raise error for pending migration

can be configured by setting config.active_record.migration. Setting to :page_load will raise an error on each page refresh if there are migrations that are pending. Setting to :page_load is defaulted in development for new applications. 

2 files changed, 33 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 2975b045e7..a0169203b0 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -32,6 +32,12 @@ module ActiveRecord
     end
   end
 
+  class PendingMigrationError < ActiveRecordError#:nodoc:
+    def initialize
+      super("Migrations are pending run 'bundle exec rake db:migrate RAILS_ENV=#{ENV['RAILS_ENV']}' to resolve the issue")
+    end
+  end
+
   # = Active Record Migrations
   #
   # Migrations can manage the evolution of a schema used by several physical
@@ -326,10 +332,28 @@ module ActiveRecord
   class Migration
     autoload :CommandRecorder, 'active_record/migration/command_recorder'
 
+
+    # This class is used to verify that all migrations have been run before
+    # loading a web page if config.active_record.migration_error is set to :page_load
+    class CheckPending
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        ActiveRecord::Migration.check_pending!
+        status, headers, body = @app.call(env)
+      end
+    end
+
     class << self
       attr_accessor :delegate # :nodoc:
     end
 
+    def self.check_pending!
+      raise ActiveRecord::PendingMigrationError if ActiveRecord::Migrator::needs_migrations?
+    end
+
     def self.method_missing(name, *args, &block) # :nodoc:
       (delegate || superclass.delegate).send(name, *args, &block)
     end
@@ -605,8 +629,8 @@ module ActiveRecord
         end
       end
 
-      def needs_migration?
-        current_version != last_version
+      def needs_migrations?
+        current_version < last_version
       end
 
       def last_version
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 1e497b2a79..319516413b 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -59,6 +59,13 @@ module ActiveRecord
       ActiveSupport.on_load(:active_record) { self.logger ||= ::Rails.logger }
     end
 
+    initializer "active_record.migration_error" do |app|
+      if config.active_record.delete(:migration_error) == :page_load
+        config.app_middleware.insert_after "::ActionDispatch::Callbacks",
+          "ActiveRecord::Migration::CheckPending"
+      end
+    end
+
     initializer "active_record.set_configs" do |app|
       ActiveSupport.on_load(:active_record) do
         if app.config.active_record.delete(:whitelist_attributes)