diff --git a/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaveProcessor.php b/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaveProcessor.php
new file mode 100644
index 0000000000..4a2996ad0d
--- /dev/null
+++ b/application/Espo/Core/FieldProcessing/Relation/LinkMultipleSaveProcessor.php
@@ -0,0 +1,199 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\FieldProcessing\Relation;
+
+use Espo\Core\{
+    ORM\Entity,
+    ORM\EntityManager,
+};
+
+class LinkMultipleSaveProcessor
+{
+    private $entityManager;
+
+    public function __construct(EntityManager $entityManager)
+    {
+        $this->entityManager = $entityManager;
+    }
+
+    public function process(Entity $entity, string $name, array $options): void
+    {
+        $entityType = $entity->getEntityType();
+
+        $repository = $this->entityManager->getRDBRepository($entityType);
+
+        $idListAttribute = $name . 'Ids';
+        $columnsAttribute = $name . 'Columns';
+
+        $defs = $this->entityManager->getDefs()->getEntity($entityType);
+
+        $skipCreate = $options['skipLinkMultipleCreate'] ?? false;
+        $skipRemove = $options['skipLinkMultipleRemove'] ?? false;
+        $skipUpdate = $options['skipLinkMultipleUpdate'] ?? false;
+
+        if ($entity->isNew()) {
+            $skipRemove = true;
+            $skipUpdate = true;
+        }
+
+        if ($entity->has($idListAttribute)) {
+            $specifiedIdList = $entity->get($idListAttribute);
+        }
+        else if ($entity->has($columnsAttribute)) {
+            $skipRemove = true;
+
+            $specifiedIdList = array_keys(
+                get_object_vars(
+                    $entity->get($columnsAttribute) ?? (object) []
+                )
+            );
+        }
+        else {
+            return;
+        }
+
+        if (!is_array($specifiedIdList)) {
+            return;
+        }
+
+        $toRemoveIdList = [];
+        $existingIdList = [];
+        $toUpdateIdList = [];
+        $toCreateIdList = [];
+
+        $existingColumnsData = (object) [];
+
+        $columns = null;
+
+        if ($defs->hasField($name)) {
+            $columns = $defs->getField($name)->getParam('columns');
+        }
+
+        $columnData = !empty($columns) ?
+            $entity->get($columnsAttribute) :
+            null;
+
+        if (!$skipRemove || !$skipUpdate) {
+            $foreignEntityList = $repository->getRelation($entity, $name)->find();
+
+            foreach ($foreignEntityList as $foreignEntity) {
+                $existingIdList[] = $foreignEntity->id;
+
+                if (empty($columns)) {
+                    continue;
+                }
+
+                $data = (object) [];
+
+                foreach ($columns as $columnName => $columnField) {
+                    $foreignId = $foreignEntity->id;
+
+                    $data->$columnName = $foreignEntity->get($columnField);
+                }
+
+                $existingColumnsData->$foreignId = $data;
+
+                if (!$entity->isNew()) {
+                    $entity->setFetched($columnsAttribute, $existingColumnsData);
+                }
+            }
+        }
+
+        if (!$entity->isNew()) {
+            if ($entity->has($idListAttribute) && !$entity->hasFetched($idListAttribute)) {
+                $entity->setFetched($idListAttribute, $existingIdList);
+            }
+
+            if ($entity->has($columnsAttribute) && !empty($columns)) {
+                $entity->setFetched($columnsAttribute, $existingColumnsData);
+            }
+        }
+
+        foreach ($existingIdList as $id) {
+            if (!in_array($id, $specifiedIdList)) {
+                if (!$skipRemove) {
+                    $toRemoveIdList[] = $id;
+                }
+
+                continue;
+            }
+
+            if ($skipUpdate || empty($columns)) {
+                continue;
+            }
+
+            foreach ($columns as $columnName => $columnField) {
+                if (!isset($columnData->$id) || !is_object($columnData->$id)) {
