diff --git a/.github/workflows/diagnostics.yml b/.github/workflows/diagnostics.yml
new file mode 100644
index 000000000..5a6384fe4
--- /dev/null
+++ b/.github/workflows/diagnostics.yml
@@ -0,0 +1,49 @@
+name: DC General
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        php: [7.3, 7.4]
+        contao: [~4.4.0, ~4.9.0]
+
+    steps:
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Pull source
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      # see https://github.com/shivammathur/setup-php
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Setup PHP.
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: ${{ matrix.php }}
+          coverage: none
+
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Cache composer cache directory
+        uses: actions/cache@v1
+        env:
+          cache-name: composer-cache-dir
+        with:
+          path: ~/.cache/composer
+          key: ${{ runner.os }}-build-${{ env.cache-name }}
+
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Cache vendor directory
+        uses: actions/cache@v1
+        env:
+          cache-name: composer-vendor
+        with:
+          path: vendor
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/composer.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Install composer dependencies
+        run: composer update --prefer-dist --no-interaction --no-suggest
+
+      - name: PHP ${{ matrix.php }} ${{ matrix.contao }} Run tests
+        run: ant -keep-going
diff --git a/.gitignore b/.gitignore
index d20d8c2c5..bb4ec17e4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,3 +19,7 @@ composer.lock
 .sass-cache
 build/
 .phpunit.result.cache
+
+# PHPCQ and related tools
+.php_cs.cache
+build.properties
diff --git a/.travis.yml b/.travis.yml
deleted file mode 100644
index e6017b991..000000000
--- a/.travis.yml
+++ /dev/null
@@ -1,43 +0,0 @@
-dist: xenial
-
-addons:
-    apt:
-        packages:
-            - ant-optional
-
-language: php
-
-php:
-    - "7.4"
-    - "7.3"
-    - "7.2"
-
-env:
-    - CONTAO_VERSION='contao/core-bundle ~4.10.0'
-    - CONTAO_VERSION='contao/core-bundle ~4.9.0'
-
-matrix:
-    fast_finish: true
-    exclude:
-        -   php: "7.1"
-            env: CONTAO_VERSION='contao/core-bundle ~4.9.0'
-        -   php: "7.1"
-            env: CONTAO_VERSION='contao/core-bundle ~4.10.0'
-
-before_install:
-    - echo "memory_limit = -1" > travis.php.ini && phpenv config-add travis.php.ini
-
-install:
-    - travis_retry composer self-update && composer --version
-    - travis_retry composer require $CONTAO_VERSION --no-update
-    - travis_retry composer update --prefer-dist --no-interaction
-
-script: ant -keep-going
-
-# Hack to make things work again - we can not use a shallow repository.
-git:
-    depth: 2147483647
-
-cache:
-    directories:
-        - vendor
diff --git a/README.md b/README.md
index 1f60fc716..ec6fbac14 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-[![Build Status](https://travis-ci.org/contao-community-alliance/dc-general.png)](https://travis-ci.org/contao-community-alliance/dc-general)
+[![Build Status](https://github.com/contao-community-alliance/dc-general/actions/workflows/diagnostics.yml/badge.svg)](https://github.com/contao-community-alliance/dc-general/actions)
 [![Latest Version tagged](http://img.shields.io/github/tag/contao-community-alliance/dc-general.svg)](https://github.com/contao-community-alliance/dc-general/tags)
 [![Latest Version on Packagist](http://img.shields.io/packagist/v/contao-community-alliance/dc-general.svg)](https://packagist.org/packages/contao-community-alliance/dc-general)
 [![Installations via composer per month](http://img.shields.io/packagist/dm/contao-community-alliance/dc-general.svg)](https://packagist.org/packages/contao-community-alliance/dc-general)
diff --git a/composer.json b/composer.json
index e31335d99..26bb50f52 100644
--- a/composer.json
+++ b/composer.json
@@ -81,5 +81,11 @@
     },
     "scripts": {
         "php-cs-fixer": "php-cs-fixer fix --rules=@PSR2"
+    },
+    "config": {
+        "allow-plugins": {
+            "contao-components/installer": false,
+            "contao/manager-plugin": true
+        }
     }
 }
diff --git a/src/Cache/Http/InvalidCacheTags.php b/src/Cache/Http/InvalidCacheTags.php
index 8b817460b..501117df1 100644
--- a/src/Cache/Http/InvalidCacheTags.php
+++ b/src/Cache/Http/InvalidCacheTags.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2020 Contao Community Alliance.
+ * (c) 2013-2021 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -12,7 +12,8 @@
  *
  * @package    contao-community-alliance/dc-general
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2020 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2021 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -146,7 +147,9 @@ private function addRelatedModelsTag(ModelInterface $model): void
 
