我独自走进 Laravel5.5 的❤（九）

关于 laravel 的数据库驱动启动流程

1. 配置
   我们都知道，要配置 laravel 项目的数据库，要在 .env 中配置下面几个参数

   DB_CONNECTION
   DB_HOST
   DB_PORT
   DB_DATABASE
   DB_USERNAME
   DB_PASSWORD

   我们也知道这几个参数会在配置文件 config/database.php 中被引用

   'connections' => [
   
       'sqlite' => [
           'driver' => 'sqlite',
           'database' => env('DB_DATABASE', database_path('database.sqlite')),
           'prefix' => '',
       ],
   
       'mysql' => [
           'driver' => 'mysql',
           'host' => env('DB_HOST', '127.0.0.1'),
           'port' => env('DB_PORT', '3306'),
           'database' => env('DB_DATABASE', 'forge'),
           'username' => env('DB_USERNAME', 'forge'),
           'password' => env('DB_PASSWORD', ''),
           'unix_socket' => env('DB_SOCKET', ''),
           'charset' => 'utf8mb4',
           'collation' => 'utf8mb4_unicode_ci',
           'prefix' => '',
           'strict' => false,
           'engine' => null,
       ],
   
       'pgsql' => [
           'driver' => 'pgsql',
           'host' => env('DB_HOST', '127.0.0.1'),
           'port' => env('DB_PORT', '5432'),
           'database' => env('DB_DATABASE', 'forge'),
           'username' => env('DB_USERNAME', 'forge'),
           'password' => env('DB_PASSWORD', ''),
           'charset' => 'utf8',
           'prefix' => '',
           'schema' => 'public',
           'sslmode' => 'prefer',
       ],
   
       'sqlsrv' => [
           'driver' => 'sqlsrv',
           'host' => env('DB_HOST', 'localhost'),
           'port' => env('DB_PORT', '1433'),
           'database' => env('DB_DATABASE', 'forge'),
           'username' => env('DB_USERNAME', 'forge'),
           'password' => env('DB_PASSWORD', ''),
           'charset' => 'utf8',
           'prefix' => '',
       ],
   
   ],

   好的，眼前不止苟且，一起深入进去。
   2.数据库服务提供者
   在 config/app.php 中的 providers 中有注册
   Illuminate\Database\DatabaseServiceProvider::class,
   在Illuminate\Database\DatabaseServiceProvider::class,注册时会触发注册数据库连接服务

   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();
       });
   }

   3.连接工厂
   在连接工厂中，会根据配置的驱动不同生成不同的数据库连接器，真香

   public function createConnector(array $config)
   {
       if (! isset($config['driver'])) {
           throw new InvalidArgumentException('A driver must be specified.');
       }
   
       if ($this->container->bound($key = "db.connector.{$config['driver']}")) {
           return $this->container->make($key);
       }
   
      ** switch ($config['driver']) {
           case 'mysql':
               return new MySqlConnector;
           case 'pgsql':
               return new PostgresConnector;
           case 'sqlite':
               return new SQLiteConnector;
           case 'sqlsrv':
               return new SqlServerConnector;
       }**
   
       throw new InvalidArgumentException("Unsupported driver [{$config['driver']}]");
   }

   4.连接器
   在各个 Connector 中都会有一个连接方法 connect，
   在 connect() 中会生成一个 连接

   $connection = $this->createConnection(
           **$this->getDsn($config),** $config, $this->getOptions($config)
       );

   注意这里有一个 getDsn()，这个方法会返回一个特定的 PDO 驱动程序的名称，例如 mysql 会返回

   mysql:host=127.0.0.1;port=3306;dbname=homestead"

   4.1关于createConnection()

   public function createConnection($dsn, array $config, array $options)
   {
       list($username, $password) = [
           $config['username'] ?? null, $config['password'] ?? null,
       ];
   
       try {
           return $this->createPdoConnection(
               $dsn, $username, $password, $options
           );
       } catch (Exception $e) {
           return $this->tryAgainIfCausedByLostConnection(
               $e, $dsn, $username, $password, $options
           );
       }
   }

   这里可以看到获取数据库用户名和密码，然后创建一个 pdo 连接
   4.2关于createPdoConnection()

   protected function createPdoConnection($dsn, $username, $password, $options)
   {
       if (class_exists(PDOConnection::class) && ! $this->isPersistentConnection($options)) {
           return new **PDOConnection($dsn, $username, $password, $options)**;
       }
   
       return new PDO($dsn, $username, $password, $options);
   }

   4.3关于 PDOConnection
   Doctrine/DBAL/Driver/PDOConnection::class 其实是一个继承了 PDO 的类，重新封装了 exec()、query()等一些方法
   具体可以 github 上观摩。
   https://github.com/doctrine/dbal/blob/mast...

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至此，
致敬知识。

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