Phactory\Sql\Association\ManyToMany::_guessToJoinColumn PHP Method

    protected function _guessToJoinColumn()
    {
        if (null === $this->_to_join_column) {
            $guess = $this->_to_table->getSingularName() . '_id';
            if ($this->_join_table->hasColumn($guess)) {
                $this->setToJoinColumn($guess);
            } else {
                throw new \Exception("Unable to guess from_join_column and none specified");
            }
        }
    }