         /** @var DefaultCollection $parentModels */
         $parentModels = $dataProvider
-            ->fetchAll($dataProvider->getEmptyConfig()->setFilter($parentCondition->getInverseFilterFor($model)));
+            ->fetchAll(
+                $dataProvider->getEmptyConfig()->setFilter((array) $parentCondition->getInverseFilterFor($model))
+            );
         foreach ($parentModels as $parentModel) {
             $this->addModelTag($parentModel);
         }
diff --git a/src/Contao/Subscriber/FallbackResetSubscriber.php b/src/Contao/Subscriber/FallbackResetSubscriber.php
index b4fa5fda3..2fef1feb2 100644
--- a/src/Contao/Subscriber/FallbackResetSubscriber.php
+++ b/src/Contao/Subscriber/FallbackResetSubscriber.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2021 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -14,13 +14,15 @@
  * @author     Christian Schiffler <c.schiffler@cyberspectrum.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2021 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
 
 namespace ContaoCommunityAlliance\DcGeneral\Contao\Subscriber;
 
+use ContaoCommunityAlliance\DcGeneral\Controller\ModelCollector;
 use ContaoCommunityAlliance\DcGeneral\Data\ConfigInterface;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelManipulator;
 use ContaoCommunityAlliance\DcGeneral\Event\AbstractModelAwareEvent;
@@ -160,9 +162,11 @@ private function determineFilterConfig(AbstractModelAwareEvent $event)
         );
 
         if (null !== $parentFilter) {
-            $parentConfig   = $dataProvider->getEmptyConfig()->setFilter($parentFilter->getInverseFilterFor($model));
-            $parentProvider = $environment->getDataProvider($parentFilter->getSourceName());
-            $parent         = $parentProvider->fetchAll($parentConfig)->get(0);
+            $parent = (new ModelCollector($environment))->searchParentOf($model);
+            if ($parent === null) {
+                return null;
+            }
+
             return $dataProvider->getEmptyConfig()->setFilter($parentFilter->getFilter($parent));
         }
 
diff --git a/src/Contao/View/Contao2BackendView/ActionHandler/ParentedListViewShowAllHandler.php b/src/Contao/View/Contao2BackendView/ActionHandler/ParentedListViewShowAllHandler.php
index 8e18809da..a8dc4408c 100644
--- a/src/Contao/View/Contao2BackendView/ActionHandler/ParentedListViewShowAllHandler.php
+++ b/src/Contao/View/Contao2BackendView/ActionHandler/ParentedListViewShowAllHandler.php
@@ -576,7 +576,7 @@ private function getGrandParentId(
         $grandParentProvider = $environment->getDataProvider($grandParentName);
 
         $config = $grandParentProvider->getEmptyConfig();
-        $config->setFilter($relationship->getInverseFilterFor($parentModel));
+        $config->setFilter((array) $relationship->getInverseFilterFor($parentModel));
 
         $parents = $grandParentProvider->fetchAll($config);
 
diff --git a/src/Contao/View/Contao2BackendView/ButtonRenderer.php b/src/Contao/View/Contao2BackendView/ButtonRenderer.php
index 875c80e5a..ef5190f00 100644
--- a/src/Contao/View/Contao2BackendView/ButtonRenderer.php
+++ b/src/Contao/View/Contao2BackendView/ButtonRenderer.php
@@ -4,6 +4,7 @@
  * This file is part of contao-community-alliance/dc-general.
  *
  * (c) 2013-2021 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,7 +17,8 @@
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
  * @author     Richard Henkenjohann <richardhenkenjohann@googlemail.com>
- * @copyright  2013-2021 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -124,13 +126,10 @@ public function __construct(EnvironmentInterface $environment)
         $this->circularModelIds = [];
 
         // We must only check for CUT operation here as pasting copy'ed parents is allowed.
-        $cutItems  = \array_filter(
-            $this->clipboardItems,
-            function ($item) {
-                /** @var ItemInterface $item */
-                return $item->getAction() === $item::CUT;
-            }
-        );
+        $cutItems  = \array_filter($this->clipboardItems, function ($item) {
+            /** @var ItemInterface $item */
+            return $item->getAction() === $item::CUT;
+        });
         $cutModels = $controller->getModelsFromClipboardItems($cutItems);
         $collector = new ModelCollector($environment);
         foreach ($cutModels as $model) {
diff --git a/src/Contao/View/Contao2BackendView/Subscriber/WidgetBuilder.php b/src/Contao/View/Contao2BackendView/Subscriber/WidgetBuilder.php
index af2913813..f18ee719c 100644
--- a/src/Contao/View/Contao2BackendView/Subscriber/WidgetBuilder.php
+++ b/src/Contao/View/Contao2BackendView/Subscriber/WidgetBuilder.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2021 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,7 +16,7 @@
  * @author     Stefan Heimes <stefan_heimes@hotmail.com>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Richard Henkenjohann <richardhenkenjohann@googlemail.com>
- * @copyright  2013-2021 Contao Community Alliance.
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -483,9 +483,6 @@ private function prepareWidgetAttributes(ModelInterface $model, PropertyInterfac
             ],
             'options'   => $this->getOptionsForWidget($property, $model),
             'eval'      => $propExtra,
-            // @codingStandardsIgnoreStart
-            // 'foreignKey' => null
-            // @codingStandardsIgnoreEnd
         ];
 
