Merge pull request #11 from freshworks/v2-lhm-trigger-drop-on-migrati…

…on-fix

[FD-120307] : LHM Trigger Drop Fix

lib/lhm/connection.rb

@@ -142,6 +142,15 @@ def execute(sql)
       def table_exists?(table_name)
         @adapter.table_exists?(table_name)
       end
+
+      def trigger_exists?(table_name, trigger_name)
+        !!select_one(%Q{
+          select trigger_name
+            from information_schema.triggers
+           where event_object_table='#{table_name}'
+             and trigger_name like '#{trigger_name}'
+        })
+      end
     end
   end
 end

lib/lhm/invoker.rb

@@ -6,6 +6,7 @@
 require 'lhm/atomic_switcher'
 require 'lhm/locked_switcher'
 require 'lhm/migrator'
+require 'lhm/trigger_switcher'
 
 module Lhm
   # Copies an origin table to an altered destination table. Live activity is
@@ -16,9 +17,10 @@ module Lhm
   class Invoker
     include SqlHelper
 
-    attr_reader :migrator, :connection
+    attr_reader :migrator, :connection, :origin
 
     def initialize(origin, connection)
+      @origin = origin
       @connection = connection
       @migrator = Migrator.new(origin, connection)
     end
@@ -40,8 +42,9 @@ def run(options = {})
         Chunker.new(migration, @connection, options).run
         if options[:atomic_switch]
           AtomicSwitcher.new(migration, @connection).run
+          TriggerSwitcher.new.copy_triggers(@origin, migration.archive_name, @connection) if options[:retain_triggers]
         else
-          LockedSwitcher.new(migration, @connection).run
+          LockedSwitcher.new(migration, @connection, options[:retain_triggers]).run
         end
       end
     end

lib/lhm/locked_switcher.rb

@@ -4,6 +4,7 @@
 require 'lhm/command'
 require 'lhm/migration'
 require 'lhm/sql_helper'
+require 'lhm/trigger_switcher'
 
 module Lhm
   # Switches origin with destination table nonatomically using a locked write.
@@ -22,25 +23,38 @@ class LockedSwitcher
 
     attr_reader :connection
 
-    def initialize(migration, connection = nil)
+    def initialize(migration, connection = nil, retain_triggers = false)
       @migration = migration
       @connection = connection
       @origin = migration.origin
       @destination = migration.destination
+      @retain_triggers = retain_triggers
     end
 
     def statements
       uncommitted { switch }
     end
 
     def switch
-      [
+      queries = [
         "lock table `#{ @origin.name }` write, `#{ @destination.name }` write",
         "alter table `#{ @origin.name }` rename `#{ @migration.archive_name }`",
         "alter table `#{ @destination.name }` rename `#{ @origin.name }`",
         "commit",
         "unlock tables"
       ]
+      if @retain_triggers
+        trigger_copy_queries = []
+        trigger_copy_queries << "lock table `#{ @migration.archive_name }` write, `#{ @origin.name }` write"
+        @origin.triggers.each do |trigger|
+          trigger_name = trigger[0]
+          trigger_copy_queries << "DROP TRIGGER #{trigger_name};"
+          trigger_copy_queries << TriggerSwitcher.new.fetch_trigger_definition(trigger_name, connection)
+        end
+        target_index = queries.index('commit')
+        queries.insert(target_index, *trigger_copy_queries) if trigger_copy_queries.length > 0 # inserting the trigger queries before commit query
+      end
+      queries
     end
 
     def uncommitted(&block)

lib/lhm/table.rb

@@ -6,11 +6,13 @@
 module Lhm
   class Table
     attr_reader :name, :columns, :indices, :pk, :ddl
+    attr_accessor :triggers
 
     def initialize(name, pk = "id", ddl = nil)
       @name = name
       @columns = {}
       @indices = {}
+      @triggers = []
       @pk = valid_primary_key(pk)
       @ddl = ddl
     end
@@ -69,11 +71,18 @@ def parse
           extract_indices(read_indices).each do |idx, columns|
             table.indices[idx] = columns
           end
+
+          table.triggers = read_triggers
         end
       end
 
     private
 
+      def read_triggers
+        sql = "show triggers where `table`= '#{@table_name}';"
+        @connection.execute(sql)
+      end
+
       def read_information_schema
         @connection.select_all %Q{
           select *

