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06.

Fetching Objects from the Database

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Getting our Ship objects is easy: create a ShipLoader and call getShips() on it. We don't care how ShipLoader is getting these - that's its problem.

Hardcoding is so 1990, let's load objects from the database! We need to get these ships to their battlestations!

Database Setup

At the root of your project, open up a resources directory. Copy init_db.php out of there to the root of your project and open it up:

57 lines | init_db.php
<?php
/*
* SETTINGS!
*/
$databaseName = 'oo_battle';
$databaseUser = 'root';
$databasePassword = '';
/*
* CREATE THE DATABASE
*/
$pdoDatabase = new PDO('mysql:host=localhost', $databaseUser, $databasePassword);
$pdoDatabase->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$pdoDatabase->exec('CREATE DATABASE IF NOT EXISTS oo_battle');
// ... lines 16 - 57

Tip

In order for this to work, make sure that you have MySQL installed and running on your machine. There are various ways to install MySQL in different environments - if you have any questions, let us know in the comments!

This script will create a database and add a ship table with columns for id, name, weapon_power, jedi_factor, strength and is_under_repair:

57 lines | init_db.php
// ... lines 1 - 25
$pdo->exec('CREATE TABLE `ship` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(255) COLLATE utf8mb4_unicode_ci NOT NULL,
`weapon_power` int(4) NOT NULL,
`jedi_factor` int(4) NOT NULL,
`strength` int(4) NOT NULL,
`is_under_repair` tinyint(1) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci');
// ... lines 35 - 57

At the bottom, it inserts 4 rows into that table for the 4 ships we have hardcoded right now:

57 lines | init_db.php
// ... lines 1 - 38
$pdo->exec('INSERT INTO ship
(name, weapon_power, jedi_factor, strength, is_under_repair) VALUES
("Jedi Starfighter", 5, 15, 30, 0)'
);
$pdo->exec('INSERT INTO ship
(name, weapon_power, jedi_factor, strength, is_under_repair) VALUES
("CloakShape Fighter", 2, 2, 70, 0)'
);
$pdo->exec('INSERT INTO ship
(name, weapon_power, jedi_factor, strength, is_under_repair) VALUES
("Super Star Destroyer", 70, 0, 500, 0)'
);
$pdo->exec('INSERT INTO ship
(name, weapon_power, jedi_factor, strength, is_under_repair) VALUES
("RZ-1 A-wing interceptor", 4, 4, 50, 0)'
);
// ... lines 55 - 57

If we run this file, it should get everything powered up. Head to your browser and run it there:

http://localhost:8000/init_db.php

If you see - Ding! - you know it worked. If you see a terrible error, check the database credentials at the top - make sure the user can create a new database.

If you want to check the database with something like phpMyAdmin, you'll see one ship table with 4 rows.

Querying for Ships

You look ready to query, copy the two lines that create the PDO object in init_db and head into ShipLoader. Keep things simple: getShips() needs to make a query. So for now, paste the PDO lines right here. Update the database name to be oo_battle and I'll fill in root as the user with no password:

44 lines | lib/ShipLoader.php
// ... lines 1 - 2
class ShipLoader
{
public function getShips()
{
$pdo = new PDO('mysql:host=localhost;dbname=oo_battle', 'root');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
// ... lines 9 - 41
}
}

Ok, query time! Create a $statement variable and set it to $pdo->prepare() with the query inside - SELECT * FROM ship:

44 lines | lib/ShipLoader.php
// ... lines 1 - 4
public function getShips()
{
$pdo = new PDO('mysql:host=localhost;dbname=oo_battle', 'root');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$statement = $pdo->prepare('SELECT * FROM ship');
// ... lines 10 - 41
}
// ... lines 43 - 44

If PDO or prepared statements are new to you, don't worry - they're pretty easy. And besides, using PDO is another chance to play with objects!

