zero to solid

Zero to SOLIDin 45 Minutes

by Vic Metcalfe@v_metcalfe

I made an e-Commercesite in PHP!

Children or those feint of heart are warned to

leave the room…

<?phpsession_start();$connection = new \PDO('mysql:host=localhost;dbname=solid', 'root', '');if (!isset($_SESSION['cart'])) { $connection->exec("INSERT INTO cart () VALUES ()"); $_SESSION['cart'] = $connection->lastInsertId();}

if (isset($_POST['addproduct'])) { $sql = "INSERT INTO cartitem (cart, product, quantity) VALUES (:cart, :product, :quantity) ON DUPLICATE KEY UPDATE quantity = quantity + :quantity"; $parameters = [ 'cart' => $_SESSION['cart'], 'product' => $_POST['addproduct'], 'quantity' => $_POST['quantity'], ]; $statement = $connection->prepare($sql); $statement->execute($parameters);}

if (isset($_POST['update'])) { $sql = "UPDATE cartitem SET quantity=:quantity WHERE cart=:cart and product=:product"; $parameters = [ 'cart' => $_SESSION['cart'], 'product' => $_POST['update'], 'quantity' => $_POST['quantity'], ]; $statement = $connection->prepare($sql); $statement->execute($parameters);}

https://github.com/zymsys/solid/blob/00/cart.php

$statement = $connection->prepare("SELECT * FROM cartitem WHERE cart=:cart AND quantity <> 0");$statement->execute(['cart' => $_SESSION['cart']]);$cartItems = $statement->fetchAll();?><!doctype html><html lang="en"><head> <meta charset="UTF-8"> <title>GTA-PHP Gift Shop</title> <link rel="stylesheet" href="site.css"></head><body><div class="container"> <h1>GTA-PHP Gift Shop</h1> <p>Buy our junk to keep our organizers up to date with the latest gadgets.</p> <table class="table"> <tr> <th>Product Name</th> <th>You Pay</th> <th>Group Gets</th> <th></th> </tr> <?php $products = []; $result = $connection->query("SELECT * FROM product"); foreach ($result as $product) { $products[$product['id']] = $product; ?> <tr> <td><?php echo $product['name']; ?></td>

<td><?php $price = $product['price']; echo number_format($price / 100, 2); ?></td> <td> <?php echo number_format( ($product['price'] - $product['cost']) / 100, 2 ); ?> </td> <td> <form method="post"> <input type="number" name="quantity" value="1" style="width: 3em"> <input type="hidden" name="addproduct" value="<?php echo $product['id']; ?>"> <input class="btn btn-default btn-xs" type="submit" value="Add to Cart"> </form> </td> </tr> <?php } ?> </table> <?php if (count($cartItems) > 0): ?> <?php $total = 0; $taxable = 0;

$provinceCode = isset($_GET['province']) ? $_GET['province'] : 'ON'; //Default to GTA-PHP's home $provinces = [];


$result = $connection->query("SELECT * FROM province ORDER BY name"); foreach ($result as $row) { $provinces[$row['code']] = $row; if ($row['code'] === $provinceCode) { $province = $row; } } ?> <h2>Your Cart:</h2> <table class="table"> <?php foreach ($cartItems as $cartItem): ?> <?php $product = $products[$cartItem['product']]; ?> <tr> <td> <?php echo $product['name']; ?> </td> <td> <form method="post"> Quantity: <input type="hidden" name="update" value="<?php echo $product['id']; ?>"> <input type="number" name="quantity" style="width: 3em" value="<?php echo $cartItem['quantity']; ?>"> <button type="submit">Update</button> </form> </td> <td> <?php echo number_format( $cartItem['quantity'] * $product['price'] / 100, 2 ); $itemTotal = $cartItem['quantity'] * $product['price'];