+                    continue;
+                }
+
+                if (
+                    property_exists($columnData->$id, $columnName)
+                    &&
+                    (
+                        !property_exists($existingColumnsData->$id, $columnName)
+                        ||
+                        $columnData->$id->$columnName !== $existingColumnsData->$id->$columnName
+                    )
+                ) {
+                    $toUpdateIdList[] = $id;
+                }
+            }
+        }
+
+        if (!$skipCreate) {
+            foreach ($specifiedIdList as $id) {
+                if (!in_array($id, $existingIdList)) {
+                    $toCreateIdList[] = $id;
+                }
+            }
+        }
+
+        foreach ($toCreateIdList as $id) {
+            $data = null;
+
+            if (!empty($columns) && isset($columnData->$id)) {
+                $data = (array) $columnData->$id;
+            }
+
+            $repository->getRelation($entity, $name)->relateById($id, $data);
+        }
+
+        foreach ($toRemoveIdList as $id) {
+            $repository->getRelation($entity, $name)->unrelateById($id);
+        }
+
+        foreach ($toUpdateIdList as $id) {
+            $data = (array) $columnData->$id;
+
+            $repository->getRelation($entity, $name)->updateColumnsById($id, (array) $data);
+        }
+    }
+}
diff --git a/application/Espo/Core/FieldProcessing/Relation/SaveProcessor.php b/application/Espo/Core/FieldProcessing/Relation/SaveProcessor.php
new file mode 100644
index 0000000000..2bef1e9011
--- /dev/null
+++ b/application/Espo/Core/FieldProcessing/Relation/SaveProcessor.php
@@ -0,0 +1,403 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace Espo\Core\FieldProcessing\Relation;
+
+use Espo\Core\{
+    ORM\Entity,
+    ORM\EntityManager,
+};
+
+class SaveProcessor
+{
+    private $entityManager;
+
+    private $linkMultipleSaveProcessor;
+
+    private $manyRelationListMapCache = [];
+
+    private $hasOneRelationListMapCache = [];
+
+    private $belongsToHasOneRelationListMapCache = [];
+
+    public function __construct(
+        EntityManager $entityManager,
+        LinkMultipleSaveProcessor $linkMultipleSaveProcessor
+    ) {
+        $this->entityManager = $entityManager;
+        $this->linkMultipleSaveProcessor = $linkMultipleSaveProcessor;
+    }
+
+    public function process(Entity $entity, array $options): void
+    {
+        $this->processMany($entity, $options);
+        $this->processHasOne($entity, $options);
+        $this->processBelongsToHasOne($entity, $options);
+
+        return;
+
+        foreach ($entity->getRelationList() as $name) {
+            $type = $entity->getRelationType($name);
+
+            $foreignEntityType = $entity->getRelationParam($name, 'entity');
+            $foreignKey = $entity->getRelationParam($name, 'foreignKey');
+
+            /*if (in_array($type, $manyRelationTypeList)) {
+                $idListAttribute = $name . 'Ids';
+                $columnsAttribute = $name . 'Columns';
+
+                if ($entity->has($idListAttribute) || $entity->has($columnsAttribute)) {
+                    $this->processLinkMultipleFieldSave($entity, $name, $options);
+                }
+
+                continue;
+            }*/
+
+            if ($type === $entity::HAS_ONE) {
+                /*if (!$foreignEntityType || !$foreignKey) {
+                    continue;
+                }*/
+
+                /*$noSave = $this->metadata
+                    ->get(['entityDefs', $entity->getEntityType(), 'fields', $name, 'noSave']);
+
+                if ($noSave) {
+                    continue;
+                }*/
+
+                $idAttribute = $name . 'Id';
+
+                if (!$entity->has($idAttribute)) {
+                    continue;
+                }
+
+
+                continue;
+            }
+
+            if ($type === $entity::BELONGS_TO) {
+                if (!$entity->get($name . 'Id')) {
