#NEWLINE# def _delete_null_columns( self ) : #NEWLINE# #INDENT# '\n        executes a delete query to remove columns that have changed to null\n        ' #NEWLINE# ds = DeleteStatement ( self . column_family_name , conditionals = self . _conditional , if_exists = self . _if_exists ) #NEWLINE# deleted_fields = False #NEWLINE# for ( _ , v ) in self . instance . _values . items ( ) : #NEWLINE# #INDENT# col = v . column #NEWLINE# if v . deleted : #NEWLINE# #INDENT# ds . add_field ( col . db_field_name ) #NEWLINE# deleted_fields = True #NEWLINE# #UNINDENT# else : #NEWLINE# #INDENT# if isinstance ( col , columns . Map ) : #NEWLINE# #INDENT# uc = MapDeleteClause ( col . db_field_name , v . value , v . previous_value ) #NEWLINE# if ( uc . get_context_size ( ) > 0 ) : #NEWLINE# #INDENT# ds . add_field ( uc ) #NEWLINE# deleted_fields = True #NEWLINE# #UNINDENT# #UNINDENT# #UNINDENT# #UNINDENT# if deleted_fields : #NEWLINE# #INDENT# for ( name , col ) in self . model . _primary_keys . items ( ) : #NEWLINE# #INDENT# ds . add_where ( col , EqualsOperator ( ) , getattr ( self . instance , name ) ) #NEWLINE# #UNINDENT# self . _execute ( ds )