What exactly does the EF wizard update when doing "Update model from database" in VS 2010?

Question

Using VS2010 and .NET 4 what exactly does the ADO.NET EF wizard update when you right click in the EF model and select Update from database because I have a feeling that very little.

For instance, making a column optional (null values allowed) in SQL Server Management (a value that was previously not nullable) and updating the model in VS, does not change that entity property to Nullable = true. It remains false. That's just one example but I think there's more, like column lengths changes etc.

Answer 1

The .edmx file that is your Entity Framework model is actually an XML-based file that contains (primarily) three separate sections:

1. A "storage model" that contains data about the database itself.
2. A "conceptual model" that defines the entities in your application.
3. A mapping between #1 and #2.

Empirically, I have determined that the 'update from database' process will add, remove, or modify anything in the storage model that appears to be inconsistent with the current database schema. On the other hand, it will not modify or remove anything in the conceptual model (it will add stuff, though).

This makes sense because there is not necessarily a 1-1 correspondence between entities (and their properties) in your application and tables (and their fields) in the database.