Add flexible configuration option that allows to ignore legacy migrations

README.md

@@ -56,6 +56,16 @@ end
 
 The `with_lock` method will be useful when hitting the caveats of `LOCK=NONE`. Please read the 'Caveats' section.
 
+### Turn it off for old migrations
+
+Set up ignore based on version rule. Usually in your `config/application.rb`, something like that:
+
+```ruby
+config.active_record.mysql_online_migrations_ignore = -> (version) { version < "20141024152412" }
+```
+
+This will ignore all migrations before version `20141024152412`.
+
 ### Enable verbose output
 To enable an 'ONLINE MIGRATION' debug statement whenever an online migration is
 run, simply set the `MysqlOnlineMigrations.verbose` module variable to true.

lib/mysql_online_migrations.rb

@@ -13,10 +13,15 @@ class << self; attr_accessor :verbose; end
   def self.prepended(base)
     ActiveRecord::Base.send(:class_attribute, :mysql_online_migrations, :instance_writer => false)
     ActiveRecord::Base.send("mysql_online_migrations=", true)
+
+    ActiveRecord::Base.send(:class_attribute, :mysql_online_migrations_ignore, :instance_writer => false)
+    ActiveRecord::Base.send("mysql_online_migrations_ignore=", -> (version) { false })
   end
 
   def connection
     original_connection = super
+    return original_connection if ActiveRecord::Base.mysql_online_migrations_ignore.call(version)
+
     adapter_mode = original_connection.class.name == "ActiveRecord::ConnectionAdapters::Mysql2Adapter"
 
     @original_adapter ||= if adapter_mode

spec/lib/migration/version_ignore_spec.rb

@@ -0,0 +1,32 @@
+require "spec_helper"
+
+RSpec.describe ActiveRecord::Migration do
+  OLD_VERSION = "20120508133018"
+  NEW_VERSION = "20150119090054"
+
+  let(:comma_before_lock_none) { true }
+  let(:migration_arguments_with_lock) { [] }
+
+  context "#create_table" do
+    let(:method_name) { :create_table }
+    let(:migration_arguments) do
+      [
+        [:test5]
+      ]
+    end
+
+    context "when version ignore rule is configured" do
+      before { set_ignore_setting -> (version) { version < NEW_VERSION } }
+
+      context "when version matches" do
+        it_behaves_like "a migration that does not modify statement", OLD_VERSION
+        it_behaves_like "a migration that succeeds in MySQL", OLD_VERSION
+      end
+
+      context "when version does not match" do
+        it_behaves_like "a migration that adds LOCK=NONE when needed", NEW_VERSION
+        it_behaves_like "a migration that succeeds in MySQL", NEW_VERSION
+      end
+    end
+  end
+end

spec/support/helpers.rb

@@ -1,15 +1,18 @@
 module Helpers
   CATCH_STATEMENT_REGEX = /^(alter|create|drop|update|rename) /i
   DDL_STATEMENT_REGEX  = /^(alter|create (unique )? ?index|drop index) /i
+  DEFAULT_VERSION = "20110603153213"
 
-  def build_migration(method_name, args, &block)
+  def build_migration(method_name, args, version=nil, &block)
+    version ||= DEFAULT_VERSION
     migration = ActiveRecord::Migration.new
     migration.instance_variable_set(:@test_method_name, method_name)
     migration.instance_variable_set(:@test_args, args)
     migration.instance_variable_set(:@test_block, block)
     migration.define_singleton_method(:change) do
       public_send(@test_method_name, *@test_args, &@test_block)
     end
+    migration.version = version
     migration
   end
 
@@ -99,6 +102,10 @@ def set_ar_setting(value)
     allow(ActiveRecord::Base).to receive(:mysql_online_migrations).and_return(value)
   end
 
+  def set_ignore_setting(value)
+    allow(ActiveRecord::Base).to receive(:mysql_online_migrations_ignore).and_return(value)
+  end
+
   def teardown
     @adapter.drop_table :testing rescue nil
     @adapter.drop_table :test_rake rescue nil
@@ -112,4 +119,4 @@ def insert_version(version)
   def clear_version
     @adapter_without_lock.execute("TRUNCATE schema_migrations")
   end
-end
+end

spec/support/shared_examples/migration.rb

@@ -9,7 +9,7 @@ def staged_for_travis
   set_ar_setting(true) if ENV["TRAVIS"]
 end
 
-shared_examples_for "a migration that adds LOCK=NONE when needed" do
+shared_examples_for "a migration that adds LOCK=NONE when needed" do |version=nil|
   before(:each) do
     stub_adapter_without_lock
     stub_execute(@adapter, :execute, :regular_execute)
@@ -28,7 +28,7 @@ def staged_for_travis
       end
 
       begin
-        build_migration(method_name, migration_argument).migrate(:up)
+        build_migration(method_name, migration_argument, version).migrate(:up)
       rescue => e
         raise e unless @rescue_statement_when_stubbed
       end
@@ -42,23 +42,58 @@ def staged_for_travis
   end
 end
 
-shared_examples_for "a migration that succeeds in MySQL" do
+shared_examples_for "a migration that does not modify statement" do |version=nil|
+  before(:each) do
+    stub_adapter_without_lock
+    stub_execute(@adapter, :execute, :regular_execute)
+    stub_execute(@adapter_without_lock, :original_execute, :execute_without_lock)
+    @migration_arguments = migration_arguments + migration_arguments_with_lock
+  end
+
+  it "executes the same query as the original adapter unmodified" do
+    @migration_arguments.each do |migration_argument|
+      reset_queries_collectors
+
+      begin
+        @adapter.public_send(method_name, *migration_argument)
+      rescue => e
+        raise e unless @rescue_statement_when_stubbed
+      end
+
+      begin
+        build_migration(method_name, migration_argument, version).migrate(:up)
+      rescue => e
+        raise e unless @rescue_statement_when_stubbed
+      end
+
+      expect(@queries_received_by_regular_adapter.length).to be > 0
+      expect(@queries_received_by_adapter_without_lock.length).to eq(0)
+
+      size = @queries_received_by_regular_adapter.count
+      @queries_received_by_regular_adapter.each_with_index do |query, index|
+        expect(@queries_received_by_regular_adapter[size - index - 1]).to eq(query)
+      end
+    end
+  end
+end
+
+shared_examples_for "a migration that succeeds in MySQL" do |version=nil|
   it "succeeds without exception" do
     staged_for_travis do
       migration_arguments.each do |migration_argument|
-        migration = build_migration(method_name, migration_argument)
+        migration = build_migration(method_name, migration_argument, version)
         migration.migrate(:up)
         rebuild_table
       end
     end
   end
 end
 
-shared_examples_for "a migration with a non-lockable statement" do
+shared_examples_for "a migration with a non-lockable statement" do |version=nil|
   it "raises a MySQL exception" do
     staged_for_travis do
       migration_arguments_with_lock.each do |migration_argument|
-        migration = build_migration(method_name, migration_argument)
+        migration = build_migration(method_name, migration_argument, version)
         begin
           migration.migrate(:up)
         rescue ActiveRecord::StatementInvalid => e
@@ -68,4 +103,4 @@ def staged_for_travis
       end
     end
   end
-end
+end