         if (isset($propExtra['reference'])) {
diff --git a/src/Contao/View/Contao2BackendView/TreePicker.php b/src/Contao/View/Contao2BackendView/TreePicker.php
index f8bcd3b09..0e4eaada4 100644
--- a/src/Contao/View/Contao2BackendView/TreePicker.php
+++ b/src/Contao/View/Contao2BackendView/TreePicker.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2021 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,7 +16,9 @@
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Richard Henkenjohann <richardhenkenjohann@googlemail.com>
- * @copyright  2013-2021 Contao Community Alliance.
+ * @author     Ingolf Steinhardt <info@e-spin.de>
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
diff --git a/src/Contao/View/Contao2BackendView/Widget/FileTree.php b/src/Contao/View/Contao2BackendView/Widget/FileTree.php
index c337e0634..ba5791b8d 100644
--- a/src/Contao/View/Contao2BackendView/Widget/FileTree.php
+++ b/src/Contao/View/Contao2BackendView/Widget/FileTree.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2021 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,7 +16,7 @@
  * @author     Stefan Heimes <stefan_heimes@hotmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2021 Contao Community Alliance.
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -370,19 +370,20 @@ protected function renderIcon($model, $imagesOnly = false, $downloads = false)
             return Image::getHtml($file->icon) . ' ' . $info;
         }
 
-        return $this->generateGalleryImage($model, $file, $info);
+        return $this->generateGalleryImage($file, $info);
     }
 
     /**
      * Generate an image for use as gallery listing.
      *
-     * @param FilesModel $model The file model in use.
      * @param File       $file  The image file being rendered.
      * @param string     $info  The image information.
      *
      * @return string
+     *
+     * @SuppressWarnings(PHPMD.CyclomaticComplexity)
      */
-    private function generateGalleryImage($model, File $file, $info)
+    private function generateGalleryImage(File $file, $info)
     {
         if ($file->viewWidth && $file->viewHeight
             && ($file->isSvgImage
diff --git a/src/Controller/ModelCollector.php b/src/Controller/ModelCollector.php
index 840c5e767..e95c5eb88 100644
--- a/src/Controller/ModelCollector.php
+++ b/src/Controller/ModelCollector.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2020 Contao Community Alliance.
+ * (c) 2013-2021 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -14,7 +14,8 @@
  * @author     Christian Schiffler <c.schiffler@cyberspectrum.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2021 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -96,6 +97,13 @@ class ModelCollector
      */
     private $parentProviderName;
 
+    /**
+     * The default data provider name.
+     *
+     * @var string
+     */
+    private $defaultProviderName;
+
     /**
      * Create a new instance.
      *
@@ -120,6 +128,11 @@ public function __construct(EnvironmentInterface $environment)
             if (!$this->rootCondition instanceof RootConditionInterface) {
                 throw new DcGeneralRuntimeException('No root condition specified for hierarchical mode.');
             }
+
+            if ($this->environment->getParentDataDefinition()) {
+                $this->parentProviderName = $basicDefinition->getParentDataProvider();
+                $this->parentProvider     = $this->environment->getDataProvider($this->parentProviderName);
+            }
         }
         if (BasicDefinitionInterface::MODE_PARENTEDLIST === $this->definitionMode) {
             $this->parentProviderName = $basicDefinition->getParentDataProvider();
@@ -196,12 +209,17 @@ public function getModel($modelId, $providerName = null)
      * @param ModelInterface      $model  The model to search the parent for.
      * @param CollectionInterface $models The collection to search in.
      *
-     * @return ModelInterface
+     * @return ModelInterface|null
+     *
+     * @throws DcGeneralInvalidArgumentException When the model does not originate from the child provider.
      */
     public function searchParentOfIn(ModelInterface $model, CollectionInterface $models)
     {
+        $this->guardModelOriginatesFromProvider($model);
+
         foreach ($models as $candidate) {
             /** @var ModelInterface $candidate */
+
             foreach ($this->relationships->getChildConditions($candidate->getProviderName()) as $condition) {
                 if ($condition->matches($candidate, $model)) {
                     return $candidate;
@@ -222,11 +240,15 @@ public function searchParentOfIn(ModelInterface $model, CollectionInterface $mod
     /**
      * Search the parent model for the given model.
      *
+     * If the model is part of a hierarchical structure the parent node is determined instead of a possible available
+     * parent relationship.
+     *
      * @param ModelInterface $model The model for which the parent shall be retrieved.
      *
      * @return ModelInterface|null
      *
      * @throws DcGeneralInvalidArgumentException When a root model has been passed or not in hierarchical mode.
+     * @throws DcGeneralInvalidArgumentException When the model does not originate from the child provider.
      */
     public function searchParentOf(ModelInterface $model)
     {
@@ -386,17 +408,13 @@ private function internalCollectChildrenOf(ModelInterface $model, $providerName
      */
     private function searchParentOfInParentedMode(ModelInterface $model)
     {
-        if ($this->defaultProviderName !== $model->getProviderName()) {
-            throw new DcGeneralInvalidArgumentException(
-                'Model originates from ' . $model->getProviderName() .
-                ' but is expected to be from ' . $this->defaultProviderName .
-                ' can not determine parent.'
-            );
-        }
+        $this->guardParentProviderDefined();
 
