Entity Framework: how to return a base type from L2E

Question

Considering the following architecture:

• a base object 'Entity'
• a derived object 'Entry:Base'
• and a further derived object 'CancelledEntry:Entry'

In EntitySQL I can write the following:

[...] where it is of (only MyEntities.Entry) [...]

to return only objects of type Entry and no Entity or CancelledEntry.

In linq to sql, the following command will return objects of type Entry and CancelledEntry.

EntityContext.EntitySet.OfType<Entry>()

What is the syntax/function to use to return only objects of type Entry?

Answer 1

Ok, I have found a partial solution:

EntityContext.EntitySet.OfType<Entry>().Where( obj => !(obj is CancelledEntry) )

This is quite awful however, since if I create a new derived object, I have to go in all the queries and specifically add a condition to remove it.

There has to be a better solution

Answer 2

Why don't you apply an extension method on IQueryable< Entry > called ApplyBaseEntryFilter() which would apply this filter and return an IQueryable< Entry >.

This is an example of how to reuse linq query fragments. Using extension methods on IQueryable< Entity > is a great way to re-use queries as you should neve rneed to copy and paste query fragments around your application, hope that helps.

Answer 3

Here's a suggestion: http://jerrytech.blogspot.com/2010/06/soa-implementation-of-entity-framework.html