laravel5.5源码笔记（七、数据库初始化）
laravel中的数据库也是以服务提供者进行初始化的名为DatabaseServiceProvider，在config文件的providers数组中有写。路径为vendor\laravel\framework\src\Illuminate\Database\DatabaseServiceProvider.php
跟以往的serviceProvider一样在register方法中注册，在boot方法中引导加载。
来看一下register方法。为了保险起见它先通过Model将之前的加载数据给清除掉了。随后开始注册各种数据库连接所用到的对象，通过singleton方法注册一个单例的延迟加载对象到容器中。将DB门面类绑定到了DatabaseManager类中。
public function register() { Model::clearBootedModels(); $this->registerConnectionServices(); $this->registerEloquentFactory(); $this->registerQueueableEntityResolver(); } 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(); }); } /** * Register the Eloquent factory instance in the container. * * @return void */ protected function registerEloquentFactory() { $this->app->singleton(FakerGenerator::class, function ($app) { return FakerFactory::create($app['config']->get('app.faker_locale', 'en_US')); }); $this->app->singleton(EloquentFactory::class, function ($app) { return EloquentFactory::construct( $app->make(FakerGenerator::class), $this->app->databasePath('factories') ); }); } /** * Register the queueable entity resolver implementation. * * @return void */ protected function registerQueueableEntityResolver() { $this->app->singleton(EntityResolver::class, function () { return new QueueEntityResolver; }); }
数据库连接对象ConnectionFactory。这个连接工厂类之中的各种方法都是在创建配置，以及通过配置数组，返回对应的数据库连接实例。这个类中的方法大多是对数据库的连接做一些配置，然后根据这些配置来返回相应的数据库连接实例。
/** * Create a new connection instance. * * @param string $driver * @param \PDO|\Closure $connection * @param string $database * @param string $prefix * @param array $config * @return \Illuminate\Database\Connection * * @throws \InvalidArgumentException */ protected function createConnection($driver, $connection, $database, $prefix = '', array $config = []) { if ($resolver = Connection::getResolver($driver)) { return $resolver($connection, $database, $prefix, $config); } switch ($driver) { case 'mysql': return new MySqlConnection($connection, $database, $prefix, $config); case 'pgsql': return new PostgresConnection($connection, $database, $prefix, $config); case 'sqlite': return new SQLiteConnection($connection, $database, $prefix, $config); case 'sqlsrv': return new SqlServerConnection($connection, $database, $prefix, $config); } throw new InvalidArgumentException("Unsupported driver [$driver]"); }
数据库管理对象DatabaseManager。这个数据库管理类之中的各种方法也是通过各种数据库配置来调用ConnectionFactory工厂来返回数据库连接实例，它会通过配置read,write来返回相应的读写pdo实例。以及包含了数据库实例的创建与断开销毁等。set、get各种配置。如setPdoForType方法来设置数据库连接的读写分离（设置只读、只写）。那么这个类的上游方法在哪里呢。它是从哪里被调用的呢？我们开头提了一句，DB门面类所绑定的类，就是这个类，但是如果我们去这个类中寻找常用的talbe()、query()等方法，肯定是一无所获的，不过我们会发现__call()方法，这个魔术方法会在调用不存在的方法时执行，看一下它的内容。它只有一句代码，从$this->connection()这个对象中，执行相应的方法并返回结果。是的，laravel的源码封装度太高了，这里我们暂时只需要知道$this->connection()代表了数据库连接实例就好。
public function __call($method, $parameters) { return $this->connection()->$method(...$parameters); }
刚刚说到数据库连接实例，现在我们就来探寻这个实例是如何被创建出来的。如下makeConnection方法所示，通过刚刚说到的ConnectionFactory来返回数据库连接实例。
/** * Prepare the read / write mode for database connection instance. * * @param \Illuminate\Database\Connection $connection * @param string $type * @return \Illuminate\Database\Connection */ protected function setPdoForType(Connection $connection, $type = null) { if ($type == 'read') { $connection->setPdo($connection->getReadPdo()); } elseif ($type == 'write') { $connection->setReadPdo($connection->getPdo()); } return $connection; } /** * Make the database connection instance. * * @param string $name * @return \Illuminate\Database\Connection */ protected function makeConnection($name) { $config = $this->configuration($name); // First we will check by the connection name to see if an extension has been // registered specifically for that connection. If it has we will call the // Closure and pass it the config allowing it to resolve the connection. if (isset($this->extensions[$name])) { return call_user_func($this->extensions[$name], $config, $name); } // Next we will check to see if an extension has been registered for a driver // and will call the Closure if so, which allows us to have a more generic // resolver for the drivers themselves which applies to all connections. if (isset($this->extensions[$driver = $config['driver']])) { return call_user_func($this->extensions[$driver], $config, $name); } return $this->factory->make($config, $name); }
好的，看到DatabaseManager如何创建出数据库连接实例，又要把视线跳到之前说的ConnectionFactory类中了。$this->factory->make($config, $name);最后返回了make方法，我们就从这个方法入手，请看下列代码。