         $condition = $this->relationships->getChildCondition($this->parentProviderName, $this->defaultProviderName);
-        // This is pretty expensive, we fetch all models from the parent provider here.
-        // This can be much faster by using the inverse condition if present.
+        if (null !== ($inverseFilter = $condition->getInverseFilterFor($model))) {
+            return $this->parentProvider->fetch($this->parentProvider->getEmptyConfig()->setFilter($inverseFilter));
+        }
+
         foreach ($this->parentProvider->fetchAll($this->parentProvider->getEmptyConfig()) as $candidate) {
             if ($condition->matches($candidate, $model)) {
                 return $candidate;
@@ -412,16 +430,30 @@ private function searchParentOfInParentedMode(ModelInterface $model)
      * @param ModelInterface $model The model to search the parent of.
      *
      * @return ModelInterface|null
-     *
-     * @throws DcGeneralInvalidArgumentException When a root model has been passed.
      */
     private function searchParentOfInHierarchical(ModelInterface $model)
     {
-        if ($this->isRootModel($model)) {
-            throw new DcGeneralInvalidArgumentException('Invalid condition, root models can not have parents!');
+        $this->guardRootProviderDefined();
+
+        foreach ($this->relationships->getChildConditions() as $condition) {
+            // Skip conditions where the destination is not the provider
+            if ($this->defaultProviderName !== $condition->getDestinationName()) {
+                continue;
+            }
+
+            if (null === ($inverseFilter = $condition->getInverseFilterFor($model))) {
+                continue;
+            }
+
+            $provider = $this->environment->getDataProvider($condition->getSourceName());
+            $config   = $provider->getEmptyConfig()->setFilter($inverseFilter);
+            $parent   = $this->environment->getDataProvider($condition->getSourceName())->fetch($config);
+
+            if (null !== $parent) {
+                return $parent;
+            }
         }
-        // Start from the root data provider and walk through the whole tree.
-        // To speed up, some conditions have an inverse filter - we should use them!
+
         $config = $this->rootProvider->getEmptyConfig()->setFilter($this->rootCondition->getFilterArray());
 
         return $this->searchParentOfIn($model, $this->rootProvider->fetchAll($config));
@@ -475,4 +507,58 @@ private function isRootModel(ModelInterface $model)
     {
         return (null !== $this->rootCondition) && $this->rootCondition->matches($model);
     }
+
+    /**
+     * Guards that a root provider is defined.
+     *
+     * @return void
+     *
+     * @throws DcGeneralInvalidArgumentException When not root provider is defined.
+     */
+    private function guardRootProviderDefined(): void
+    {
+        if (null === $this->rootProvider) {
+            throw new DcGeneralInvalidArgumentException(
+                'Invalid configuration. The root data provider must be defined!'
+            );
+        }
+    }
+
+    /**
+     * Guards that a parent provider is defined.
+     *
+     * @return void
+     *
+     * @throws DcGeneralInvalidArgumentException When not root provider is defined.
+     */
+    private function guardParentProviderDefined(): void
+    {
+        if (null === $this->parentProvider) {
+            throw new DcGeneralInvalidArgumentException(
+                'Invalid configuration. The parent data provider must be defined!'
+            );
+        }
+    }
+
+    /**
+     * This guard checks if the model belongs to the configured data provider.
+     *
+     * @param ModelInterface $model The model to check.
+     *
+     * @return void
+     *
+     * @throws DcGeneralInvalidArgumentException When model is not for the configured provider.
+     */
+    private function guardModelOriginatesFromProvider(ModelInterface $model): void
+    {
+        if ($this->defaultProviderName === $model->getProviderName()) {
+            return;
+        }
+
+        throw new DcGeneralInvalidArgumentException(
+            'Model originates from ' . $model->getProviderName() .
+            ' but is expected to be from ' . $this->defaultProviderName .
+            ' can not determine parent.'
+        );
+    }
 }
diff --git a/src/DataDefinition/ModelRelationship/ParentChildCondition.php b/src/DataDefinition/ModelRelationship/ParentChildCondition.php
index 6eaa72d95..ebc95f97d 100644
--- a/src/DataDefinition/ModelRelationship/ParentChildCondition.php
+++ b/src/DataDefinition/ModelRelationship/ParentChildCondition.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2021 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -15,7 +15,8 @@
  * @author     Stefan Heimes <stefan_heimes@hotmail.com>
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2021 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -352,6 +353,10 @@ public function getInverseFilterFor($child)
             $result[] = $applied;
         }
 
+        if ([] === $result) {
+            return null;
+        }
+
         return $result;
     }
 
diff --git a/src/DataDefinition/Palette/Condition/Property/DumpingPropertyCondition.php b/src/DataDefinition/Palette/Condition/Property/DumpingPropertyCondition.php
index c836dea3a..2cb7b546a 100644
--- a/src/DataDefinition/Palette/Condition/Property/DumpingPropertyCondition.php
+++ b/src/DataDefinition/Palette/Condition/Property/DumpingPropertyCondition.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -14,7 +14,8 @@
  * @author     Christian Schiffler <c.schiffler@cyberspectrum.de>
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -52,6 +53,8 @@ public function __construct($propertyCondition)
 
