UnreachableParent: Eliminate duplicate nodes

Nodes might be referenced by multiple independent paths, which
might lead to the same root problem multiple times.

library/Icingadb/Model/UnreachableParent.php

@@ -5,6 +5,7 @@
 namespace Icinga\Module\Icingadb\Model;
 
 use Icinga\Module\Icingadb\Model\Behavior\ReRoute;
+use Icinga\Module\Icingadb\Model\UnreachableParent\ResultSet;
 use InvalidArgumentException;
 use ipl\Orm\Behavior\Binary;
 use ipl\Orm\Behaviors;
@@ -112,6 +113,8 @@ class UnreachableParent extends DependencyNode
             )
         ));
 
+        $query->setResultSetClass(ResultSet::class);
+
         return $query;
     }
 

library/Icingadb/Model/UnreachableParent/ResultSet.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Icinga\Module\Icingadb\Model\UnreachableParent;
+
+use Icinga\Module\Icingadb\Redis\VolatileStateResults;
+use Traversable;
+
+class ResultSet extends VolatileStateResults
+{
+    protected function yieldTraversable(Traversable $traversable)
+    {
+        $knownIds = [];
+        foreach ($traversable as $value) {
+            if (isset($knownIds[$value->id])) {
+                continue;
+            }
+
+            $knownIds[$value->id] = true;
+
+            yield $value;
+        }
+    }
+}

library/Icingadb/Widget/Detail/ObjectDetail.php

@@ -655,7 +655,6 @@ class ObjectDetail extends BaseHtmlElement
                 'service.host',
                 'service.host.state'
             ])
-            ->setResultSetClass(VolatileStateResults::class)
             ->orderBy([
                 'host.state.severity',
                 'host.state.last_state_change',