$total += $itemTotal; $taxable += $product['taxes'] ? $itemTotal : 0; ?> </td> </tr> <?php endforeach; ?> <tr> <td></td> <td style="text-align: right">Subtotal:</td> <td><?php echo number_format($total / 100, 2); ?></td> </tr> <tr> <td></td> <td style="text-align: right"> <?php echo $province['name']; ?> taxes at <?php echo $province['taxrate'] ?>%:</td> <td> <?php $taxes = $taxable * $province['taxrate'] / 100; $total += $taxes; echo number_format($taxes / 100, 2); ?> </td> </tr> <tr> <td></td> <td style="text-align: right">Total:</td> <td><?php echo number_format($total / 100, 2); ?></td> </tr> </table> <form method="get"> Calculate taxes for purchase from: <select name="province">

<?php foreach ($provinces as $province): ?> <?php $selected = $provinceCode === $province['code'] ? 'selected' : ''; ?> <option value="<?php echo $province['code']; ?>" <?php echo $selected; ?>> <?php echo $province['name']; ?> </option> <?php endforeach; ?> </select> <button type="submit" class="btn btn-default btn-xs"> Recalculate</button> </form> <form action="checkout.php" method="post"> <?php foreach ($cartItems as $itemNumber => $cartItem): ?> <?php $product = $products[$cartItem['product']]; ?> <input type="hidden" name="item<?php echo $itemNumber; ?>" value="<?php echo $product['name'] . '|' . number_format($product['price'] / 100, 2); ?>"> <?php endforeach; ?> <input type="hidden" name="item<?php echo count($cartItems); ?>" value="<?php echo 'Tax|' . number_format($taxes / 100, 2); ?>"> <button type="submit" class="btn btn-primary" style="float: right"> Checkout </button> </form> <?php endif; ?></div></body></html>


Is there anything wrong with this?

Step 1:Separate PHP from

HTML

<?phpfunction initialize(){ global $connection;

session_start(); $connection = new \PDO('mysql:host=localhost;dbname=solid', 'root', ''); if (!isset($_SESSION['cart'])) { $connection->exec("INSERT INTO cart () VALUES ()"); $_SESSION['cart'] = $connection->lastInsertId(); }}

function handleAdd(){ global $connection;

if (!isset($_POST['addproduct'])) { return; } $sql = "INSERT INTO cartitem (cart, product, quantity) VALUES (:cart, :product, :quantity) ON DUPLICATE KEY UPDATE quantity = quantity + :quantity"; $parameters = [ 'cart' => $_SESSION['cart'], 'product' => $_POST['addproduct'], 'quantity' => $_POST['quantity'], ]; $statement = $connection->prepare($sql); $statement->execute($parameters);}



<!doctype html><html lang="en"><head> <meta charset="UTF-8"> <title>GTA-PHP Gift Shop</title> <link rel="stylesheet" href="site.css"></head><body><div class="container"> <h1>GTA-PHP Gift Shop</h1> <p>Buy our junk to keep our organizers up to date with the latest gadgets.</p> <table class="table"> <tr> <th>Product Name</th> <th>You Pay</th> <th>Group Gets</th> <th></th> </tr> <?php foreach ($viewData['products'] as $product): ?> <tr> <td><?php echo $product['name']; ?></td> <td><?php $price = $product['price']; echo number_format($price / 100, 2); ?></td> <td><?php echo number_format( ($product['price'] - $product['cost']) / 100, 2 ); ?></td>

<td> <form method="post"> <input type="number" name="quantity" value="1" style="width: 3em"> <input type="hidden" name="addproduct" value="<?php echo $product['id']; ?>"> <input class="btn btn-default btn-xs" type="submit" value="Add to Cart"> </form> </td> </tr> <?php endforeach; ?> </table> <?php if (count($viewData['cartItems']) > 0): ?> <h2>Your Cart:</h2> <table class="table"> <?php foreach ($viewData['cartItems'] as $cartItem): ?> <?php $product = $viewData['products'][$cartItem['product']]; ?> <tr> <td> <?php echo $product['name']; ?> </td> <td> <form method="post"> Quantity: <input type="hidden" name="update" value="<?php echo $product['id']; ?>"> <input type="number" name="quantity" style="width: 3em" value="<?php echo $cartItem['quantity']; ?>"> <button type="submit">Update</button> </form> </td>