     /**
      * {@inheritdoc}
+     *
+     * @SuppressWarnings(PHPMD.DevelopmentCodeFragment)
      */
     public function match(
         ModelInterface $model = null,
diff --git a/src/Resources/contao/config/config.php b/src/Resources/contao/config/config.php
index 35b4a45fe..f80d7599d 100644
--- a/src/Resources/contao/config/config.php
+++ b/src/Resources/contao/config/config.php
@@ -1,12 +1,9 @@
 <?php
 
-use ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Widget\FileTree;
-use ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\TreePicker;
-
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -19,17 +16,19 @@
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Andreas Isaak <andy.jared@googlemail.com>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
 
-/**
- * JS
- */
+use ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Widget\FileTree;
+use ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\TreePicker;
+
+// JS
 if (defined('TL_MODE') && TL_MODE === 'BE') {
     $GLOBALS['TL_JAVASCRIPT']['cca.dc-general.generalDriver_src'] = 'bundles/ccadcgeneral/js/generalDriver_src.js';
-    $GLOBALS['TL_JAVASCRIPT']['cca.dc-general.vanillaGeneral'] = 'bundles/ccadcgeneral/js/vanillaGeneral.js';
+    $GLOBALS['TL_JAVASCRIPT']['cca.dc-general.vanillaGeneral']    = 'bundles/ccadcgeneral/js/vanillaGeneral.js';
 }
 
 $GLOBALS['BE_FFL']['DcGeneralTreePicker'] = TreePicker::class;
diff --git a/src/Resources/contao/languages/de/default.php b/src/Resources/contao/languages/de/default.php
index ac80ae63f..31901e7e8 100644
--- a/src/Resources/contao/languages/de/default.php
+++ b/src/Resources/contao/languages/de/default.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2020 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,11 +16,13 @@
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
- * @copyright  2013-2020 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
 
+// @codingStandardsIgnoreStart
 $GLOBALS['TL_LANG']['MSC']['language']                    = 'Sprache';
 $GLOBALS['TL_LANG']['MSC']['showSelected']                = 'Sprache wechseln';
 $GLOBALS['TL_LANG']['MSC']['treePicker']                  = 'Tabelle: %s';
@@ -37,3 +39,4 @@
 $GLOBALS['TL_LANG']['MSC']['no_properties_available']     = 'Bitte überprüfen Sie die ausgewählten Eigenschaften!';
 $GLOBALS['TL_LANG']['MSC']['select_models']               = 'Elemente auswählen';
 $GLOBALS['TL_LANG']['MSC']['dc_general_disabled']         = 'Gesperrt: %s';
+// @codingStandardsIgnoreEnd
diff --git a/src/Resources/contao/languages/en/default.php b/src/Resources/contao/languages/en/default.php
index 0583e002e..928eb9205 100644
--- a/src/Resources/contao/languages/en/default.php
+++ b/src/Resources/contao/languages/en/default.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2020 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -16,11 +16,13 @@
  * @author     Tristan Lins <tristan.lins@bit3.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Ingolf Steinhardt <info@e-spin.de>
- * @copyright  2013-2020 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
 
+// @codingStandardsIgnoreStart
 $GLOBALS['TL_LANG']['MSC']['language']                    = 'Language';
 $GLOBALS['TL_LANG']['MSC']['showSelected']                = 'Switch language';
 $GLOBALS['TL_LANG']['MSC']['treePicker']                  = 'Table: %s';
@@ -37,3 +39,4 @@
 $GLOBALS['TL_LANG']['MSC']['no_properties_available']     = 'Please check your selected properties!';
 $GLOBALS['TL_LANG']['MSC']['select_models']               = 'Select models';
 $GLOBALS['TL_LANG']['MSC']['dc_general_disabled']         = 'Disabled: %s';
+// @codingStandardsIgnoreEnd
diff --git a/src/deprecated-autoload.php b/src/deprecated-autoload.php
index 32a9f7c78..9eedacc46 100644
--- a/src/deprecated-autoload.php
+++ b/src/deprecated-autoload.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2022 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -13,7 +13,8 @@
  * @package    contao-community-alliance/dc-general
  * @author     Sven Baumann <baumann.sv@gmail.com>
  * @author     Richard Henkenjohann <richardhenkenjohann@googlemail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2022 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -28,11 +29,13 @@
 spl_autoload_register(
     function ($class) {
         static $classes = [
+            // @codingStandardsIgnoreStart Line exceeds 120 characters
             '\ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Exception\DefinitionException'          => DefinitionException::class,
             '\ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Exception\EditOnlyModeException'        => EditOnlyModeException::class,
             '\ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Exception\NotCreatableException'        => NotCreatableException::class,
             '\ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Exception\NotDeletableException'        => NotDeletableException::class,
             '\ContaoCommunityAlliance\DcGeneral\Contao\View\Contao2BackendView\Subscriber\ColorPickerWizardSubscriber' => ColorPickerWizardListener::class,
+            // @codingStandardsIgnoreEnd
         ];
 
