Performance: cache/reload arel relation when possible to speed up things.

activerecord/lib/active_record/base.rb

@@ -2602,7 +2602,7 @@ def delete
       # be made (since they can't be persisted).
       def destroy
         unless new_record?
-          arel_table.where(arel_table[self.class.primary_key].eq(id)).delete
+          arel_table(true).where(arel_table[self.class.primary_key].eq(id)).delete
         end
 
         freeze
@@ -2904,7 +2904,7 @@ def create_or_update
       def update(attribute_names = @attributes.keys)
         attributes_with_values = arel_attributes_values(false, false, attribute_names)
         return 0 if attributes_with_values.empty?
-        arel_table.where(arel_table[self.class.primary_key].eq(id)).update(attributes_with_values)
+        arel_table(true).where(arel_table[self.class.primary_key].eq(id)).update(attributes_with_values)
       end
 
       # Creates a record with values matching those of the instance attributes
@@ -2991,8 +2991,9 @@ def attributes_protected_by_default
         default
       end
 
-      def arel_table
-        @arel_table = Arel::Table.new(self.class.table_name)
+      def arel_table(reload = nil)
+        @arel_table = Relation.new(self, self.class.table_name) if reload || @arel_table.nil?
+        @arel_table
       end
 
       # Returns a copy of the attributes hash where all the values have been safely quoted for use in

activerecord/lib/active_record/locking/optimistic.rb

@@ -89,7 +89,7 @@ def update_with_lock(attribute_names = @attributes.keys) #:nodoc:
           attribute_names.uniq!
 
           begin
-            affected_rows = arel_table.where(
+            affected_rows = arel_table(true).where(
               arel_table[self.class.primary_key].eq(quoted_id).and(
                 arel_table[self.class.locking_column].eq(quote_value(previous_value))
               )
@@ -116,7 +116,7 @@ def destroy_with_lock #:nodoc:
       lock_col = self.class.locking_column
       previous_value = send(lock_col).to_i
 
-      affected_rows = arel_table.where(
+      affected_rows = arel_table(true).where(
           arel_table[self.class.primary_key].eq(quoted_id).and(
           arel_table[self.class.locking_column].eq(quote_value(previous_value))
         )