Directly use ActiveRecord object instead of ID

This change will improve the performance by reducing unnecessary SELECT queries.

app/controllers/concerns/file_parameters.rb

@@ -8,7 +8,7 @@ module FileParameters
         next true if file.nil? || file.hidden || file.read_only
         # avoid that public files from other contexts can be created
         # `next` is similar to an early return and will proceed with the next iteration of the loop
-        next true if file.context_type == 'Exercise' && file.context_id != exercise.id
+        next true if file.context_type == 'Exercise' && file.context != exercise
         next true if file.context_type == 'Submission' && file.context.user != current_user
         next true if file.context_type == 'CommunitySolution' && controller_name != 'community_solutions'
 

app/controllers/concerns/submission_parameters.rb

@@ -21,9 +21,8 @@ module SubmissionParameters
   def merge_user(params)
     # The study_group_id might not be present in the session (e.g. for internal users), resulting in session[:study_group_id] = nil which is intended.
     params.merge(
-      user_id: current_user.id,
-      user_type: current_user.class.name,
-      study_group_id: session[:study_group_id]
+      user: current_user,
+      study_group_id: current_user.current_study_group_id
     )
   end
 end