What is Entity Framework fluent api?

Entity Framework 4.1 introduces the code first approach of writing database models. This is also called POCO (Plain Old CLR Objects). The idea is that you can build your database from these classes, rather then building the database first and creating a model from that.

There are tons of good blog articles and MSDN documentation on this. A good place to start would be

http://blogs.msdn.com/b/adonet/archive/2010/12/14/ef-feature-ctp5-fluent-api-samples.aspx

http://weblogs.asp.net/scottgu/archive/2010/12/08/announcing-entity-framework-code-first-ctp5-release.aspx

http://weblogs.asp.net/manavi/archive/2011/03/27/associations-in-ef-4-1-code-first-part-1-introduction-and-basic-concepts.aspx

Regards the fluent API, this is basically using the EF classes to build your database e.g.:

modelBuilder.Entity<Category>().HasKey(c => c.CategoryCode);

So you're manually stating that the Category table has a primary key named `CategoryCode'. You can also declare the PK like this:

public class Category
{
    [Key]    
    public int CategoryCode { get; set;}
}

The [Key] attribute comes from Data Annotations

POCO stands for Plain Old CLR Object.

Article on Fluent API.

You can also check the Code First Fluent API section on MSDN here http://msdn.microsoft.com/en-us/library/hh295844