Subclasses

A powerful of feature of OOP to help remove duplication is subclassing. Subclassing allows you to create inheritance trees to better model your domain.

Entity Structure

We’ll model this example from the following diagram:

app/Domain/Entities/Player.php

<?php

namespace App\Domain\Entities;

use Dms\Core\Model\Object\ClassDefinition;
use Dms\Core\Model\Object\Entity;

abstract class Player extends Entity
{
    const NAME = 'name';
    
    /**
     * @var string
     */
    public $name;

    public function __construct(string $name)
    {
        parent::__construct();
        $this->name = $name;
    }

    /**
     * Defines the structure of this entity.
     *
     * @param ClassDefinition $class
     */
    protected function defineEntity(ClassDefinition $class)
    {
        $class->property($this->name)->asString();
    }
}

app/Domain/Entities/Footballer.php

<?php

namespace App\Domain\Entities;

use Dms\Core\Model\Object\ClassDefinition;

class Footballer extends Player
{
    const CLUB = 'club';
    
    /**
     * @var string
     */
    public $club;

    public function __construct(string $name, string $club)
    {
        parent::__construct($name);
        $this->club = $club;
    }

    /**
     * Defines the structure of this entity.
     *
     * @param ClassDefinition $class
     */
    protected function defineEntity(ClassDefinition $class)
    {
        parent::defineEntity($class);

        $class->property($this->club)->asString();
    }
}

app/Domain/Entities/Cricketer.php

<?php

namespace App\Domain\Entities;

use Dms\Core\Model\Object\ClassDefinition;

class Cricketer extends Player
{
    const BATTING_AVERAGE = 'battingAverage';
    
    /**
     * @var int
     */
    public $battingAverage;

    public function __construct(string $name, int $battingAverage)
    {
        parent::__construct($name);
        $this->battingAverage = $battingAverage;
    }

    /**
     * Defines the structure of this entity.
     *
     * @param ClassDefinition $class
     */
    protected function defineEntity(ClassDefinition $class)
    {
        parent::defineEntity($class);

        $class->property($this->battingAverage)->asInt();
    }
}

app/Domain/Entities/Bowler.php

<?php

namespace App\Domain\Entities;

use Dms\Core\Model\Object\ClassDefinition;

class Bowler extends Cricketer
{
    const BOWLING_AVERAIGE = 'bowlingAverage';
    
    /**
     * @var int
     */
    public $bowlingAverage;

    public function __construct(string $name, int $battingAverage, int $bowlingAverage)
    {
        parent::__construct($name, $battingAverage);
        $this->bowlingAverage = $bowlingAverage;
    }

    /**
     * Defines the structure of this entity.
     *
     * @param ClassDefinition $class
     */
    protected function defineEntity(ClassDefinition $class)
    {
        parent::defineEntity($class);

        $class->property($this->bowlingAverage)->asInt();
    }
}

Mapper Configuration (Single Table Inheritance)

You can map all the subclasses to one database table using single table inheritance pattern with a type column.

<?php declare(strict_types=1);

namespace App\Infrastructure\Persistence;

use App\Domain\Entities\Bowler;
use App\Domain\Entities\Cricketer;
use App\Domain\Entities\Footballer;
use App\Domain\Entities\Player;
use Dms\Core\Persistence\Db\Mapping\Definition\MapperDefinition;
use Dms\Core\Persistence\Db\Mapping\EntityMapper;

/**
 * @author Elliot Levin <elliotlevin@hotmail.com>
 */
class PlayerMapper extends EntityMapper
{
    /**
     * Defines the entity mapper
     *
     * @param MapperDefinition $map
     *
     * @return void
     */
    protected function define(MapperDefinition $map)
    {
        $map->type(Player::class);
        $map->toTable('players');

        $map->idToPrimaryKey('id');

        $map->column('type')->asEnum(['footballer', 'cricketer', 'bowler']);
        $map->property(Player::NAME)->to('name')->asVarchar(255);

        $map->subclass()->withTypeInColumn('type', 'footballer')->define(function (MapperDefinition $map) {
            $map->type(Footballer::class);
            $map->property(Footballer::CLUB)->to('club')->asVarchar(255);
        });

        $map->subclass()->withTypeInColumn('type', 'cricketer')->define(function (MapperDefinition $map) {
            $map->type(Cricketer::class);
            $map->property(Cricketer::BATTING_AVERAGE)->to('batting_average')->asInt();

            $map->subclass()->withTypeInColumn('type', 'bowler')->define(function (MapperDefinition $map) {
                $map->type(Bowler::class);
                $map->property(Bowler::BOWLING_AVERAGE)->to('bowling_average')->asInt();
            });
        });
    }
}

Mapper Configuration (Class Table Inheritance)

Alternatively, you can map each the subclasses to a separate table.