+                    continue;
+                }
+
+                if (!$entity->isAttributeChanged($name . 'Id')) {
+                    continue;
+                }
+
+                $foreignLink = $entity->getRelationParam($name, 'foreign');
+
+                if (
+                    $this->metadata->get(
+                        ['entityDefs', $foreignEntityType, 'links', $foreignLink, 'type']
+                    ) === $entity::HAS_ONE
+                ) {
+                    $anotherEntity = $this
+                        ->select(['id'])
+                        ->where([
+                            $name . 'Id' => $entity->get($name . 'Id'),
+                            'id!=' => $entity->id,
+                        ])
+                        ->findOne();
+
+                    if ($anotherEntity) {
+                        $anotherEntity->set($name . 'Id', null);
+
+                        $this->entityManager->saveEntity($anotherEntity, [
+                            'skipAll' => true,
+                        ]);
+                    }
+                }
+
+                continue;
+            }
+        }
+    }
+
+    private function processMany(Entity $entity, array $options): void
+    {
+        $entityType = $entity->getEntityType();
+
+        foreach ($this->getManyRelationList($entityType) as $name) {
+            $this->processManyItem($entity, $name, $options);
+        }
+    }
+
+    private function processManyItem(Entity $entity, string $name, array $options): void
+    {
+        $idListAttribute = $name . 'Ids';
+        $columnsAttribute = $name . 'Columns';
+
+        if (!$entity->has($idListAttribute) && !$entity->has($columnsAttribute)) {
+            return;
+        }
+
+        $this->linkMultipleSaveProcessor->process($entity, $name, $options);
+    }
+
+    private function processHasOne(Entity $entity, array $options): void
+    {
+        $entityType = $entity->getEntityType();
+
+        foreach ($this->getHasOneRelationList($entityType) as $name) {
+            $this->processHasOneItem($entity, $name);
+        }
+    }
+
+    private function processHasOneItem(Entity $entity, string $name): void
+    {
+        $entityType = $entity->getEntityType();
+
+        $idAttribute = $name . 'Id';
+
+        if (!$entity->has($idAttribute)) {
+            return;
+        }
+
+        $id = $entity->get($idAttribute);
+
+        $defs = $this->entityManager->getDefs()->getEntity($entityType);
+
+        $relationDefs = $defs->getRelation($name);
+
+        $foreignKey = $relationDefs->getForeignKey();
+        $foreignEntityType = $relationDefs->getForeignEntityType();
+
+        $previousForeignEntity = $this->entityManager
+            ->getRDBRepository($foreignEntityType)
+            ->select(['id'])
+            ->where([
+                $foreignKey => $entity->getId(),
+            ])
+            ->findOne();
+
+        if ($previousForeignEntity) {
+            if (!$entity->isNew()) {
+                $entity->setFetched($idAttribute, $previousForeignEntity->getId());
+            }
+
+            if (!$id) {
+                $previousForeignEntity->set($foreignKey, null);
+
+                $this->entityManager->saveEntity($previousForeignEntity, [
+                    'skipAll' => true,
+                ]);
+            }
+        }
+        else if (!$entity->isNew()) {
+            $entity->setFetched($idAttribute, null);
+        }
+
+        if ($id) {
+            $this->entityManager
+                ->getRDBRepository($entityType)
+                ->getRelation($entity, $name)
+                ->relateById($id);
+        }
+    }
+
+    private function processBelongsToHasOne(Entity $entity, array $options): void
+    {
+        $entityType = $entity->getEntityType();
+
+        foreach ($this->getBelongsToHasOneRelationList($entityType) as $name) {
+            $this->processBelongsToHasOneItem($entity, $name);
+        }
+    }
+
