public function getStructureNodes(Criteria $criteria = null, ConnectionInterface $con = null)
    {
        $partial = $this->collStructureNodesPartial && !$this->isNew();
        if (null === $this->collStructureNodes || null !== $criteria  || $partial) {
            if ($this->isNew() && null === $this->collStructureNodes) {
                // return empty collection
                $this->initStructureNodes();
            } else {
                $collStructureNodes = ChildStructureNodeQuery::create(null, $criteria)
                    ->filterBySkill($this)
                    ->find($con);

                if (null !== $criteria) {
                    if (false !== $this->collStructureNodesPartial && count($collStructureNodes)) {
                        $this->initStructureNodes(false);

                        foreach ($collStructureNodes as $obj) {
                            if (false == $this->collStructureNodes->contains($obj)) {
                                $this->collStructureNodes->append($obj);
                            }
                        }

                        $this->collStructureNodesPartial = true;
                    }

                    return $collStructureNodes;
                }

                if ($partial && $this->collStructureNodes) {
                    foreach ($this->collStructureNodes as $obj) {
                        if ($obj->isNew()) {
                            $collStructureNodes[] = $obj;
                        }
                    }
                }

                $this->collStructureNodes = $collStructureNodes;
                $this->collStructureNodesPartial = false;
            }
        }

        return $this->collStructureNodes;
    }