Fixes #3472 - Mentions migration fails because of unexpected User notification_config matrix state.

db/migrate/20201110000001_mention_init.rb

@@ -18,7 +18,7 @@ class MentionInit < ActiveRecord::Migration[5.2]
 
     Mention.reset_column_information
     create_overview
-    update_user_matrix
+    update_users
   end
 
   def create_overview
@@ -43,24 +43,32 @@ class MentionInit < ActiveRecord::Migration[5.2]
     )
   end
 
-  def update_user_matrix
+  def update_users
     User.with_permissions('ticket.agent').each do |user|
       next if user.preferences.blank?
       next if user.preferences['notification_config'].blank?
       next if user.preferences['notification_config']['matrix'].blank?
 
-      update_user_matrix_by_user(user)
+      update_matrix(user.preferences['notification_config']['matrix'])
+
+      user.save!
     end
   end
 
-  def update_user_matrix_by_user(user)
-    %w[create update].each do |type|
-      user.preferences['notification_config']['matrix'][type]['criteria']['subscribed'] = true
+  def update_matrix(matrix)
+    matrix_type_defaults.each do |type, default|
+      matrix[type] ||= {}
+      matrix[type]['criteria'] ||= {}
+      matrix[type]['criteria']['subscribed'] = default
     end
+  end
 
-    %w[reminder_reached escalation].each do |type|
-      user.preferences['notification_config']['matrix'][type]['criteria']['subscribed'] = false
-    end
-    user.save!
+  def matrix_type_defaults
+    @matrix_type_defaults ||= {
+      'create'           => true,
+      'update'           => true,
+      'reminder_reached' => false,
+      'escalation'       => false,
+    }
   end
 end

spec/db/migrate/mention_init_spec.rb

@@ -0,0 +1,67 @@
+require 'rails_helper'
+
+RSpec.describe MentionInit, type: :db_migration do
+
+  let(:mocked_table_actions) do
+    lambda { |migration|
+      # mock DB connection with null object to "null" all connection actions
+      allow(migration).to receive(:connection).and_return(double('ActiveRecord::ConnectionAdapters::*').as_null_object) # rubocop:disable RSpec/VerifiedDoubles
+    }
+  end
+
+  context 'when agent is present' do
+
+    subject(:user) do
+      agent = create(:agent)
+      agent.preferences['notification_config'] = notification_config
+      agent.tap(&:save!)
+    end
+
+    context 'when matrix misses type key' do
+
+      let(:notification_config) do
+        {
+          'matrix' => {
+            'create'           => {
+              'criteria' => {
+                'subscribed' => true
+              }
+            },
+            'update'           => {
+              # 'criteria' => {
+              #   'subscribed' => true
+              # }
+            },
+            'reminder_reached' => {
+              'criteria' => {
+                'subscribed' => false
+              }
+            },
+            'escalation'       => {
+              'criteria' => {
+                'subscribed' => false
+              }
+            },
+          }
+        }
+      end
+
+      it 'adds type' do # rubocop:disable RSpec/ExampleLength
+        expect do
+          migrate(&mocked_table_actions)
+        end
+          .to change {
+                user.reload.preferences['notification_config']['matrix']['update']
+              }
+          .from({})
+          .to(
+            {
+              'criteria' => {
+                'subscribed' => true
+              }
+            }
+          )
+      end
+    end
+  end
+end