Doctrine\DBAL\Connections\MasterSlaveConnection::connect PHP Метод

    public function connect($connectionName = null)
    {
        $requestedConnectionChange = $connectionName !== null;
        $connectionName = $connectionName ?: 'slave';
        if ($connectionName !== 'slave' && $connectionName !== 'master') {
            throw new \InvalidArgumentException("Invalid option to connect(), only master or slave allowed.");
        }
        // If we have a connection open, and this is not an explicit connection
        // change request, then abort right here, because we are already done.
        // This prevents writes to the slave in case of "keepSlave" option enabled.
        if (isset($this->_conn) && $this->_conn && !$requestedConnectionChange) {
            return false;
        }
        $forceMasterAsSlave = false;
        if ($this->getTransactionNestingLevel() > 0) {
            $connectionName = 'master';
            $forceMasterAsSlave = true;
        }
        if (isset($this->connections[$connectionName]) && $this->connections[$connectionName]) {
            $this->_conn = $this->connections[$connectionName];
            if ($forceMasterAsSlave && !$this->keepSlave) {
                $this->connections['slave'] = $this->_conn;
            }
            return false;
        }
        if ($connectionName === 'master') {
            // Set slave connection to master to avoid invalid reads
            if ($this->connections['slave'] && !$this->keepSlave) {
                unset($this->connections['slave']);
            }
            $this->connections['master'] = $this->_conn = $this->connectTo($connectionName);
            if (!$this->keepSlave) {
                $this->connections['slave'] = $this->connections['master'];
            }
        } else {
            $this->connections['slave'] = $this->_conn = $this->connectTo($connectionName);
        }
        if ($this->_eventManager->hasListeners(Events::postConnect)) {
            $eventArgs = new ConnectionEventArgs($this);
            $this->_eventManager->dispatchEvent(Events::postConnect, $eventArgs);
        }
        return true;
    }

 /**
  * @param MasterSlaveConnection $connection
  * @return Success|Failure
  */
 private function checkMasterSlaveConnection(MasterSlaveConnection $connection)
 {
     // TODO Check all slaves, instead of random one if possible.
     $connection->connect('slave');
     $isSlaveConnected = $connection->ping();
     $connection->connect('master');
     $isMasterConnected = $connection->ping();
     $data = ['slave' => $isSlaveConnected ? 'connected' : 'not connected', 'master' => $isMasterConnected ? 'connected' : 'not connected'];
     if ($isMasterConnected && $isSlaveConnected) {
         return new Success(get_class($connection), $data);
     }
     return new Failure(get_class($connection), $data);
 }