Illuminate\Database\DatabaseServiceProvider@registerConnectionServices

registerConnectionSerivces.php

<?php 
    /**
     * Register the primary database bindings.
     *
     * @return void
     */
    protected function registerConnectionServices()
    {
        // The connection factory is used to create the actual connection instances on
        // the database. We will inject the factory into the manager so that it may
        // make the connections while they are actually needed and not of before.
        $this->app->singleton('db.factory', function ($app) {
            return new ConnectionFactory($app);
        });
        // The database manager is used to resolve various connections, since multiple
        // connections might be managed. It also implements the connection resolver
        // interface which may be used by other components requiring connections.
        $this->app->singleton('db', function ($app) {
            return new DatabaseManager($app, $app['db.factory']);
        });
        $this->app->bind('db.connection', function ($app) {
            return $app['db']->connection();
        });
    }