lib/lhm/trigger_switcher.rb

@@ -0,0 +1,36 @@
+module Lhm
+  class TriggerSwitcher
+    def copy_triggers(source_table, destination_table_name, connection)
+      return unless !destination_table_name.empty? && connection.table_exists?(destination_table_name)
+
+      source_table.triggers.each do |trigger|
+        trigger_name = trigger[0]
+        trigger_definition = fetch_trigger_definition(trigger_name, connection)
+        # since source table is renamed to lhma_table_name(destination table name) after migration, triggers associated with the source table will now be associated with lhma_table_name.
+        # skip if the trigger isn't associated with lhma_table_name.
+        next unless trigger_definition.include? destination_table_name
+
+        old_trigger_name = trigger_name
+        trigger_name = remove_timestamp_from_trigger_name_if_exists(trigger_name)
+        modified_trigger_name = trigger_name + '_' + Time.now.getutc.to_s.gsub(/[:\- ]/, '_') #sample trigger name - trigger_name_2023_12_18_03_40_45_UTC
+        modified_definition = trigger_definition.gsub(destination_table_name, source_table.name)
+        modified_definition = modified_definition.gsub(old_trigger_name, modified_trigger_name)
+        connection.execute(modified_definition)
+        connection.execute("DROP TRIGGER #{old_trigger_name};")
+      end
+    end
+
+    def fetch_trigger_definition(trigger_name, connection)
+      result = connection.execute("SHOW CREATE TRIGGER #{trigger_name};").first
+      # sample result => ["update_message_old_5", "NO_ENGINE_SUBSTITUTION", "CREATE DEFINER=`root`@`localhost` TRIGGER update_message_old_5 BEFORE INSERT ON `lhma_2023_09_04_14_32_54_810_logs_table` FOR EACH ROW\n BEGIN\n IF NEW.message = '1' THEN\n SET NEW.message = 'true';\n END IF;\n END", "utf8", "utf8_general_ci", "utf8_unicode_ci", 2023-09-04 14:32:43 UTC]
+      # create trigger definition will be stored in the third index in the result, ideally result will always be of length 7 if its executed successfully.
+      result && result.length > 2 ? result[2] : ''
+    end
+
+    def remove_timestamp_from_trigger_name_if_exists(trigger_name)
+      timestamp_suffix_regex = /_(\d{4}_\d{2}_\d{2}_\d{2}_\d{2}_\d{2}_UTC)\z/
+      match_data = trigger_name.match(/^(.*?)(?:#{timestamp_suffix_regex})$/)
+      match_data ? match_data[1] : trigger_name
+    end
+  end
+end

spec/integration/integration_helper.rb

@@ -124,6 +124,22 @@ def table_exists?(table)
     connection.table_exists?(table.name)
   end
 
+  def trigger_exists?(table_name, trigger_name)
+    connection.trigger_exists?(table_name, trigger_name)
+  end
+
+  def check_and_create_trigger_on_users_table
+    table_name = 'users'
+    trigger_name = 'timestamp_trigger'
+    unless trigger_exists?(table_name, trigger_name)
+      query = "CREATE TRIGGER #{trigger_name} BEFORE INSERT ON #{table_name} FOR EACH ROW
+             BEGIN
+              SET NEW.created_at = NOW();
+             END;"
+      execute query
+    end
+  end
+
   #
   # Database Helpers
   #

spec/integration/lhm_spec.rb

@@ -29,6 +29,59 @@
       end
     end
 
+    it "should retain triggers while migration if retain_triggers is set to true in atomic switch" do
+      table_name = 'users'
+      trigger_name = 'timestamp_trigger'
+      check_and_create_trigger_on_users_table
+      Lhm.change_table(table_name.to_sym, :atomic_switch => true, :cleanup => true, :retain_triggers => true) do |t|
+        t.add_column(:logins, "INT(12) DEFAULT '0'")
+      end
+
+      slave do
+        trigger_exists?(table_name, trigger_name).must_equal true
+      end
+    end
+
+    it "should retain triggers while migration if retain_triggers is set to true in locked switch" do
+      table_name = 'users'
+      trigger_name = 'timestamp_trigger'
+      check_and_create_trigger_on_users_table
+      Lhm.change_table(table_name.to_sym, :atomic_switch => false, :cleanup => true, :retain_triggers => true) do |t|
+        t.add_column(:logins, "INT(12) DEFAULT '0'")
+      end
+
+      slave do
+        trigger_exists?(table_name, trigger_name).must_equal true
+      end
+    end
+
+    it "should not retain triggers while migration if retain_triggers is set to false" do
+      table_name = 'users'
+      trigger_name = 'timestamp_trigger'
+      check_and_create_trigger_on_users_table
+      Lhm.change_table(table_name.to_sym, :atomic_switch => false, :cleanup => true, :retain_triggers => false) do |t|
+        t.add_column(:logins_1, "INT(12) DEFAULT '0'")
+      end
+
+      slave do
+        trigger_exists?(table_name, trigger_name).must_equal false
+      end
+    end
+
+    it "should not retain triggers while migration if retain_triggers is not passed in the options" do
+      table_name = 'users'
+      trigger_name = 'timestamp_trigger'
+      check_and_create_trigger_on_users_table
+      Lhm.change_table(table_name.to_sym, :atomic_switch => false, :cleanup => true) do |t|
+        t.add_column(:logins_2, "INT(12) DEFAULT '0'")
+      end
+
+      slave do
+        trigger_exists?(table_name, trigger_name).must_equal false
+      end
+    end
+
+
     it "should copy all rows" do
       23.times { |n| execute("insert into users set reference = '#{ n }'") }