Question

One class Customers instantiates many other classes (e.g. CustomersFromMysql, CustomersFromPostgeSQL) that all query databases which give back customer names. Now these customer names come back as for example name = "John Doe", what my Customers class needs though is more than name, it also needs nameNoSpace = "JohnDoe" and nameInvertedComma = "Doe, John" for example.

I would programm a helper class Converter which has methods like invertName(name) and removeComma(name). Would I instantiate the converter in every class that queries the database (CustomersFromMysql, CustomersFromPostgeSQL) to give back all required variables or would I instantiate the Converter in the instantiating class Customers so when I get back results I iterate through my list and batch convert them?

Of course both works, but what is the way to go?

Answer 1

You should remember separation of duties in such cases. The database related classes should handle only the database specific aspects. Performing operations (calculations) on the retrieved data should be treated as business logic. So, if your Customers class already has some logic in it, it would be the perfect place for putting in the conversion routines. Neverthess, it really depends on where you think your logic belongs to.

It may also make sense to apply some naming conventions. In general you can distinguish between at least the different kinds of classes in case like the one you desribed in your question:

1. Data Access Objects (DAO); perform database opertions (your SQL classes)
2. Data Transfer Objects (DTO) or entities; represent the structure of your business objects
3. Business Logic; retrieve the DTO by using DAOs, perform some logic according to your requirements, push the DTO back into the database by using the DAOs again