Defining a mapper

A mapper or data mapper works in much the same manner as a hydrator: converting data from one model, be it array or object, into another. A critical difference is that the hydrator is generic and does not need to have object property names pre-programmed, whereas the mapper is the opposite: it needs precise information on property names for both models. In this recipe we will demonstrate the use of a mapper to convert data from one database table into another.

How to do it...

1. We first define a Application\Database\Mapper\FieldConfig class, which contains mapping instructions for individual fields. We also define appropriate class constants:

   namespace Application\Database\Mapper;
   use InvalidArgumentException;
   class FieldConfig
   {
     const ERROR_SOURCE = 
       'ERROR: need to specify destTable and/or source';
     const ERROR_DEST   = 'ERROR: need to specify either '
       . 'both destTable and destCol or neither';

2. Key properties are defined along with the appropriate class constants...