1 files changed, 72 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..b14b37ce89
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -0,0 +1,72 @@
+module ActiveRecord
+  module ConnectionAdapters
+    class SchemaCache
+      attr_reader :columns, :columns_hash, :primary_keys, :tables
+      attr_reader :column_defaults
+      attr_reader :connection
+
+      def initialize(conn)
+        @connection = conn
+        @tables              = {}
+
+        @columns     = Hash.new do |h, table_name|
+          h[table_name] =
+            # Fetch a list of columns
+            conn.columns(table_name, "#{table_name} Columns").tap do |cs|
+              # set primary key information
+              cs.each do |column|
+                column.primary = column.name == primary_keys[table_name]
+              end
+            end
+        end
+
+        @columns_hash = Hash.new do |h, table_name|
+          h[table_name] = Hash[columns[table_name].map { |col|
+            [col.name, col]
+          }]
+        end
+
+        @column_defaults = Hash.new do |h, table_name|
+          h[table_name] = Hash[columns[table_name].map { |col|
+            [col.name, col.default]
+          }]
+        end
+
+        @primary_keys = Hash.new do |h, table_name|
+          h[table_name] = table_exists?(table_name) ?
+                          conn.primary_key(table_name) : 'id'
+        end
+      end
+
+      # A cached lookup for table existence.
+      def table_exists?(name)
+        return @tables[name] if @tables.key? name
+
+        connection.tables.each { |table| @tables[table] = true }
+        @tables[name] = connection.table_exists?(name) if !@tables.key?(name)
+
+        @tables[name]
+      end
+
+      # Clears out internal caches:
+      #
+      #   * columns
+      #   * columns_hash
+      #   * tables
+      def clear!
+        @columns.clear
+        @columns_hash.clear
+        @column_defaults.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
+        @column_defaults.delete table_name
+        @primary_keys.delete table_name
+      end
+    end
+  end
+end