I have a class for creating objects from a database row. How to design a class to perform functions on all rows e.g. counts on db table

Question

Say I have a database for storing cars data. Each row is essentially a car and I've a class that takes a row of the data and builds my car object.

I now want to build a dashboard that can tell me all the types of cars e.g.

Type Amount
BMW 12
Ford 7

I'm trying to figure out how best to design the functionality. My thoughts so far have been:

• Static function call in a generic functions class. Does a count on the table. Not exactly an OOP approach so I'd prefer not to do this.

• Create a class for counting cars. Not sure if this is too specific a case to warrant it's own class.

• A database interface class for cars table. Perform general functions, counts, bulk updates etc. Should be static?

• A counter interface class? I'm not too clear on how to build this, it's something I've kind of gleaned from reading about interfaces and decoupling?

Those are the thoughts I had. What are the suggested ways to handle this?

Answer 1

There are several ways to achieve your goal. Which you are going to use depends on your preferences and whether you are having an underlaying framework or CMS which uses a certain way. In case you are using a framework or similiar check their coding guidelines.

Despite that I am aware of following options:

• DBAL that provides functions like count($table).
• Model that provides functions like count. Further the model provides functions like get(id) and set(...$args)
• A RepositoryClass that supports CRUD for it's model and general methods used to interact with the database. For each Model you have a RepositoryClass.
• A ListClass that you can use with count(). Similiar to RepositoryClass. However, the ListClass contains actually a list while the RepositoryClass returns objects or e.g. the amount of cars in your database.

I prefer the usage of either a ListClass and or RepositoryClass. In the following example we have a CarRepository having a method to retrieve every available brand. The method findCarBrands returns the class CarBrandList which contains a list with models of type CarBrand. As it is a list we can iterate through it and access each brand. The CarBrand-Model has a method to get the total amount of available cars per brand. You may ask yourself where is the returned value of getTotalCars determined. This is done in the repository class when we iterate through the sql resultSet or in the sql statement itself.

<?php
 /** @var CarBrandList $carBrands*/
 $carBrands = $carRepository->findCarBrands();
 /** @var CarBrand $carBrand*/
 foreach ($carBrands as $carBrand)
 {
 echo $carBrand->getName() . ' | ' . $carBrand()->getTotalCars() . '<br/>';
 }