1 files changed, 46 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/internal_metadata.rb b/activerecord/lib/active_record/internal_metadata.rb
new file mode 100644
index 0000000000..e5c6e5c885
--- /dev/null
+++ b/activerecord/lib/active_record/internal_metadata.rb
@@ -0,0 +1,46 @@
+require 'active_record/scoping/default'
+require 'active_record/scoping/named'
+
+module ActiveRecord
+  # This class is used to create a table that keeps track of values and keys such
+  # as which environment migrations were run in.
+  class InternalMetadata < ActiveRecord::Base # :nodoc:
+    class << self
+      def primary_key
+        "key"
+      end
+
+      def table_name
+        "#{table_name_prefix}#{ActiveRecord::Base.internal_metadata_table_name}#{table_name_suffix}"
+      end
+
+      def index_name
+        "#{table_name_prefix}unique_#{ActiveRecord::Base.internal_metadata_table_name}#{table_name_suffix}"
+      end
+
+      def []=(key, value)
+        first_or_initialize(key: key).update_attributes!(value: value)
+      end
+
+      def [](key)
+        where(key: key).pluck(:value).first
+      end
+
+      def table_exists?
+        ActiveSupport::Deprecation.silence { connection.table_exists?(table_name) }
+      end
+
+      # Creates an internal metadata table with columns +key+ and +value+
+      def create_table
+        unless table_exists?
+          connection.create_table(table_name, id: false) do |t|
+            t.column :key,   :string
+            t.column :value, :string
+            t.timestamps
+            t.index  :key, unique: true, name: index_name
+          end
+        end
+      end
+    end
+  end
+end