FIX: Don't allow NULL values for `notification_level` in `category_users` (#15407)

app/models/category_user.rb

@@ -243,7 +243,7 @@ end
 #  id                 :integer          not null, primary key
 #  category_id        :integer          not null
 #  user_id            :integer          not null
-#  notification_level :integer
+#  notification_level :integer          not null
 #  last_seen_at       :datetime
 #
 # Indexes

db/migrate/20211224111749_not_null_notification_level_in_category_users.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class NotNullNotificationLevelInCategoryUsers < ActiveRecord::Migration[6.1]
+  def change
+    up_only do
+      execute("DELETE FROM category_users WHERE notification_level IS NULL")
+    end
+    change_column_null :category_users, :notification_level, false
+  end
+end

spec/jobs/export_user_archive_spec.rb

@@ -331,7 +331,7 @@ describe Jobs::ExportUserArchive do
           .category_users
           .where(category_id: category_id)
           .first_or_initialize
-          .update!(last_seen_at: reset_at)
+          .update!(last_seen_at: reset_at, notification_level: NotificationLevels.all[:regular])
       end
 
       # Set Watching First Post on announcements, Tracking on subcategory, Muted on deleted, nothing on subsubcategory
@@ -355,7 +355,7 @@ describe Jobs::ExportUserArchive do
 
       expect(data[1][:category_id]).to eq(subsubcategory.id.to_s)
       expect(data[1][:category_names]).to eq("#{category.name}|#{subcategory.name}|#{subsubcategory.name}")
-      expect(data[1][:notification_level]).to eq('') # empty string, not 'normal'
+      expect(data[1][:notification_level]).to eq('regular')
       expect(DateTime.parse(data[1][:dismiss_new_timestamp])).to eq(reset_at)
 
       expect(data[2][:category_id]).to eq(announcements.id.to_s)

spec/models/topic_list_spec.rb

@@ -50,7 +50,11 @@ describe TopicList do
 
   describe '#load_topics' do
     it 'loads additional data for serialization' do
-      category_user = CategoryUser.create!(user: user, category: topic.category)
+      category_user = CategoryUser.create!(
+        user: user,
+        category: topic.category,
+        notification_level: NotificationLevels.all[:regular]
+      )
 
       topic = topic_list.load_topics.first
 

spec/models/topic_tracking_state_spec.rb

@@ -354,18 +354,6 @@ describe TopicTrackingState do
     expect(report.length).to eq(1)
   end
 
-  it "correctly handles category_users with null notification level" do
-    post
-
-    report = TopicTrackingState.report(user)
-    expect(report.length).to eq(1)
-
-    CategoryUser.create!(user_id: user.id, category_id: post.topic.category_id)
-
-    report = TopicTrackingState.report(user)
-    expect(report.length).to eq(1)
-  end
-
   it "works when categories are default muted" do
     SiteSetting.mute_all_categories_by_default = true