chore: Automate conversation display_id generation with db triggers (#1412)

Automate conversation display_id generation with db triggers

Co-authored-by: Saurabh Mehta <saurabh1.mehta@airtel.com>
Co-authored-by: Sojan Jose <sojan@pepalo.com>

db/migrate/20201125121240_create_triggers_accounts_insert_or_conversations_insert.rb

@@ -0,0 +1,27 @@
+# This migration was auto-generated via `rake db:generate_trigger_migration'.
+# While you can edit this file, any changes you make to the definitions here
+# will be undone by the next auto-generated trigger migration.
+
+class CreateTriggersAccountsInsertOrConversationsInsert < ActiveRecord::Migration[6.0]
+  def up
+    create_trigger('accounts_after_insert_row_tr', generated: true, compatibility: 1)
+      .on('accounts')
+      .after(:insert)
+      .for_each(:row) do
+      "execute format('create sequence IF NOT EXISTS conv_dpid_seq_%s', NEW.id);"
+    end
+
+    create_trigger('conversations_before_insert_row_tr', generated: true, compatibility: 1)
+      .on('conversations')
+      .before(:insert)
+      .for_each(:row) do
+      "NEW.display_id := nextval('conv_dpid_seq_' || NEW.account_id);"
+    end
+  end
+
+  def down
+    drop_trigger('accounts_after_insert_row_tr', 'accounts', generated: true)
+
+    drop_trigger('conversations_before_insert_row_tr', 'conversations', generated: true)
+  end
+end

db/migrate/20201125123131_conv_dpid_seq_for_existing_accnts.rb

@@ -0,0 +1,21 @@
+class ConvDpidSeqForExistingAccnts < ActiveRecord::Migration[6.0]
+  def up
+    ::Account.find_in_batches do |accounts_batch|
+      Rails.logger.info "migrated till #{accounts_batch.first.id}\n"
+      accounts_batch.each do |account|
+        display_id = Conversation.where(account_id: account.id).maximum('display_id')
+        display_id ||= 0 # for accounts with out conversations
+        ActiveRecord::Base.connection.exec_query("create sequence IF NOT EXISTS conv_dpid_seq_#{account.id} START #{display_id + 1}")
+      end
+    end
+  end
+
+  def down
+    ::Account.find_in_batches do |accounts_batch|
+      Rails.logger.info "migrated till #{accounts_batch.first.id}\n"
+      accounts_batch.each do |account|
+        ActiveRecord::Base.connection.exec_query("drop sequence IF EXISTS conv_dpid_seq_#{account.id}")
+      end
+    end
+  end
+end