Doctrine MasterSlaveConnection connect sets $this->_conn to the master one

MasterSlaveConnection.php

<?php

class MasterSlaveConnection
{
    public function connect($connectionName = 'slave')
    {
        if ( $connectionName !== 'slave' && $connectionName !== 'master' ) {
            throw new \InvalidArgumentException("Invalid option to connect(), only master or slave allowed.");
        }

        $forceMasterAsSlave = false;

        if ($this->getTransactionNestingLevel() > 0) {
            $connectionName = 'master';
            $forceMasterAsSlave = true;
        }

        if ($this->connections[$connectionName]) {
            if ($forceMasterAsSlave) {
                $this->connections['slave'] = $this->_conn = $this->connections['master'];
            } else {
                // **** this is the connection that is set up ***
                $this->_conn = $this->connections[$connectionName];
            }
            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;
    }
}