         if (isset($classes[$class])) {
diff --git a/tests/Controller/ModelCollectorTest.php b/tests/Controller/ModelCollectorTest.php
index cae05711c..a4b31e09d 100644
--- a/tests/Controller/ModelCollectorTest.php
+++ b/tests/Controller/ModelCollectorTest.php
@@ -3,7 +3,7 @@
 /**
  * This file is part of contao-community-alliance/dc-general.
  *
- * (c) 2013-2019 Contao Community Alliance.
+ * (c) 2013-2021 Contao Community Alliance.
  *
  * For the full copyright and license information, please view the LICENSE
  * file that was distributed with this source code.
@@ -13,7 +13,8 @@
  * @package    contao-community-alliance/dc-general
  * @author     Christian Schiffler <c.schiffler@cyberspectrum.de>
  * @author     Sven Baumann <baumann.sv@gmail.com>
- * @copyright  2013-2019 Contao Community Alliance.
+ * @author     David Molineus <david.molineus@netzmacht.de>
+ * @copyright  2013-2021 Contao Community Alliance.
  * @license    https://github.com/contao-community-alliance/dc-general/blob/master/LICENSE LGPL-3.0-or-later
  * @filesource
  */
@@ -25,6 +26,8 @@
 use ContaoCommunityAlliance\DcGeneral\Data\CollectionInterface;
 use ContaoCommunityAlliance\DcGeneral\Data\ConfigInterface;
 use ContaoCommunityAlliance\DcGeneral\Data\DataProviderInterface;
+use ContaoCommunityAlliance\DcGeneral\Data\DefaultCollection;
+use ContaoCommunityAlliance\DcGeneral\Data\DefaultModel;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelId;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelIdInterface;
 use ContaoCommunityAlliance\DcGeneral\Data\ModelInterface;
@@ -32,10 +35,13 @@
 use ContaoCommunityAlliance\DcGeneral\DataDefinition\Definition\BasicDefinitionInterface;
 use ContaoCommunityAlliance\DcGeneral\DataDefinition\Definition\ModelRelationshipDefinitionInterface;
 use ContaoCommunityAlliance\DcGeneral\DataDefinition\Definition\PropertiesDefinitionInterface;
+use ContaoCommunityAlliance\DcGeneral\DataDefinition\ModelRelationship\ParentChildCondition;
+use ContaoCommunityAlliance\DcGeneral\DataDefinition\ModelRelationship\ParentChildConditionInterface;
 use ContaoCommunityAlliance\DcGeneral\DataDefinition\ModelRelationship\RootConditionInterface;
 use ContaoCommunityAlliance\DcGeneral\EnvironmentInterface;
 use ContaoCommunityAlliance\DcGeneral\Exception\DcGeneralRuntimeException;
 use ContaoCommunityAlliance\DcGeneral\Test\TestCase;
+use Generator;
 
 /**
  * Test case for the relationship manager.
@@ -208,6 +214,328 @@ public function testCollectSiblingsOf()
         self::assertSame($collection, $collector->collectSiblingsOf($model));
     }
 
