'Add values to a new field according to the mappings given through the mapping_function
@param tablename        : name of the original table in which the new unique field id added
@param field_to_update  : name of the field to be updated according to the mapping
@param mapping_function : class instance containing the mapping functions
@param list_of_tables   : list of tables which the table references'

def migrate_to_unique_field(self, tablename, field_to_update, mapping_function, list_of_tables=None):

    db = self.db
    self._add_new_fields(db, field_to_update, tablename)
    self._add_tables_temp_db(db, list_of_tables)
    self.update_field_by_mapping(db, tablename, field_to_update, mapping_function)
