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~