public function registerJoinTable($joinTable)
    {
        if (! $joinTable instanceof JoinTable) {
            throw new RelationException("Join Table register failure!"); // @codeCoverageIgnore
        }

        // Check for existing
        if (isset($this->joinTables[$joinTable->name])) {
            // Ignore. We already have it, lets hope the user knows what he is doing!
            return; // @codeCoverageIgnore
        }

        // Add and make sure we don't have duplicates
        $this->joinTables[$joinTable->name] = $joinTable;
    }