1 files changed, 82 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
new file mode 100644
index 0000000000..aad1f9a7ef
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -0,0 +1,82 @@
+module ActiveRecord
+  module ConnectionAdapters
+    class SchemaCache
+      attr_reader :columns, :columns_hash, :primary_keys, :tables, :version
+      attr_accessor :connection
+
+      def initialize(conn)
+        @connection = conn
+
+        @columns      = {}
+        @columns_hash = {}
+        @primary_keys = {}
+        @tables       = {}
+        prepare_default_proc
+      end
+
+      # A cached lookup for table existence.
+      def table_exists?(name)
+        return @tables[name] if @tables.key? name
+
+        @tables[name] = connection.table_exists?(name)
+      end
+
+      # Add internal cache for table with +table_name+.
+      def add(table_name)
+        if table_exists?(table_name)
+          @primary_keys[table_name]
+          @columns[table_name]
+          @columns_hash[table_name]
+        end
+      end
+
+      # Clears out internal caches
+      def clear!
+        @columns.clear
+        @columns_hash.clear
+        @primary_keys.clear
+        @tables.clear
+        @version = nil
+      end
+
+      # Clear out internal caches for table with +table_name+.
+      def clear_table_cache!(table_name)
+        @columns.delete table_name
+        @columns_hash.delete table_name
+        @primary_keys.delete table_name
+        @tables.delete table_name
+      end
+
+      def marshal_dump
+        # if we get current version during initialization, it happens stack over flow.
+        @version = ActiveRecord::Migrator.current_version
+        [@version] + [:@columns, :@columns_hash, :@primary_keys, :@tables].map do |val|
+          self.instance_variable_get(val).inject({}) { |h, v| h[v[0]] = v[1]; h }
+        end
+      end
+
+      def marshal_load(array)
+        @version, @columns, @columns_hash, @primary_keys, @tables = array
+        prepare_default_proc
+      end
+
+      private
+
+      def prepare_default_proc
+        @columns.default_proc = Proc.new do |h, table_name|
+          h[table_name] = connection.columns(table_name)
+        end
+
+        @columns_hash.default_proc = Proc.new do |h, table_name|
+          h[table_name] = Hash[columns[table_name].map { |col|
+            [col.name, col]
+          }]
+        end
+
+        @primary_keys.default_proc = Proc.new do |h, table_name|
+          h[table_name] = table_exists?(table_name) ? connection.primary_key(table_name) : nil
+        end
+      end
+    end
+  end
+end