1 files changed, 50 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..4e8932a695
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -0,0 +1,50 @@
+module ActiveRecord
+  module ConnectionAdapters
+    class SchemaCache
+      attr_reader :columns, :columns_hash, :primary_keys, :tables
+      attr_reader :connection
+
+      def initialize(conn)
+        @connection = conn
+        @tables     = {}
+
+        @columns = Hash.new do |h, table_name|
+          h[table_name] = conn.columns(table_name, "#{table_name} Columns")
+        end
+
+        @columns_hash = Hash.new do |h, table_name|
+          h[table_name] = Hash[columns[table_name].map { |col|
+            [col.name, col]
+          }]
+        end
+
+        @primary_keys = Hash.new do |h, table_name|
+          h[table_name] = table_exists?(table_name) ? conn.primary_key(table_name) : nil
+        end
+      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
+
+      # Clears out internal caches
+      def clear!
+        @columns.clear
+        @columns_hash.clear
+        @primary_keys.clear
+        @tables.clear
+      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
+    end
+  end
+end