<td> <?php echo number_format( $cartItem['quantity'] * $product['price'] / 100, 2 ); ?> </td> </tr> <?php endforeach; ?> <tr> <td></td> <td style="text-align: right">Subtotal:</td> <td><?php echo number_format($viewData['subtotal'] / 100, 2); ?></td> </tr> <tr> <td></td> <td style="text-align: right"> <?php echo $viewData['province']['name']; ?> taxes at <?php echo $viewData['province']['taxrate'] ?>%:</td> <td> <?php echo number_format($viewData['taxes'] / 100, 2); ?> </td> </tr> <tr> <td></td> <td style="text-align: right">Total:</td> <td><?php echo number_format($viewData['total'] / 100, 2); ?></td> </tr> </table>

<form method="get"> Calculate taxes for purchase from: <select name="province"> <?php foreach ($viewData['provinces'] as $province): ?> <?php $selected = $viewData['provinceCode'] === $province['code'] ? 'selected' : ''; ?> <option value="<?php echo $province['code']; ?>" <?php echo $selected; ?>> <?php echo $province['name']; ?> </option> <?php endforeach; ?> </select> <button type="submit" class="btn btn-default btn-xs">Recalculate</button> </form> <form action="checkout.php" method="post"> <?php foreach ($viewData['cartItems'] as $itemNumber => $cartItem): ?> <?php $product = $viewData['products'][$cartItem['product']]; ?> <input type="hidden" name="item<?php echo $itemNumber; ?>" value="<?php echo $product['name'] . '|' . number_format($product['price'] / 100, 2); ?>"> <?php endforeach; ?>



<input type="hidden" name="item<?php echo count($viewData['cartItems']); ?>" value="<?php echo 'Tax|' . number_format($viewData['taxes'] / 100, 2); ?>"> <button type="submit" class="btn btn-primary" style="float: right"> Checkout</button> </form> <?php endif; ?></div></body></html>



Any room for improvement now?

ObjectsA very brief introduction

Objects help us to organize our code

function initialize()function handleAdd()function handleUpdate()function loadCartItems()function loadProducts()function loadProvinces()

function calculateCartSubtotal($cartItems, $products)function calculateCartTaxes($cartItems, $products, $taxrate)

function buildViewData()

How might we group these functions?

function initialize()function handleAdd()function handleUpdate()

function loadCartItems()function loadProducts()function loadProvinces()



Invisible stuff that happens on page load

Loads stuff into our HTML

(view)

Objects help us to encapsulate code







(view)

function initialize()

function handleAdd()function handleUpdate()




private private

public

private private

public

private private private

class Initializer{ private $connection;

public function __construct(\PDO $connection) { $this->connection = $connection; }

public function initialize() { session_start(); if (!isset($_SESSION['cart'])) { $this->connection->exec("INSERT INTO cart () VALUES ()"); $_SESSION['cart'] = $this->connection->lastInsertId(); } $this->handleAdd(); $this->handleUpdate(); }

private function handleAdd() { … } private function handleUpdate() { … }}



class ViewData { private $connection;


private function loadCartItems() { … } private function loadProducts(){ … } private function loadProvinces(){ … } private function calculateCartSubtotal($cartItems, $products) { … } private function calculateCartTaxes($cartItems, $products, $taxrate) { … } public function buildViewData() { … }}



public function buildViewData(){ $viewData = [ 'cartItems' => $this->loadCartItems(), 'products' => $this->loadProducts(), 'provinces' => $this->loadProvinces(), 'provinceCode' => isset($_GET['province']) ? $_GET['province'] : 'ON', //Default to GTA-PHP's home ];


$viewData['subtotal'] = $this->calculateCartSubtotal($viewData['cartItems'], $viewData['products']); $viewData['taxes'] = $this->calculateCartTaxes($viewData['cartItems'], $viewData['products'], $viewData['province']['taxrate']); $viewData['total'] = $viewData['subtotal'] + $viewData['taxes'];

return $viewData;}



SOLIDFewer Gremlins in your Code

SRPSingle Responsibility Principal

Responsibility?

