laravel5.5源碼筆記（七、數據庫初始化）

laravel中的數據庫也是以服務提供者進行初始化的名為DatabaseServiceProvider，在config文件的providers數組中有寫。路徑為vendor\laravel\framework\src\Illuminate\Database\DatabaseServiceProvider.php

跟以往的serviceProvider一樣在register方法中注冊，在boot方法中引導加載。

來看一下register方法。為了保險起見它先通過Model將之前的加載數據給清除掉了。隨后開始注冊各種數據庫連接所用到的對象，通過singleton方法注冊一個單例的延遲加載對象到容器中。將DB門面類綁定到了DatabaseManager類中。

 

    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;
        });
    }

 

數據庫連接對象ConnectionFactory。這個連接工廠類之中的各種方法都是在創建配置，以及通過配置數組，返回對應的數據庫連接實例。這個類中的方法大多是對數據庫的連接做一些配置，然后根據這些配置來返回相應的數據庫連接實例。

    /**
     * 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]");
    }

 

數據庫管理對象DatabaseManager。這個數據庫管理類之中的各種方法也是通過各種數據庫配置來調用ConnectionFactory工廠來返回數據庫連接實例，它會通過配置read,write來返回相應的讀寫pdo實例。以及包含了數據庫實例的創建與斷開銷毀等。set、get各種配置。如setPdoForType方法來設置數據庫連接的讀寫分離（設置只讀、只寫）。那么這個類的上游方法在哪里呢。它是從哪里被調用的呢？我們開頭提了一句，DB門面類所綁定的類，就是這個類，但是如果我們去這個類中尋找常用的talbe()、query()等方法，肯定是一無所獲的，不過我們會發現__call()方法，這個魔術方法會在調用不存在的方法時執行，看一下它的內容。它只有一句代碼，從$this->connection()這個對象中，執行相應的方法並返回結果。是的，laravel的源碼封裝度太高了，這里我們暫時只需要知道$this->connection()代表了數據庫連接實例就好。

public function __call($method, $parameters)
    {
        return $this->connection()->$method(...$parameters);
    }

 

 

剛剛說到數據庫連接實例，現在我們就來探尋這個實例是如何被創建出來的。如下makeConnection方法所示，通過剛剛說到的ConnectionFactory來返回數據庫連接實例。

    /**
     * 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如何創建出數據庫連接實例，又要把視線跳到之前說的ConnectionFactory類中了。$this->factory->make($config, $name);最后返回了make方法，我們就從這個方法入手，請看下列代碼。

    /**
     * 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)
    {
        //合並配置數組
        $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，經過一系列的方法跳轉，我們終於通過數據庫配置，得到了mysql等數據庫的連接對象。

 

數據庫工廠類ConnectionFactory返回的實例連接，我們拿mysql舉例。返回的便是MySqlConnection這個類\vendor\laravel\framework\src\Illuminate\Database\MySqlConnection.php

進入這個類文件，可以看見都是獲取grammar相關的方法，這些方法暫時先不去看它。秘密在於它的父類Connection類。（\vendor\laravel\framework\src\Illuminate\Database\Connection.php）先看它的構造方法，從這個方法我們可以知道，所有模型對象也好，DB對象也好，底層都是通過pdo去連接執行的，另外呢，tablePrefix數據表前綴，以及數據庫連接配置也是在這里進行加載的。useDefaultQueryGrammar這倆個方法就不去深究了。我們來看點有趣的。

    /**
     * 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？就是這個table()方法了。我們都知道，在laravel中既可以使用模型的方式去進行數據庫操作，也可以使用DB::table()的方式，而我們平時使用較多的table()方法的真身，就在這個類里了。這個table方法只做了一件事，就是從$this->query()這個對象中from一個表，然后返回的對象就可以通過鏈式調用的方式去做其他操作了。接下來看這個$this->query()，這個方法也只做了一件事，new一個QueryBuilder對象。

    /**
     * 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這個對象就是我們平時使用的eloquent orm 的入口，我們平時使用的那些方便的數據庫操作方法都是從這里進入。

 通過一系列跳轉，我們會發現，這個QueryBuilder的真身在

\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php這個類中，名為Builder類。

來到這個類文件中，稍微瀏覽一下，感覺發現了寶藏，里面那些where()、join()、get()、find()方法，不正是我們常用的各種方便的orm方法么？

來來回回繞了這么大一個圈終於找到，我們常用的函數是從何而來，但是現在還有一個疑問了。現在我們一路跟蹤到的線索，都是從DB::table()這種方式跟蹤而來，那么model的方式是怎么調用的呢？

讓我們隨便新建一個模型類，然后找到它的父類Model

vendor\laravel\framework\src\Illuminate\Database\Eloquent\Model.php

瀏覽一番過后，我們發現了比較眼熟的fill()、all()、save()等方法，然后我們會發現這些方法中，大部分都有$this->newModelQuery();這么一句，我們根據這一線索一路跟蹤，一路尾行，最終我們會發現new QueryBuilder這句代碼又出現了。

    /**
     * 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，再次跳轉后，我們便又回到了\vendor\laravel\framework\src\Illuminate\Database\Query\Builder.php這個類中。

至於那些model里沒寫的方法為什么可以直接調用？你去model類里找一找看有沒有__call這個魔術方法，看它里面寫了些什么

    /**
     * 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);
    }

 

 

到這里，數據庫服務是怎么啟動的，DB門面、model類為什么能直接執行orm方法，相信我們已經有清晰的認識了。至於orm是怎么轉化成sql語句執行的，且聽下回分解~