/** * Establish a PDO connection based on the configuration. * * @param array $config * @param string $name * @return \Illuminate\Database\Connection */ public function make(array $config, $name = null) { //合并配置数组 $config = $this->parseConfig($config, $name); if (isset($config['read'])) { return $this->createReadWriteConnection($config); } return $this->createSingleConnection($config); } /** * Create a single database connection instance. * * @param array $config * @return \Illuminate\Database\Connection */ protected function createSingleConnection(array $config) { $pdo = $this->createPdoResolver($config); return $this->createConnection( $config['driver'], $pdo, $config['database'], $config['prefix'], $config ); } /** * Create a new connection instance. * * @param string $driver * @param \PDO|\Closure $connection * @param string $database * @param string $prefix * @param array $config * @return \Illuminate\Database\Connection * * @throws \InvalidArgumentException */ protected function createConnection($driver, $connection, $database, $prefix = '', array $config = []) { if ($resolver = Connection::getResolver($driver)) { return $resolver($connection, $database, $prefix, $config); } switch ($driver) { case 'mysql': return new MySqlConnection($connection, $database, $prefix, $config); case 'pgsql': return new PostgresConnection($connection, $database, $prefix, $config); case 'sqlite': return new SQLiteConnection($connection, $database, $prefix, $config); case 'sqlsrv': return new SqlServerConnection($connection, $database, $prefix, $config); } throw new InvalidArgumentException("Unsupported driver [$driver]"); }
可以看到，经过一系列的方法跳转，我们终于通过数据库配置，得到了mysql等数据库的连接对象。
数据库工厂类ConnectionFactory返回的实例连接，我们拿mysql举例。返回的便是MySqlConnection这个类\vendor\laravel\framework\src\Illuminate\Database\MySqlConnection.php
进入这个类文件，可以看见都是获取grammar相关的方法，这些方法暂时先不去看它。秘密在于它的父类Connection类。（\vendor\laravel\framework\src\Illuminate\Database\Connection.php）先看它的构造方法，从这个方法我们可以知道，所有模型对象也好，DB对象也好，底层都是通过pdo去连接执行的，另外呢，tablePrefix数据表前缀，以及数据库连接配置也是在这里进行加载的。useDefaultQueryGrammar这俩个方法就不去深究了。我们来看点有趣的。
/** * Create a new database connection instance. * * @param \PDO|\Closure $pdo * @param string $database * @param string $tablePrefix * @param array $config * @return void */ public function __construct($pdo, $database = '', $tablePrefix = '', array $config = []) { $this->pdo = $pdo; // First we will setup the default properties. We keep track of the DB // name we are connected to since it is needed when some reflective // type commands are run such as checking whether a table exists. $this->database = $database; $this->tablePrefix = $tablePrefix; $this->config = $config; // We need to initialize a query grammar and the query post processors // which are both very important parts of the database abstractions // so we initialize these to their default values while starting. $this->useDefaultQueryGrammar(); $this->useDefaultPostProcessor(); }
有趣的是什么呢？就是这个table()方法了。我们都知道，在laravel中既可以使用模型的方式去进行数据库操作，也可以使用DB::table()的方式，而我们平时使用较多的table()方法的真身，就在这个类里了。这个table方法只做了一件事，就是从$this->query()这个对象中from一个表，然后返回的对象就可以通过链式调用的方式去做其他操作了。接下来看这个$this->query()，这个方法也只做了一件事，new一个QueryBuilder对象。
/** * Begin a fluent query against a database table. * * @param string $table * @return \Illuminate\Database\Query\Builder */ public function table($table) { return $this->query()->from($table); } /** * Get a new query builder instance. * * @return \Illuminate\Database\Query\Builder */ public function query() { return new QueryBuilder( $this, $this->getQueryGrammar(), $this->getPostProcessor() ); }
而QueryBuilder这个对象就是我们平时使用的eloquent orm 的入口，我们平时使用的那些方便的数据库操作方法都是从这里进入。
通过一系列跳转，我们会发现，这个QueryBuilder的真身在
\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php这个类中，名为Builder类。
来到这个类文件中，稍微浏览一下，感觉发现了宝藏，里面那些where()、join()、get()、find()方法，不正是我们常用的各种方便的orm方法么？
来来回回绕了这么大一个圈终于找到，我们常用的函数是从何而来，但是现在还有一个疑问了。现在我们一路跟踪到的线索，都是从DB::table()这种方式跟踪而来，那么model的方式是怎么调用的呢？
让我们随便新建一个模型类，然后找到它的父类Model
vendor\laravel\framework\src\Illuminate\Database\Eloquent\Model.php
浏览一番过后，我们发现了比较眼熟的fill()、all()、save()等方法，然后我们会发现这些方法中，大部分都有$this->newModelQuery();这么一句，我们根据这一线索一路跟踪，一路尾行，最终我们会发现new QueryBuilder这句代码又出现了。
/** * Get a new query builder for the model's table. * * @return \Illuminate\Database\Eloquent\Builder */ public function newQuery() { return $this->registerGlobalScopes($this->newQueryWithoutScopes()); } /** * Register the global scopes for this builder instance. * * @param \Illuminate\Database\Eloquent\Builder $builder * @return \Illuminate\Database\Eloquent\Builder */ public function registerGlobalScopes($builder) { foreach ($this->getGlobalScopes() as $identifier => $scope) { $builder->withGlobalScope($identifier, $scope); } return $builder; } /** * Get a new query builder instance for the connection. * * @return \Illuminate\Database\Query\Builder */ protected function newBaseQueryBuilder() { $connection = $this->getConnection(); return new QueryBuilder( $connection, $connection->getQueryGrammar(), $connection->getPostProcessor() ); }
是的，再次跳转后，我们便又回到了\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php这个类中。
至于那些model里没写的方法为什么可以直接调用？你去model类里找一找看有没有__call这个魔术方法，看它里面写了些什么
/** * Handle dynamic method calls into the model. * * @param string $method * @param array $parameters * @return mixed */ public function __call($method, $parameters) { if (in_array($method, ['increment', 'decrement'])) { return $this->$method(...$parameters); } return $this->newQuery()->$method(...$parameters); }
到这里，数据库服务是怎么启动的，DB门面、model类为什么能直接执行orm方法，相信我们已经有清晰的认识了。至于orm是怎么转化成sql语句执行的，且听下回分解~