Business Responsibility

not code







(view)

function initialize()

function handleAdd()function handleUpdate()function loadCartItems()

function loadProducts()

function loadProvinces()



Sales

Accounting

Inventory

Application / IT

class Application{ private $connection;

public function __construct() { $this->connection = new \PDO('mysql:host=localhost;dbname=solid', 'root', ''); $this->inventory = new Inventory($this->connection); $this->sales = new Sales($this->connection); $this->accounting = new Accounting($this->connection); }

public function initialize() { session_start(); if (!isset($_SESSION['cart'])) { $this->connection->exec("INSERT INTO cart VALUES ()"); $_SESSION['cart'] = $this->connection->lastInsertId(); } $this->handlePost(); }



public function buildViewData() { $viewData = [ 'cartItems' => $this->sales->loadCartItems(), 'products' => $this->inventory->loadProducts(), 'provinces' => $this->accounting->loadProvinces(), 'provinceCode' => isset($_GET['province']) ? $_GET['province'] : 'ON', //Default to GTA-PHP's home ];


$viewData['subtotal'] = $this->accounting-> calculateCartSubtotal($viewData['cartItems'], $viewData['products']); $viewData['taxes'] = $this->accounting-> calculateCartTaxes($viewData['cartItems'], $viewData['products'], $viewData['province']['taxrate']); $viewData['total'] = $viewData['subtotal'] + $viewData['taxes'];

return $viewData; }

//Class Application Continued…



private function handlePost() { if (isset($_POST['addproduct'])) { $this->sales->addProductToCart( $_SESSION['cart'], $_POST['addproduct'], $_POST['quantity'] ); } if (isset($_POST['update'])) { $this->sales->modifyProductQuantityInCart( $_SESSION['cart'], $_POST['update'], $_POST['quantity'] ); } }}

//Class Application Continued…



class Inventory { private $connection;


public function loadProducts() { $products = []; $result = $this->connection->query("SELECT * FROM product"); foreach ($result as $product) { $products[$product['id']] = $product; } return $products; }}



class Sales { private $connection;


public function addProductToCart($cartId, $productId, $quantity) { $sql = "INSERT INTO cartitem (cart, product, quantity) VALUES (:cart, :product, :quantity) ON DUPLICATE KEY UPDATE quantity = quantity + :quantity"; $parameters = [ 'cart' => $cartId, 'product' => $productId, 'quantity' => $quantity, ]; $statement = $this->connection->prepare($sql); $statement->execute($parameters); }



public function modifyProductQuantityInCart($cartId, $productId, $quantity) { $sql = "UPDATE cartitem SET quantity=:quantity WHERE cart=:cart and product=:product"; $parameters = [ 'cart' => $cartId, 'product' => $productId, 'quantity' => $quantity, ]; $statement = $this->connection->prepare($sql); $statement->execute($parameters); }

public function loadCartItems() { $statement = $this->connection->prepare("SELECT * FROM cartitem WHERE cart=:cart AND quantity <> 0"); $statement->execute(['cart' => $_SESSION['cart']]); return $statement->fetchAll(); }}

//Class Sales Continued…



class Accounting { private $connection;


public function loadProvinces() { $provinces = []; $result = $this->connection->query("SELECT * FROM province ORDER BY name"); foreach ($result as $row) { $provinces[$row['code']] = $row; } return $provinces; }

public function calculateCartSubtotal($cartItems, $products) { $subtotal = 0;

foreach ($cartItems as $cartItem) { $product = $products[$cartItem['product']]; $subtotal += $cartItem['quantity'] * $product['price']; }

return $subtotal; }



public function calculateCartTaxes($cartItems, $products, $taxrate) { $taxable = 0;

foreach ($cartItems as $cartItem) { $product = $products[$cartItem['product']]; $taxable += $product['taxes'] ? $cartItem['quantity'] * $product['price'] : 0; } return $taxable * $taxrate / 100; }

}

//Class Accounting Continued…



OCPOpen/Closed Principle

Open and Closed?

