Use ActiveRecord over Arrays for email lists

Signed-off-by: jonathan.kerr <3410350+jonodrew@users.noreply.github.com>

#member_emails previously processed an enormous array of objects in-memory. I've altered both that method and the underlying model to work solely in ActiveRecord, thereby reducing the memory strain.

Author: jonodrew

app/controllers/admin/chapters_controller.rb

@@ -67,8 +67,15 @@ def set_chapter
   end
 
   def member_emails(chapter, type)
-    return chapter.send(type).map(&:email).join("\n") if %w[students coaches].include?(type)
-
-    chapter.members.pluck(:email).uniq.join("\n")
+    members =
+      case type
+      when "students"
+        chapter.students
+      when "coaches"
+        chapter.coaches
+      else
+        chapter.members
+      end
+    members.distinct.pluck(:email).join("\n")
   end
 end

app/models/chapter.rb

@@ -34,11 +34,15 @@ def organisers
   end
 
   def students
-    members.select(&:student?)
+    Member.joins(:groups)
+          .merge(Group.students)
+          .distinct
   end
 
   def coaches
-    members.select(&:coach?)
+    Member.joins(:groups)
+          .merge(Group.coaches)
+          .distinct
   end
 
   private