After getting insert/update/delete stored procedures going with a simple standalone table (no relationships), I started thinking about how I'd do this in a many-many relationship. Let's say that I have students and classes, with a many-many relationship represented by a studentclass table with only a student_id and class_id. EDM maps this to a many-many relationship, leaving the "join table" out of the conceptual model (no studentclass entity). That's what I'd want. But…how to map insert/update/delete on the studentclass table, because there is no entity for it?
Turns out that this is OK, because mapping insert/update/delete to sprocs is not exposed on the entity (CSD layer), but on the mapping (MSD) layer. And, sure enough, there is an ModificationFunctionMapping element exposed under AssociationSetMapping, as well as under EntityTypeMapping. The designer doesn't support this yet, but the raw XML schema does.
In addition, the Entity Framework "Help Overview" file does mention "Mapping Association Sets to stored procedures". It doesn't help matters by showing an example of Categories and Products in the Northwind sample database, where the Categories and Products tables don't have a many-many relationship or a join table. Do I *need* stored procedures on a zero-or-one-many relationship as well as on the "base" tables that comprise the relationship? I can insert and delete a relationship between an existing product and an existing category, so I might need these in addition to the stored procs mapping the base tables, in case these aren't already enforced by key constraints in the database and model? Doesn't seem like I'd need them at all, unless I specifically left the appropriate key constraints out of the database, but wanted them in the mapping and conceptual model.
But the Help Overview specifically mentions "mapped to a join table in a relationship", so many-many sounds like to the relationship type (AssociationSet cardinality) I'd need stored procedure mappings for.
So there IS a way to do it with many-many.