Open to Extension

Closed to Modification

New requirement:10% off orders over

$100

Where does the code go?

First we need to understand

inheritance and polymorphism

Classes can extend other classes

class AccountingStrategy { private $description;

public function __construct($description) { $this->description = $description; }

public function getAdjustment($cartItems) { return false; }

public function getDescription() { return $this->description; }}



class TaxAccountingStrategy extends AccountingStrategy { private $products; private $taxRate;

public function __construct($products, $province) { parent::__construct($province['name'] . ' taxes at ' . $province['taxrate'] . '%:'); $this->products = $products; $this->taxRate = $province['taxrate']; }

public function getAdjustment($cartItems) { $taxable = 0;

foreach ($cartItems as $cartItem) { $product = $this->products[$cartItem['product']]; $taxable += $product['taxes'] ? $cartItem['quantity'] * $product['price'] : 0; } return $taxable * $this->taxRate / 100; }}



TaxAccountingStrategy is an

AccountingStrategy.

public function initialize(){ session_start(); if (!isset($_SESSION['cart'])) { $this->connection->exec("INSERT INTO cart VALUES ()"); $_SESSION['cart'] = $this->connection->lastInsertId(); } $this->handlePost();

$this->products = $this->inventory->loadProducts(); $provinceRepository = new ProvinceRepository($this->connection, isset($_GET['province']) ? $_GET['province'] : 'ON'); $this->provinces = $provinceRepository->loadProvinces(); $this->selectedProvince = $provinceRepository->getSelectedProvince();

$this->accounting->addStrategy( new TaxAccountingStrategy( $this->products, $provinceRepository->getSelectedProvince() ) );}

public function initialize(){ session_start(); if (!isset($_SESSION['cart'])) { $this->connection->exec("INSERT INTO cart VALUES ()"); $_SESSION['cart'] = $this->connection->lastInsertId(); } $this->handlePost();}



public function buildViewData(){ $viewData = [ 'cartItems' => $this->sales->loadCartItems(), 'products' => $this->inventory->loadProducts(), 'provinces' => $this->accounting->loadProvinces(), 'provinceCode' => isset($_GET['province']) ? $_GET['province'] : 'ON', //Default to GTA-PHP's home ];

public function buildViewData(){ $cartItems = $this->sales->loadCartItems(); $viewData = [ 'cartItems' => $cartItems, 'products' => $this->products, 'provinces' => $this->provinces, 'adjustments' => $this->accounting->applyAdjustments($cartItems), 'provinceCode' => $this->selectedProvince['code'], ];

Done in initialize()

now

Used Twice

New!

Start of buildViewData()



End of buildViewData()

$viewData['subtotal'] = $this->accounting-> calculateCartSubtotal($viewData['cartItems'], $viewData['products']); $viewData['taxes'] = $this->accounting-> calculateCartTaxes($viewData['cartItems'], $viewData['products'], $viewData['province']['taxrate']); $viewData['total'] = $viewData['subtotal'] + $viewData['taxes'];

return $viewData;}

$viewData['subtotal'] = $this->accounting-> calculateCartSubtotal($viewData['cartItems'], $viewData['products']); $viewData['total'] = $viewData['subtotal'] + $this->accounting->getAppliedAdjustmentsTotal();

return $viewData;}

Taxes are handled by adjustmentsand removed as a specific item in

the view’s data.



