I have successfully added a new stored procedure to the database, and I also updated my .edmx-model. Whilst updating I found my new stored procedure.
However, when updating the database also updates NopObjectContext.Functions and NopObjectContext.ObjectSets, but the new stored procedure is not included.
1- Go to your designer NopModel.edmx and click right :"Update Model form database..."
2-Then, Click right on designer -> Add > Function Import
-> Function ImportName : Sp_yourprocedureName (because All the procedures of Nop are prefixed with Sp_ , so you can keep this naming logic)
-> Stored Procedure Name : Select your new stored procedure name
Select your return type of your procedure name. (NB: If you create a store procedure who return several field of several different tables , create une class whose inhereit BusinessEntity , with all the properties that return your procedure stored).
Click on Ok -> Recompile Nop.BusinessLogic and go to the end of the file NopObjectContext.Function.cs
-> your function was added with good signature and you can call it since your business logic library.