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07.

Centralized Configuration

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Centralized Configuration

The homepage is loading pet data from the database, but our contact page isn’t:

It lists a different number of pets than we know we have in the database. Silly contact page. the problem is that get_pets() is still reading from the pets.json file, instead of using the database.

So instead of putting our query logic right inside of index.php, why not just update get_pets() to pull from the database?

Copy all of the database-code and paste it into get_pets(), which lives in the lib/functions.php file. Make sure to return the queried data:

// lib/functions.php
function get_pets()
{
    $pdo = new PDO('mysql:dbname=air_pup;host=localhost', 'root', null);
    $result = $pdo->query('SELECT * FROM pet');
    $pets = $result->fetchAll();

    return $pets;
}

Try out the contact page! Now that get_pets() queries the database, this shows that we have 2 slobbery pets.

Back in index.php, remove the database stuff and uncomment out the line that calls get_pets():

// index.php
require 'lib/functions.php';

$pets = get_pets();
// ...

This works and now all our heavy-lifting lives inside functions. It’s not perfect, but our code is getting better!

Creating a Configuration File

To make it easier to control your app, configuration - like your database username and password - is usually isolated into its own file. Let’s create a new file called config.php. Open up PHP and create a new associative array with the databse connection string, the username and the password:

// lib/config.php

$config = array(
    'database_dsn'  => 'mysql:dbname=air_pup;host=localhost',
    'database_user' => 'root',
    'database_pass' => null,
);

Tip

DSN stands for “data source name” - the fancy name for the connection string.

If we open this file in the browser, nothing happens:

But we expected that: the config file doesn’t echo anything, it just sets a PHP variable. This file isn’t meant to be a page. Instead, we’re going to require it from other files and use this $config variable.

Let’s do this in get_pets(). Replace each argument to PDO with a key from the $config variable:

// lib/functions.php

function get_pets()
{
    require 'config.php';

    $pdo = new PDO(
        $config['database_dsn'],
        $config['database_user'],
        $config['database_pass']
    );

    // ...
}

We we refresh, it still works! Remember that require is a function that basically copies and pastes the contents of another file into this one. My editor thinks $config is undefined, but we know better than that!

Returning from an Included File

I don’t love this. Rename $config to $configVars in config.php:

// lib/config.php
$configVars = array(
    'database_dsn'  => 'mysql:dbname=air_pup;host=localhost',
    'database_user' => 'root',
    'database_pass' => null,
);

This change looks safe. I mean, it’s not like we’re using this variable anywhere inside this file. But when we refresh, things explode! We are referencing the old $config variable inside get_pets, but that wasn’t very obvious.

Remember how we can return values from a function? We can do the same from included files:

// lib/config.php
$configVars = array(
    'database_dsn'  => 'mysql:dbname=air_pup;host=localhost',
    'database_user' => 'root',
    'database_pass' => null,
);

return $configVars;

Now, instead of relying on whatever we called that variable in config.php, create a new variable when you require it:

// lib/functions.php
function get_pets()
{
    $config = require 'config.php';

    $pdo = new PDO(
        $config['database_dsn'],
        $config['database_user'],
        $config['database_pass']
    );

    // ...
}
// ...

Try it! It works again. We’re using this file almost like a function: require it and set its return value to a variable. Most included files won’t have a return line, but it’s really common for configuration.

So hey, we have a configuration file! The advantage of putting all this stuff into one spot is that you can quickly find and control all the little values that make your app tick. This also makes our app easier to share with another developer. If the database password on their computer is different, they don’t need to dig deep around in your code to find where you hid that. We’re starting to get organized!