+    /**
+     * Provides data for the testSearchParentOfInWithoutRecursion test.
+     *
+     * @return Generator
+     */
+    public function provideForTestSearchParentOfInWithoutRecursion(): Generator
+    {
+        $collection = new DefaultCollection();
+        $collection->push($parentA = $this->createModel('parent', 1));
+        $collection->push($parentB = $this->createModel('parent', 2));
+
+        yield [
+            $parentB,
+            $this->createModel('child', 1, ['pid' => 2]),
+            $collection,
+        ];
+
+        yield [
+            $parentA,
+            $this->createModel('child', 1, ['pid' => 1]),
+            $collection
+        ];
+
+        yield [
+            null,
+            $this->createModel('child', 1, ['pid' => 3]),
+            $collection
+        ];
+    }
+
+    /**
+     * Tests the searchParentOfIn method without recursion.
+     *
+     * @param ModelInterface|null             $expected   The expected parent.
+     * @param ModelInterface                  $model      The given instance of the model.
+     * @param CollectionInterface             $candidates The given candidates of the parent for the model.
+     *
+     * @return void
+     *
+     * @dataProvider provideForTestSearchParentOfInWithoutRecursion
+     */
+    public function testSearchParentOfInWithoutRecursion(
+        ?ModelInterface $expected,
+        ModelInterface $model,
+        CollectionInterface $candidates
+    ): void {
+        $definition = $this->mockDefinitionContainer();
+
+        $basicDefinition = $this->mockBasicDefinition();
+        $basicDefinition->method('getDataProvider')->willReturn('child');
+        $basicDefinition->method('getParentDataProvider')->willReturn('parent');
+        $basicDefinition->method('getMode')->willReturn(BasicDefinitionInterface::MODE_PARENTEDLIST);
+        $definition->method('getBasicDefinition')->willReturn($basicDefinition);
+
+        $relationships = $this->mockRelationshipDefinition();
+        $conditions    = [$this->createParentChildCondition('parent', 'child')];
+        $relationships->method('getChildConditions')->willReturn($conditions);
+        $definition->method('getModelRelationshipDefinition')->willReturn($relationships);
+
+        $environment = $this->getMockForAbstractClass(EnvironmentInterface::class);
+        $environment->method('getDataDefinition')->willReturn($definition);
+
+        $config = $this->getMockForAbstractClass(ConfigInterface::class);
+        $config
+            ->method('setFilter')
+            ->willReturn($config);
+
+        $parentProvider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $parentProvider->method('getEmptyConfig')->willReturn($config);
+        $parentProvider->method('fetchAll')->with($config)->willReturn(new DefaultCollection());
+
+        $provider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $provider->method('getEmptyConfig')->willReturn($config);
+        $provider->method('fetchAll')->with($config)->willReturn(new DefaultCollection());
+
+        $environment->method('getDataProvider')->willReturnCallback(
+            function (string $name) use ($provider, $parentProvider) {
+                switch ($name) {
+                    case 'child':
+                        return $provider;
+                    case 'parent':
+                        return $parentProvider;
+
+                    default:
+                        throw new \RuntimeException();
+                }
+            }
+        );
+
+        $collector = new ModelCollector($environment);
+
+        self::assertSame($expected, $collector->searchParentOfIn($model, $candidates));
+    }
+
+    /**
+     * Provides data for the testSearchParentOfWithRecursion test.
+     *
+     * @return Generator
+     */
+    public function provideForTestSearchParentOfInWithRecursion(): Generator
+    {
+        $parents = new DefaultCollection();
+        $parents->push($parentA = $this->createModel('parent', 1, ['pid' => 10]));
+        $parents->push($parentB = $this->createModel('parent', 2, ['pid' => 11]));
+
+        $grandParents = new DefaultCollection();
+        $grandParents->push($this->createModel('grandparent', 10));
+        $grandParents->push($this->createModel('grandparent', 11));
+
+        yield [
+            $parentB,
+            $this->createModel('child', 1, ['pid' => 2]),
+            $parents,
+            $grandParents,
+        ];
+
+        yield [
+            $parentA,
+            $this->createModel('child', 1, ['pid' => 1]),
+            $parents,
+            $grandParents,
+        ];
+
+        yield [
+            null,
+            $this->createModel('child', 1, ['pid' => 3]),
+            $parents,
+            $grandParents,
+        ];
+    }
+
+    /**
+     * Tests the searchParentOfIn method without recursion.
+     *
+     * @param ModelInterface|null $expected     The expected parent.
+     * @param ModelInterface      $model        The given instance of the model.
+     * @param CollectionInterface $parents      The given candidates of the parent for the model.
+     * @param CollectionInterface $grandParents The given candidates of the parent for the model.
+     *
+     * @return void
+     *
+     * @dataProvider provideForTestSearchParentOfInWithRecursion
+     */
+    public function testSearchParentOfInWithRecursion(
+        ?ModelInterface $expected,
+        ModelInterface $model,
+        CollectionInterface $parents,
+        CollectionInterface $grandParents
+    ): void {
+        $definition      = $this->mockDefinitionContainer();
+        $basicDefinition = $this->mockBasicDefinition();
+        $basicDefinition->method('getDataProvider')->willReturn('child');
+        $basicDefinition->method('getParentDataProvider')->willReturn('parent');
+        $basicDefinition->method('getMode')->willReturn(BasicDefinitionInterface::MODE_PARENTEDLIST);
+        $definition->method('getBasicDefinition')->willReturn($basicDefinition);
+
+        $relationships = $this->mockRelationshipDefinition();
+        $relationships->method('getChildConditions')->willReturnCallback(
+            function (string $providerName): array {
+                switch ($providerName) {
+                    case 'grandparent':
+                        return [$this->createParentChildCondition('grandparent', 'parent')];
+
+                    case  'parent':
+                        return [$this->createParentChildCondition('parent', 'child')];
+
+                    default:
+                        throw new \RuntimeException();
+                }
+            }
+        );
+
+        $definition->method('getModelRelationshipDefinition')->willReturn($relationships);
+
+        $environment = $this->getMockForAbstractClass(EnvironmentInterface::class);
+        $environment->method('getDataDefinition')->willReturn($definition);
+
+        $config = $this->getMockForAbstractClass(ConfigInterface::class);
+        $config
+            ->method('setFilter')
+            ->willReturn($config);
+
