don't try and eager load in a data fixup

fixes CNVS-21318

eager load will try and select all the columns of the joined table by
name. but due to race conditions, being in the middle of running
migrations, it's possible the process will know of a column that hasn't
been created yet. naming it in the select will break the query.

Change-Id: I71ddd01c77f8f6157e36a01103dff52b7b967284
test-plan: N/A
Reviewed-on: https://gerrit.instructure.com/63902
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Product-Review: Jacob Fugal <jacob@instructure.com>
QA-Review: Jacob Fugal <jacob@instructure.com>

gems/rubocop-canvas/lib/rubocop_canvas/cops/datafixup/eager_load.rb

@@ -0,0 +1,17 @@
+module RuboCop
+  module Cop
+    module Datafixup
+      class EagerLoad < Cop
+        def on_send(node)
+          _receiver, method_name, *_args = *node
+          if method_name.to_s == 'eager_load'
+            add_offense(node,
+              :expression,
+              "eager_load in a data fixup causes errors",
+              :error)
+          end
+        end
+      end
+    end
+  end
+end

lib/data_fixup/exclude_deleted_entries_from_unread_count.rb

@@ -2,7 +2,7 @@ module DataFixup::ExcludeDeletedEntriesFromUnreadCount
   def self.run
     # Deleted all partipant entries for deleted discussion entries
     DiscussionEntryParticipant.
-        eager_load(:discussion_entry).
+        joins(:discussion_entry).preload(:discussion_entry).readonly(false).
         where(:discussion_entries => { :workflow_state => 'deleted' }).
         destroy_all
 

lib/data_fixup/fix_invalid_course_ids_on_enrollments.rb

@@ -1,6 +1,6 @@
 module DataFixup::FixInvalidCourseIdsOnEnrollments
   def self.run
-    Enrollment.joins(:course_section).eager_load(:course_section).
+    Enrollment.joins(:course_section).preload(:course_section).
       where("course_sections.course_id<>enrollments.course_id").
       find_each do |e|
       Enrollment.where(id: e).update_all(course_id: e.course_section.course_id)