Run $statement->execute() to send the query into hyperdrive and create a new $shipsArray that's set to $statement->fetchAll() with an argument: PDO::FETCH_ASSOC. var_dump this variable:

44 lines | lib/ShipLoader.php
// ... lines 1 - 4
public function getShips()
{
$pdo = new PDO('mysql:host=localhost;dbname=oo_battle', 'root');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$statement = $pdo->prepare('SELECT * FROM ship');
$statement->execute();
$shipsArray = $statement->fetchAll(PDO::FETCH_ASSOC);
var_dump($shipsArray);die;
// ... lines 13 - 41
}
// ... lines 43 - 44

This queries for every row and returns an associative array. The PDO::FETCH_ASSOC part is a class constant - a nice little feature of classes we'll talk about later.

Let's see what this looks like! Head back to the homepage and refresh! AND... I was not expecting an error: "Unknown database oo_battles". The database should be called oo_battle - silly me! Refresh again!

Ok! 4 rows of data.

Private Functions are Awesome

Of course, what we need are objects, not arrays. But first, a quick piece of organization. Copy all this good PDO stuff and at the bottom, create a new private function queryForShips(). Paste here and return that $shipsArray:

50 lines | lib/ShipLoader.php
// ... lines 1 - 2
class ShipLoader
{
// ... lines 5 - 39
private function queryForShips()
{
$pdo = new PDO('mysql:host=localhost;dbname=oo_battle', 'root');
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$statement = $pdo->prepare('SELECT * FROM ship');
$statement->execute();
$shipsArray = $statement->fetchAll(PDO::FETCH_ASSOC);
return $shipsArray;
}
}

Head back up, call this method, then remove the original code:

50 lines | lib/ShipLoader.php
// ... lines 1 - 2
class ShipLoader
{
public function getShips()
{
$ships = array();
$shipsData = $this->queryForShips();
var_dump($shipsData);die;
// ... lines 11 - 37
}
// ... lines 39 - 49
}

Make sure things still work - cool! Now, why did we do this? Well, we had a chunk of code that did something - it made a query. Moving it into its own function has two advantages. First, we can re-use it later if we need to. But more importantly, it gives the code a name: queryForShips(). Now it's easy to see what it does - a lot easier than when this was stuck in the middle of other code.

So, creating private functions to help split code into small chunks is awesome.

Give me Objects!

Back to the ship factory to create ship objects from the array we have now.

In getShips(), I'll rename the variable to $shipsData - it sounds cool to me. Now, loop over $shipsData as $shipData. Each time we loop, we'll create a Ship object: $ship = new Ship() and pass $shipData['name'] as the only argument:

33 lines | lib/ShipLoader.php
// ... lines 1 - 4
public function getShips()
{
$ships = array();
$shipsData = $this->queryForShips();
foreach ($shipsData as $shipData) {
$ship = new Ship($shipData['name']);
// ... lines 13 - 17
}
// ... lines 19 - 20
}
// ... lines 22 - 33

Next, we can use the public functions to set the other data: $ship->setWeaponPower() and pass it $shipData['weapon_power']. Do the same for the jedi_factor and strength columns: $ship->setJediFactor() from the jedi_factor key and $ship->setStrength() from the strength key. The last column - is_under_repair we'll save that one for later. Can't have all the fun stuff at once! Finish the loop by putting $ship into the $ships array:

33 lines | lib/ShipLoader.php
// ... lines 1 - 4
public function getShips()
{
$ships = array();
$shipsData = $this->queryForShips();
foreach ($shipsData as $shipData) {
$ship = new Ship($shipData['name']);
$ship->setWeaponPower($shipData['weapon_power']);
$ship->setJediFactor($shipData['jedi_factor']);
$ship->setStrength($shipData['strength']);
$ships[] = $ship;
}
return $ships;
}
// ... lines 22 - 33

Wasn't that easy? Now get rid of all of the hardcoded Ship objects. We have less code than we started. That's always my preference.

We've only changed this one file, but we're ready! Refresh! Welcome to our dynamic application in under 10 minutes. Ship it!