public function setGroup(ChildGroup $v = null)
    {
        // aggregate_column_relation behavior
        if (null !== $this->aGroup && $v !== $this->aGroup) {
            $this->oldGroupSkillCount = $this->aGroup;
        }
        if ($v === null) {
            $this->setGroupId(NULL);
        } else {
            $this->setGroupId($v->getId());
        }

        $this->aGroup = $v;

        // Add binding for other direction of this n:n relationship.
        // If this object has already been added to the ChildGroup object, it will not be re-added.
        if ($v !== null) {
            $v->addSkillGroup($this);
        }


        return $this;
    }