cache column defaults for AR object instantiation

activerecord/lib/active_record/base.rb

@@ -710,6 +710,12 @@ module ActiveRecord #:nodoc:
         connection_pool.columns_hash[table_name]
       end
 
+      # Returns a hash where the keys are column names and the values are
+      # default values when instantiating the AR object for this table.
+      def column_defaults
+        connection_pool.column_defaults[table_name]
+      end
+
       # Returns an array of column names as strings.
       def column_names
         @column_names ||= columns.map { |column| column.name }

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -60,6 +60,7 @@ module ActiveRecord
       attr_accessor :automatic_reconnect
       attr_reader :spec, :connections
       attr_reader :columns, :columns_hash, :primary_keys, :tables
+      attr_reader :column_defaults
 
       # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification
       # object which describes database connection information (e.g. adapter,
@@ -106,6 +107,12 @@ module ActiveRecord
           }]
         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] = with_connection do |conn|
             table_exists?(table_name) ? conn.primary_key(table_name) : 'id'
@@ -133,6 +140,7 @@ module ActiveRecord
       def clear_cache!
         @columns.clear
         @columns_hash.clear
+        @column_defaults.clear
         @tables.clear
       end
 
@@ -140,6 +148,7 @@ module ActiveRecord
       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
 

activerecord/lib/active_record/persistence.rb

@@ -317,9 +317,7 @@ module ActiveRecord
     # that a new instance, or one populated from a passed-in Hash, still has all the attributes
     # that instances loaded from the database would.
     def attributes_from_column_definition
-      Hash[self.class.columns.map do |column|
-        [column.name, column.default]
-      end]
+      self.class.column_defaults.dup
     end
   end
 end