+        $parentProvider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $parentProvider->method('getEmptyConfig')->willReturn($config);
+        $parentProvider->method('fetchAll')->with($config)->willReturn($parents);
+
+        $config = $this->getMockForAbstractClass(ConfigInterface::class);
+        $config
+            ->method('setFilter')
+            ->willReturn($config);
+
+        $grandParentProvider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $grandParentProvider->method('getEmptyConfig')->willReturn($config);
+        $grandParentProvider->method('fetchAll')->with($config)->willReturn(new DefaultCollection());
+
+        $provider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $provider->method('getEmptyConfig')->willReturn($config);
+        $provider->method('fetchAll')->with($config)->willReturn(new DefaultCollection());
+
+        $environment->method('getDataProvider')->willReturnCallback(
+            function (string $name) use ($provider, $parentProvider, $grandParentProvider) {
+                switch ($name) {
+                    case 'child':
+                        return $provider;
+                    case 'parent':
+                        return $parentProvider;
+                    case 'grandparent':
+                        return $grandParentProvider;
+
+                    default:
+                        throw new \RuntimeException();
+                }
+            }
+        );
+
+        $collector = new ModelCollector($environment);
+        self::assertSame($expected, $collector->searchParentOfIn($model, $grandParents));
+    }
+
+    /**
+     * Provides data for the testSearchParentOfInHierarchical test.
+     *
+     * @return Generator
+     */
+    public function provideForTestSearchParentOfInHierarchicalByInverseFilter(): Generator
+    {
+        $parentNodeA = $this->createModel('node', 10);
+        $parentNodeB = $this->createModel('node', 11);
+
+        yield [
+            $parentNodeA,
+            $this->createModel('node', 1, ['pid' => 10, 'parentId' => 1]),
+        ];
+
+        yield [
+            $parentNodeB,
+            $this->createModel('node', 1, ['pid' => 11, 'parentId' => 2]),
+        ];
+
+        yield [
+            null,
+            $this->createModel('node', 1, ['pid' => 12, 'parentId' => 1]),
+        ];
+    }
+
+    /**
+     * Tests the searchParentOfIn method without recursion.
+     *
+     * @param ModelInterface|null $expected The expected parent.
+     * @param ModelInterface      $model    The given instance of the model.
+     *
+     * @return void
+     *
+     * @dataProvider provideForTestSearchParentOfInHierarchicalByInverseFilter
+     */
+    public function testSearchParentOfInHierarchicalByInverseFilter(
+        ?ModelInterface $expected,
+        ModelInterface $model
+    ): void {
+        $definition      = $this->mockDefinitionContainer();
+        $basicDefinition = $this->mockBasicDefinition();
+        $basicDefinition->method('getDataProvider')->willReturn('node');
+        $basicDefinition->method('getRootDataProvider')->willReturn('node');
+        $basicDefinition->method('getParentDataProvider')->willReturn('parent');
+        $basicDefinition->method('getMode')->willReturn(BasicDefinitionInterface::MODE_HIERARCHICAL);
+        $definition->method('getBasicDefinition')->willReturn($basicDefinition);
+
+        $relationships = $this->mockRelationshipDefinition();
+        $relationships->method('getChildConditions')->willReturn(
+            [
+                $this->createParentChildCondition('parent', 'node'),
+                $this->createParentChildCondition('node', 'node'),
+            ]
+        );
+
+        $rootCondition = $this->getMockForAbstractClass(RootConditionInterface::class);
+        $relationships->method('getRootCondition')->willReturn($rootCondition);
+
+        $definition->method('getModelRelationshipDefinition')->willReturn($relationships);
+
+        $environment = $this->getMockForAbstractClass(EnvironmentInterface::class);
+        $environment->method('getDataDefinition')->willReturn($definition);
+
+        $config = $this->getMockForAbstractClass(ConfigInterface::class);
+        $config->method('setFilter')->willReturn($config);
+
+        $parentProvider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $parentProvider->method('getEmptyConfig')->willReturn($config);
+        $parentProvider
+            ->expects($this->once())
+            ->method('fetch')
+            ->willReturn(null);
+
+        $provider = $this->getMockForAbstractClass(DataProviderInterface::class);
+        $provider->method('getEmptyConfig')->willReturn($config);
+        $provider
+            ->expects($this->once())
+            ->method('fetch')->willReturn($expected);
+
+        $provider
+            ->expects(null === $expected ? $this->once() : $this->never())
+            ->method('fetchAll')
+            ->willReturn(new DefaultCollection());
+
+        $environment->method('getDataProvider')->willReturnCallback(
+            function (string $name) use ($provider, $parentProvider) {
+                switch ($name) {
+                    case 'node':
+                        return $provider;
+                    case 'parent':
+                        return $parentProvider;
+
+                    default:
+                        throw new \RuntimeException();
+                }
+            }
+        );
+
+        $collector = new ModelCollector($environment);
+        self::assertSame($expected, $collector->searchParentOf($model));
+    }
+
     /**
      * Mock a basic definition.
      *
@@ -247,4 +575,52 @@ private function mockPropertiesDefinition()
     {
         return $this->getMockForAbstractClass(PropertiesDefinitionInterface::class);
     }
+
+    private function createModel(string $providerName, int $id, array $properties = []): ModelInterface
+    {
+        $model = new DefaultModel();
+        $model->setID($id);
+        $model->setProviderName($providerName);
+        $model->setPropertiesAsArray($properties);
+
+        return $model;
+    }
+
+    private function createParentChildCondition(
+        string $sourceName,
+        string $destinationName
+    ): ParentChildConditionInterface {
+        $condition  = new ParentChildCondition();
+        $condition->setSourceName($sourceName);
+        $condition->setDestinationName($destinationName);
+        $condition->setSetters(
+            [
+                [
+                    'to_field'   => 'pid',
+                    'from_field' => 'id',
+                ],
+            ]
+        );
+        $condition->setInverseFilterArray(
+            [
+                [
+                    'local'     => 'pid',
+                    'remote'    => 'id',
+                    'operation' => '=',
+                ],
+            ]
+        );
+
+        $condition->setFilterArray(
+            [
+                [
+                    'local'     => 'pid',
+                    'remote'    => 'id',
+                    'operation' => '=',
+                ],
+            ]
+        );
+
+        return $condition;
+    }
 }