1,106   Laravel MySQL

一,配置过程:

 

Laravel5读写分离配置比较简单,只需修改config/database.php,下面以MySQL数据库为例
内容如下

'mysql' => [
    'read' => [
        'host' => '192.168.1.1'
    ],
    'write' => [
        'host' => '196.168.1.2'
    ],
    'driver'    => 'mysql',
    'database'  => 'database',
    'username'  => 'root',
    'password'  => '',
    'charset'   => 'utf8',
    'collation' => 'utf8_unicode_ci',
    'prefix'    => '',
]

 

设置完毕之后,Laravel5默认将select的语句让read指定的数据库执行,insert/update/delete则交给write指定的数据库,达到读写分离的作用。
这些设置对原始查询raw queries,查询生成器query builder,以及对象映射 Eloquent 都生效。
官网解释如下

Sometimes you may wish to use one database connection for SELECT statements, and another for INSERT, UPDATE, and DELETE statements. Laravel makes this a breeze, and the proper connections will always be used whether you are using raw queries, the query builder, or the Eloquent ORM

 

二,实现原理

 

Laravel5读写分离主要有两个过程:
第一步,根据database.php配置,创建写库和读库的链接connection
第二步,调用select时先判断使用读库还是写库,而insert/update/delete统一使用写库

 

三,源码分析:根据database.php配置,创建写库和读库的链接connection

 

主要文件:Illuminate/Database/Connectors/ConnectionFactory.php
来看看几个重要的函数:

 

1,判断database.php是否配置了读写分离数据库

 

    /**
     * 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)
    {
        $config = $this->parseConfig($config, $name);
        // 如果配置了读写分离,则同时创建读库和写库的链接
        if (isset($config['read'])) {
            return $this->createReadWriteConnection($config);
        }
        // 如果没有配置,默认创建单个数据库链接
        return $this->createSingleConnection($config);
    }

 

 

2,看看如何创建读库和写库的链接

 

    /**
     * Create a single database connection instance.
     *
     * @param  array  $config
     * @return \Illuminate\Database\Connection
     */
    protected function createReadWriteConnection(array $config)
    {
        // 获取写库的配置信息,并创建链接
        $connection = $this->createSingleConnection($this->getWriteConfig($config));
        // 创建读库的链接
        return $connection->setReadPdo($this->createReadPdo($config));
    }

 

3,多个读库会选择哪个呢

 

    /**
     * Get the read configuration for a read / write connection.
     *
     * @param  array  $config
     * @return array
     */
    protected function getReadConfig(array $config)
    {
        $readConfig = $this->getReadWriteConfig($config, 'read');

        // 如果数组即多个读库,那么通过随机函数array_rand()挑一个,默认取第一个
        if (isset($readConfig['host']) && is_array($readConfig['host'])) {
            $readConfig['host'] = count($readConfig['host']) > 1
                ? $readConfig['host'][array_rand($readConfig['host'])]
                : $readConfig['host'][0];
        }
        return $this->mergeReadWriteConfig($config, $readConfig);
    }

 

4,写库也是随机选择的

 

    /**
     * Get a read / write level configuration.
     *
     * @param  array   $config
     * @param  string  $type
     * @return array
     */
    protected function getReadWriteConfig(array $config, $type)
    {

        // 如果多个,那么通过随机函数array_rand()挑一个
        if (isset($config[$type][0])) {
            return $config[$type][array_rand($config[$type])];
        }
        return $config[$type];
    }

 

总结:
1,可以设置多个读库和多个写库,或者不同组合,比如一个写库两个读库
2,每次只创建一个读库链接和一个写库链接,从多个库中随机选择一个;

 

四,源码分析:调用select时先判断使用读库还是写库,而insert/update/delete统一使用写库

 

主要文件:Illuminate/Database/Connection.php
看看几个重要的函数

 

1,select函数根据第三个输入参数判断使用读库还是写库

 

/**
     * Run a select statement against the database.
     *
     * @param  string  $query
     * @param  array  $bindings
     * @param  bool  $useReadPdo
     * @return array
     */
    public function select($query, $bindings = [], $useReadPdo = true)
    {
        return $this->run($query, $bindings, function ($me, $query, $bindings) use ($useReadPdo) {
            if ($me->pretending()) {
                return [];
            }

            // For select statements, we'll simply execute the query and return an array
            // of the database result set. Each element in the array will be a single
            // row from the database table, and will either be an array or objects.
            // 根据$useReadPdo参数,判断使用读库还是写库;
            // true使用读库,false使用写库;默认使用读库
            $statement = $this->getPdoForSelect($useReadPdo)->prepare($query);

