Should all dependencies be loaded on every request? - php

Question

Hello I am making a PHP application using Silex and I want to use Dependency Injection. For Dependency Injection I need to load the dependencies into the container. I have one file that contains all definitions of what to load into the container called di.php it looks like this.
/**
* DI.php
*/
$app['db.connection'] = function() use($app) {
return new Connection([
'dbname' => $app['dbname'],
'dbuser' => $app['dbuser'],
'dbpass' => $app['dbpass'],
'dbhost' => $app['dbhost'],
]);
};
$app['user.repository'] = function() use($app) {
return new UserRepository($app['db.connection']);
};
$app['post.repository'] = function() use($app) {
return new PostRepository($app['db.connection']);
};
$app['index.controller'] = function() use($app) {
return new IndexController($app['user.repository']);
};
$app['post.controller'] = function() use($app) {
return new PostController($app['post.repository']);
};
But this file is requested on every request and all dependencies are loaded into the container, my question is how can I load the dependencies that I only need for one request and not all.

Answer 1

As #deceze says in their comment (shoulda made it an answer!), all you are "loading" on each request is a bunch of function expression statements. You can basically look at your providers as "classes" wherein the function declarations are done as function expressions rather than function statements. As per a normal class, the functions don't run simply cos you define them, right? No. You need to actually call them before they do anything.
The code within the function expression assigned to the $app['db.connection'] service is only executed if you use $app['db.connection']. Otherwise all you've done is defined a variable holding a function.
Obviously in the case of $app['db.connection'] you are more than likely gonna be using it every request one way or another. But for argument's sake $app['post.repository'] will only have its callback executed if you actively use $app['post.repository'] in that request.
Make sense? I can elaborate further if not.