What’s the difference between LINQ to SQL and Entity Framework?

The first big difference between the Entity Framework and LINQ to SQL is that the EF has a full provider model which means that as providers come online (and there are several in beta now and many which have committed to release within 3 months of the EF RTM), you will be able to use the EF against not only SQL Server and SQL CE but also Oracle, DB2, Informix, MySQL, Postgres, etc.

Next there is the fact that LINQ to SQL provides very limited mapping capabilities.  For the most part L2S classes must be one-to-one with the database (with the exception of one form of inheritance where there is a single table for all of the entity types in a hierarchy and a discriminator column which indicates which type a particular row represents).  In the case of the EF, there is a client-side view engine which can transform queries and updates made to the conceptual model into equivalent operations against the database.  The mapping system will produce those views for a variety of transformations.

You can apply a variety of inheritance strategies: Assume you have an inheritance model with animal, dog:animal & cat:animal.  You can not only do what L2S does and create a single table with all the properties from animal, dog & cat plus a column that indicates if a particular row is just a generic animal or a dog or a cat, but you can also have 3 tables where each table has all of the properties of that particular type (the dog table has not only dog-specific columns but also all the same columns as animal), or 3 tables such that the dog and cat tables have only the key plus those properties specific to their type of animal and retrieving a dog object would involve a join between the animal table and the dog table.  And you can further combine these strategies so some parts of a hierarchy might live in one table and some parts in separate tables.

In addition you can do what we call “entity splitting” where a single type has properties which are drawn from two separate tables, and you can model complex types where there is a type which is nested within a larger entity and which doesn’t have its own separate identity–it just groups some properties together.  The best example of this is something like address where the street, city, state and zip properties go together logically, but they don’t have independent identity.  The address is only interesting as a set of properties that are part of a customer or whatever.  As you have noticed, for v1 you can’t create complex types with the designer in the EF–you have to code them by hand in the XML files.

Make it simple:

• LINQ to SQL is good for rapid development with SQL Server. EF is for enterprise scenarios and works with SQL Server as well as other databases.
• LINQ maps directly to tables. One LINQ entity class maps to one table. EF has a conceptual model and that conceptual model maps to the storage model via mappings. So one EF class can map to multiple tables, or one table can map to multiple classes.
• LINQ is more targeted towards rapid development while EF is for enterprise level where the need is to develop a loosely coupled framework.