use safe_constantize to ignore unmappable assets

fixes CLAB-445
flag=none

Test plan:
- enable Smart Search feature flag
- go to course -> settings -> import course content
- choose 'Copy a Canvas course'
  and check 'Import existing quizzes as New Quizzes' checkbox
- click 'Import'
- the course copy should be success

Change-Id: I4c80af9f2d162b2d01e4118cecd94890c10ee6ff
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/355649
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Tamas Barna <tamas.barna@instructure.com>
Reviewed-by: Ferenc Marcsó <ferenc.marcso@instructure.com>
QA-Review: Tamas Barna <tamas.barna@instructure.com>
Product-Review: Peipei Zhou <peipei.zhou@instructure.com>

app/models/content_migration.rb

@@ -1393,8 +1393,8 @@ class ContentMigration < ActiveRecord::Base
     global_ids = master_template.present? || use_global_identifiers?
 
     migration_settings[:imported_assets].each do |asset_type, dest_ids|
-      klass = asset_type.constantize
-      next unless klass.column_names.include? "migration_id"
+      klass = asset_type.safe_constantize
+      next unless klass&.column_names&.include? "migration_id"
 
       dest_ids = dest_ids.split(",").map(&:to_i)
       mig_id_to_dest_id = context.shard.activate do

lib/smart_search.rb

@@ -232,7 +232,7 @@ module SmartSearch
                     SmartSearch.smart_search_available?(content_migration.context)
 
       content_migration.imported_asset_id_map&.each do |class_name, id_mapping|
-        klass = class_name.constantize
+        klass = class_name.safe_constantize
         next unless klass.respond_to?(:embedding_class)
 
         fk = klass.embedding_foreign_key # i.e. :wiki_page_id

spec/models/content_migration_spec.rb

@@ -2239,4 +2239,45 @@ describe ContentMigration do
       expect(@course.attachments.last.file_state).not_to eq("deleted")
     end
   end
+
+  context "imported_asset_id_map" do
+    before :once do
+      # not actually doing a course copy here, just simulating a finished one
+      @src = course_factory
+      @dst = course_factory
+      @old_assignment = @src.assignments.create! title: "foo"
+      @new_assignment = @dst.assignments.create! title: "foo", migration_id: CC::CCHelper.create_key(@old_assignment, global: true)
+
+      @old_wp = @src.wiki_pages.create! title: "bar"
+      @new_wp = @dst.wiki_pages.create!(
+        title: "bar",
+        migration_id: CC::CCHelper.create_key(@old_wp, global: true)
+      )
+
+      @cm = @dst.content_migrations.build(migration_type: "course_copy_importer", user: @teacher)
+      @cm.migration_settings[:imported_assets] = {
+        "Assignment" => @new_assignment.id.to_s,
+        "WikiPage" => @new_wp.id.to_s,
+      }
+      @cm.workflow_state = "imported"
+      @cm.source_course = @src
+      @cm.save!
+    end
+
+    it "returns a hash mapping the source asset IDs to the destination asset IDs" do
+      expect(@cm.imported_asset_id_map).to eq({
+                                                "Assignment" => { @old_assignment.id => @new_assignment.id },
+                                                "WikiPage" => { @old_wp.id => @new_wp.id }
+                                              })
+    end
+
+    it "ignores assets that can't be mapped" do
+      @cm.migration_settings[:imported_assets]["lti_assignment_quiz_set"] = []
+      @cm.save!
+      expect(@cm.imported_asset_id_map).to eq({
+                                                "Assignment" => { @old_assignment.id => @new_assignment.id },
+                                                "WikiPage" => { @old_wp.id => @new_wp.id }
+                                              })
+    end
+  end
 end