// loadProvinces used to live in the Accounting classclass ProvinceRepository{ private $connection; private $provinces = null; private $selectedProvince; private $selectedProvinceCode;

public function __construct(\PDO $connection, $selectedProvinceCode) { $this->connection = $connection; $this->selectedProvinceCode = $selectedProvinceCode; }

public function loadProvinces() { … } // Now sets $selectedProvince

public function getProvinces() { return is_null($this->provinces) ? $this->loadProvinces() : $this->provinces; }

public function getSelectedProvince() { return $this->selectedProvince; }}



Remove calculateCartTaxes and add AccountingStrategy

class Accounting { private $connection; private $strategies = []; private $appliedAdjustments = 0;


public function calculateCartSubtotal($cartItems, $products) { … } // No change

public function addStrategy(AccountingStrategy $strategy) { $this->strategies[] = $strategy; }



public function applyAdjustments($cartItems) { $adjustments = []; foreach ($this->strategies as $strategy) { $adjustment = $strategy->getAdjustment($cartItems); if ($adjustment) { $this->appliedAdjustments += $adjustment; $adjustments[] = [ 'description' => $strategy->getDescription(), 'adjustment' => $adjustment, ]; } } return $adjustments; }

public function getAppliedAdjustmentsTotal() { return $this->appliedAdjustments; }}

//Class Accounting Continued…



<?php foreach ($viewData['adjustments'] as $adjustment): ?><tr> <td></td> <td style="text-align: right"> <?php echo $adjustment['description']; ?> </td> <td> <?php echo number_format($adjustment['adjustment'] / 100, 2); ?> </td></tr><?php endforeach; ?>

<?phpfor ($adjustmentIndex = 0; $adjustmentIndex < count($viewData['adjustments']); $adjustmentIndex += 1): $adjustment = $viewData['adjustments'][$adjustmentIndex];?><input type="hidden" name="item<?php echo $adjustmentIndex; ?>" value="<?php echo $adjustment['description'] . '|' . number_format($adjustment['adjustment'] / 100, 2); ?>"><?php endfor; ?>

Now we can add DiscountAccountingStrategy

without modifying Accounting or the view

class DiscountAccountingStrategy extends AccountingStrategy { private $products;

public function __construct($products) { parent::__construct("Discount for orders over $100"); $this->products = $products; }

public function getAdjustment($cartItems) { $total = array_reduce($cartItems, function ($carry, $item) { $product = $this->products[$item['product']]; return $carry + $item['quantity'] * $product['price']; }, 0); return $total > 10000 ? ($total / -10) : false; }}



In Application::initialize(

)$this->accounting->addStrategy( new DiscountAccountingStrategy($this->products));



LSPLiskov Substitution Principal

If a class is a thing, it should act like that

thing. must

Square is a Rectangle?

Ways to break LSP• Throw a new exception• Add requirements to parameters

• requiring a more specific type• Return an unexpected type

• returning a less specific type• Do anything that would be unexpected if

used as a stand-in for an ancestor

DIPDependency Inversion Principle

Yeah smarty-pants, the D does come

before the I

Classes can implement interfaces,

and can depend on interfaces

Our Dependencies

Dependency Inversion

We can scrap the AccountingStrategy class and

add…interface AccountingStrategyInterface{ public function getDescription(); public function getAdjustment($cartItems);}



Because Application creates concrete classes there’s little to be gained by

adding other interfacespublic function __construct(){ $this->connection = new \PDO('mysql:host=localhost;dbname=solid', 'root', ''); $this->inventory = new Inventory($this->connection); $this->sales = new Sales($this->connection); $this->accounting = new Accounting($this->connection);}

Dependency Injection Containers would solve this, but are a topic for

another talk.



ISPInterface Segregation Principal

If we follow SRP and interfaces describe

classes, what’s left to segregate?

Code Responsibilities

Imagine an interface to our Sales class

interface SalesInterface{

public function addProductToCart($cartId, $productId, $quantity); public function modifyProductQuantityInCart($cartId, $productId, $quantity);

public function loadCartItems();}

Imagine an interface to our Sales class

interface SalesWriterInterface{

public function addProductToCart($cartId, $productId, $quantity); public function modifyProductQuantityInCart($cartId, $productId, $quantity);

public function loadCartItems();

}

interface SalesReaderInterface{

}

Last words

Resist OverengineeringSimplify don’t complicate

Pragmatic not Dogmatic

Questions?

zero to solid

Technology