            $statement->execute($me->prepareBindings($bindings));

            $fetchArgument = $me->getFetchArgument();

            return isset($fetchArgument) ?
                $statement->fetchAll($me->getFetchMode(), $fetchArgument, $me->getFetchConstructorArgument()) :
                $statement->fetchAll($me->getFetchMode());
        });
    }

    /**
     * Get the PDO connection to use for a select query.
     *
     * @param  bool  $useReadPdo
     * @return \PDO
     */
    protected function getPdoForSelect($useReadPdo = true)
    {
        // 根据$useReadPdo参数,选择PDO即判断使用读库还是写库;
        // true使用读库getReadPdo,false使用写库getPdo; 
       return $useReadPdo ? $this->getReadPdo() : $this->getPdo();
    }

 

2, insert/update/delete统一使用写库

 

 

    /**
     * Run an insert statement against the database.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return bool
     */
    public function insert($query, $bindings = [])
    {
        return $this->statement($query, $bindings);
    }

    /**
     * Run an update statement against the database.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return int
     */
    public function update($query, $bindings = [])
    {
        return $this->affectingStatement($query, $bindings);
    }

    /**
     * Run a delete statement against the database.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return int
     */
    public function delete($query, $bindings = [])
    {
        return $this->affectingStatement($query, $bindings);
    }

    /**
     * Execute an SQL statement and return the boolean result.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return bool
     */
    public function statement($query, $bindings = [])
    {
        return $this->run($query, $bindings, function ($me, $query, $bindings) {
            if ($me->pretending()) {
                return true;
            }

            $bindings = $me->prepareBindings($bindings);
            // 直接调用写库
            return $me->getPdo()->prepare($query)->execute($bindings);
        });
    }

    /**
     * Run an SQL statement and get the number of rows affected.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return int
     */
    public function affectingStatement($query, $bindings = [])
    {
        return $this->run($query, $bindings, function ($me, $query, $bindings) {
            if ($me->pretending()) {
                return 0;
            }

            // For update or delete statements, we want to get the number of rows affected
            // by the statement and return that back to the developer. We'll first need
            // to execute the statement and then we'll use PDO to fetch the affected.
            // 直接调用写库
            $statement = $me->getPdo()->prepare($query);

            $statement->execute($me->prepareBindings($bindings));

            return $statement->rowCount();
        });
    }




总结:
1,getReadPdo()获得读库链接,getPdo()获得写库链接;
2,select()函数根据第三个参数判断使用读库还是写库;

 

五,强制使用写库

 

有时候,我们需要读写实时一致,写完数据库后,想马上读出来,那么读写都指定一个数据库即可。
虽然Laravel5配置了读写分离,但也提供了另外的方法强制读写使用同一个数据库。

 

实现原理:上面$this->select()时指定使用写库的链接,即第三个参数useReadPdo设置为false即可

 

有几个方法可实现

1,调用方法

DB::table('posts')->selectFromWriteConnection('*')->where('id', $id);

 

源码解释:通过selectFromWriteConnection()函数

主要文件:Illuminate/Database/Connection.php

 

 

    /**
     * Run a select statement against the database.
     *
     * @param  string  $query
     * @param  array   $bindings
     * @return array
     */
    public function selectFromWriteConnection($query, $bindings = [])
    {
        ,
        // 上面有解释$this->select()函数的第三个参数useReadPdod的意义
        // 第三个参数是 false,所以 select 时会使用写库,而不是读库
        return $this->select($query, $bindings, false);
    }

 

 

 

2,调用方法

 

User::onWriteConnection()->find($id);

 

源码解释:通过onWriteConnection()函数

主要文件:Illuminate/Database/Eloquent/Model

 

    /**
     * Begin querying the model on the write connection.
     *
     * @return \Illuminate\Database\Query\Builder
     */
    public static function onWriteConnection()
    {
        $instance = new static;
        // query builder 指定使用写库
        return $instance->newQuery()->useWritePdo();
    }

 

看看query builder如何指定使用写库
主要文件:Illuminate/Database/Query/Builder

 

    /**
     * Use the write pdo for query.
     *
     * @return $this
     */
    public function useWritePdo()
    {
        // 指定使用写库,useWritePdo 为true
        $this->useWritePdo = true;

        return $this;
    }

    /**
     * Run the query as a "select" statement against the connection.
     *
     * @return array
     */
    protected function runSelect()
    {
        // 执行select时,useWritePdo原值为true,这里取反,被改成false;
        // 即$this->select()函数第三个参数为false,所以使用写库;
        return $this->connection->select($this->toSql(), $this->getBindings(), ! $this->useWritePdo);
    }


 

 




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