From 838e18321118ee3ec6669217e5ea0216f79c969a Mon Sep 17 00:00:00 2001
From: Jeremy McNevin <jeremy.mcnevin@novu.com>
Date: Wed, 30 Jul 2014 14:10:28 -0500
Subject: [PATCH] Correctly determine if migration is needed.

This method would assume that if last migration in the migrations
directory matched the current schema version, that the database was up
to date, but this does not account for new migrations with older
timestamps that may be pending.
---
 activerecord/lib/active_record/migration.rb | 19 +++++++++----------
 activerecord/test/cases/migration_test.rb   | 15 +++++++++++++++
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index a6847e28c2..659c5e3bbb 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -836,21 +836,20 @@ module ActiveRecord
         SchemaMigration.table_name
       end
 
-      def get_all_versions
-        SchemaMigration.all.map { |x| x.version.to_i }.sort
-      end
-
-      def current_version(connection = Base.connection)
-        sm_table = schema_migrations_table_name
-        if connection.table_exists?(sm_table)
-          get_all_versions.max || 0
+      def get_all_versions(connection = Base.connection)
+        if connection.table_exists?(schema_migrations_table_name)
+          SchemaMigration.all.map { |x| x.version.to_i }.sort
         else
-          0
+          []
         end
       end
 
+      def current_version(connection = Base.connection)
+        get_all_versions(connection).max || 0
+      end
+
       def needs_migration?(connection = Base.connection)
-        current_version(connection) < last_version
+        (migrations(migrations_paths).collect(&:version) - get_all_versions(connection)).size > 0
       end
 
       def last_version
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index ef3f073472..8176e82f10 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -81,6 +81,21 @@ class MigrationTest < ActiveRecord::TestCase
     assert_equal 0, ActiveRecord::Migrator.current_version
     assert_equal 3, ActiveRecord::Migrator.last_version
     assert_equal true, ActiveRecord::Migrator.needs_migration?
+
+    ActiveRecord::SchemaMigration.create!(:version => ActiveRecord::Migrator.last_version)
+    assert_equal true, ActiveRecord::Migrator.needs_migration?
+  ensure
+    ActiveRecord::Migrator.migrations_paths = old_path
+  end
+
+  def test_migration_detection_without_schema_migration_table
+    ActiveRecord::Base.connection.drop_table :schema_migrations
+
+    migrations_path = MIGRATIONS_ROOT + "/valid"
+    old_path = ActiveRecord::Migrator.migrations_paths
+    ActiveRecord::Migrator.migrations_paths = migrations_path
+
+    assert_equal true, ActiveRecord::Migrator.needs_migration?
   ensure
     ActiveRecord::Migrator.migrations_paths = old_path
   end