<?php declare(strict_types=1);

namespace App\Infrastructure\Persistence;

use App\Domain\Entities\Bowler;
use App\Domain\Entities\Cricketer;
use App\Domain\Entities\Footballer;
use App\Domain\Entities\Player;
use Dms\Core\Persistence\Db\Mapping\Definition\MapperDefinition;
use Dms\Core\Persistence\Db\Mapping\EntityMapper;

/**
 * @author Elliot Levin <elliotlevin@hotmail.com>
 */
class PlayerMapper extends EntityMapper
{
    /**
     * Defines the entity mapper
     *
     * @param MapperDefinition $map
     *
     * @return void
     */
    protected function define(MapperDefinition $map)
    {
        $map->type(Player::class);
        $map->toTable('players');

        $map->idToPrimaryKey('id');
        $map->property(Player::NAME)->to('name')->asVarchar(255);

        $map->subclass()->asSeparateTable('footballers')->define(function (MapperDefinition $map) {
            $map->type(Footballer::class);
            $map->property(Footballer::CLUB)->to('club')->asVarchar(255);
        });

        $map->subclass()->asSeparateTable('cricketers')->define(function (MapperDefinition $map) {
            $map->type(Cricketer::class);
            $map->property(Cricketer::BATTING_AVERAGE)->to('batting_average')->asInt();

            $map->subclass()->asSeparateTable('bowlers')->define(function (MapperDefinition $map) {
                $map->type(Bowler::class);
                $map->property(Bowler::BOWLING_AVERAGE)->to('bowling_average')->asInt();
            });
        });
    }
}

Module Configuration

Modules support mapping to entity subclasses as shown in the following example

<?php declare(strict_types=1);

namespace App\Cms\Modules;

use App\Domain\Entities\Bowler;
use App\Domain\Entities\Cricketer;
use App\Domain\Entities\Footballer;
use App\Domain\Entities\Player;
use Dms\Common\Structure\Field;
use Dms\Core\Auth\IAuthSystem;
use Dms\Core\Common\Crud\CrudModule;
use Dms\Core\Common\Crud\Definition\CrudModuleDefinition;
use Dms\Core\Common\Crud\Definition\Form\CrudFormDefinition;
use Dms\Core\Common\Crud\Definition\Table\SummaryTableDefinition;

/**
 * The player module.
 */
class PlayerModule extends CrudModule
{
    /**
     * Defines the structure of this module.
     *
     * @param CrudModuleDefinition $module
     */
    protected function defineCrudModule(CrudModuleDefinition $module)
    {
        $module->name('player');

        $module->labelObjects()->fromProperty(Player::NAME);

        $module->crudForm(function (CrudFormDefinition $form) {
            $typeField = Field::create('type', 'Type')->string()->oneOf([
                'footballer' => 'Footballer',
                'cricketer'  => 'Cricketer',
                'bowler'     => 'Bowler',
            ]);

            if (!$form->isCreateForm()) {
                // If the entity is already exist the type of the entity cannot be changed
                $typeField->readonly();
            }

            $form->section('Details', [
                $form->field(
                    Field::create('name', 'Name')->string()->required()
                )->bindToProperty(Player::NAME),
                //
                $form->field(
                    $typeField
                )->bindToCallbacks(function (Player $player) {
                    return [
                           Footballer::class => 'footballer',
                           Cricketer::class  => 'cricketer',
                           Bowler::class     => 'bowler',
                       ][get_class($player)];
                }, function () {
                    // Unused
                }),
            ]);

            $form->dependentOn(['type'], function (CrudFormDefinition $form, array $input) {
                if ($input['type'] === 'footballer') {
                    $form->mapToSubClass(Footballer::class);

                    $form->continueSection([
                        $form->field(
                            Field::create('club', 'Club')->string()->required()
                        )->bindToProperty(Footballer::CLUB)
                    ]);
                }

                if ($input['type'] === 'cricketer' || $input['type'] === 'bowler') {
                    if ($input['type'] === 'cricketer') {
                        $form->mapToSubClass(Cricketer::class);
                    }

                    $form->continueSection([
                        $form->field(
                            Field::create('batting_average', 'Batting Average')->int()->required()
                        )->bindToProperty(Cricketer::BATTING_AVERAGE)
                    ]);

                    if ($input['type'] === 'bowler') {
                        $form->mapToSubClass(Bowler::class);

                        $form->continueSection([
                            $form->field(
                                Field::create('bowling_average', 'Bowling Average')->int()->required()
                            )->bindToProperty(Bowler::BOWLING_AVERAGE)
                        ]);
                    }
                }
            });
        });

        $module->removeAction()->deleteFromDataSource();

        $module->summaryTable(function (SummaryTableDefinition $table) {
            $table->mapProperty(Player::NAME)->to(Field::create('name', 'Name')->string());

            $table->view('all', 'All')
                ->loadAll()
                ->asDefault();
        });
    }
}