 4.0. This is the way to go. Linq2Sql was merely one possible way which we decided to not follow anymore."

I wouldn't quite go that far.  The links above are outdated.  Microsoft has made some updates to Linq2SQL in .NET 4.0

http://damieng.com/blog/2009/06/01/linq-to-sql-changes-in-net-40

http://blog.linqexchange.com/index.php/linq-to-sql-changes-in-net-4-0/

I have not used any of them, but just wanted you to give a heads up if you start using Linq2Sql. It seems as the future for Linq2Sql is very uncertain, and Microsoft might make it obsolete in favor for EF. Something for you to consider when deciding upon which technology to use.


Reference:

Update on LINQ to SQL and LINQ to Entities Roadmap
http://blogs.msdn.com/b/adonet/archive/2008/10/29/update-on-linq-to-sql-and-linq-to-entities-roadmap.aspx

Microsoft kills Linq to SQL
http://ayende.com/Blog/archive/2008/10/31/microsoft-kills-linq-to-sql.aspx

The primary difference between the two frameworks is how they handle your models.  That should be clear enough.  ;^)  Just kidding, partly. 

The basic rule of thumb for which framework to use is how to plan on editing your data in your presentation layer. 

• Linq-To-Sql - use this framework if you plan on editing a one-to-one relationship of your data in your presentation layer.  Meaning you don't plan on combining data from more than one table in any one view or page.
• Entity Framework - use this framework if you plan on combining data from more than one table in your view or page.

To make this clearer, the above terms are specific to data that will be manipulated in your view or page, not just displayed.  This is important to understand.

With the Entity Framework you are able to "merge" tabled data together to present to the presentation layer in an editable form, and then when that form is submitted, EF will know how to update ALL the data from the various tables.

There are probably more accurate reasons to choose EF over L2S, but this would probably be the easiest one to understand.  L2S does not have the capability to merge data for view presentation.

I hope this answers your question.

King Wilder