+    private function processBelongsToHasOneItem(Entity $entity, string $name): void
+    {
+        $entityType = $entity->getEntityType();
+
+        $idAttribute = $name . 'Id';
+
+        if (!$entity->get($idAttribute)) {
+            return;
+        }
+
+        if (!$entity->isAttributeChanged($idAttribute)) {
+            return;
+        }
+
+        $anotherEntity = $this->entityManager
+            ->getRDBRepository($entityType)
+            ->select(['id'])
+            ->where([
+                $idAttribute => $entity->get($idAttribute),
+                'id!=' => $entity->getId(),
+            ])
+            ->findOne();
+
+        if (!$anotherEntity) {
+            return;
+        }
+
+        $anotherEntity->set($idAttribute, null);
+
+        $this->entityManager->saveEntity($anotherEntity, [
+            'skipAll' => true,
+        ]);
+    }
+
+    private function getManyRelationList(string $entityType): array
+    {
+        if (array_key_exists($entityType, $this->manyRelationListMapCache)) {
+            return $this->manyRelationListMapCache[$entityType];
+        }
+
+        $typeList = [
+            Entity::HAS_MANY,
+            Entity::MANY_MANY,
+            Entity::HAS_CHILDREN,
+        ];
+
+        $defs = $this->entityManager->getDefs()->getEntity($entityType);
+
+        $list = [];
+
+        foreach ($defs->getRelationNameList() as $name) {
+            $type = $defs->getRelation($name)->getType();
+
+            if (!in_array($type, $typeList)) {
+                continue;
+            }
+
+            if (!$defs->hasAttribute($name . 'Ids')) {
+                continue;
+            }
+
+            if ($defs->hasField($name) && $defs->getField($name)->getParam('noSave')) {
+                continue;
+            }
+
+            $list[] = $name;
+        }
+
+        $this->manyRelationListMapCache[$entityType] = $list;
+
+        return $list;
+    }
+
+    private function getHasOneRelationList(string $entityType): array
+    {
+        if (array_key_exists($entityType, $this->hasOneRelationListMapCache)) {
+            return $this->hasOneRelationListMapCache[$entityType];
+        }
+
+        $ormDefs = $this->entityManager->getDefs();
+
+        $defs = $ormDefs->getEntity($entityType);
+
+        $list = [];
+
+        foreach ($defs->getRelationNameList() as $name) {
+            $relationDefs = $defs->getRelation($name);
+
+            $type = $relationDefs->getType();
+
+            if ($type !== Entity::HAS_ONE) {
+                continue;
+            }
+
+            if (!$relationDefs->hasForeignEntityType()) {
+                continue;
+            }
+
+            if (!$relationDefs->hasForeignKey()) {
+                continue;
+            }
+
+            if (!$defs->hasAttribute($name . 'Id')) {
+                continue;
+            }
+
+            if ($defs->hasField($name) && $defs->getField($name)->getParam('noSave')) {
+                continue;
+            }
+
+            $list[] = $name;
+        }
+
+        $this->hasOneRelationListMapCache[$entityType] = $list;
+
+        return $list;
+    }
+
+    private function getBelongsToHasOneRelationList(string $entityType): array
+    {
+        if (array_key_exists($entityType, $this->belongsToHasOneRelationListMapCache)) {
+            return $this->belongsToHasOneRelationListMapCache[$entityType];
+        }
+
+        $ormDefs = $this->entityManager->getDefs();
+
+        $defs = $ormDefs->getEntity($entityType);
+
+        $list = [];
+
+        foreach ($defs->getRelationNameList() as $name) {
+            $relationDefs = $defs->getRelation($name);
+
+            $type = $relationDefs->getType();
+
+            if ($type !== Entity::BELONGS_TO) {
+                continue;
+            }
+
+            if (!$relationDefs->hasForeignRelationName()) {
+                continue;
+            }
+
+            if (!$relationDefs->hasForeignEntityType()) {
+                continue;
+            }
+
+            if (!$defs->hasAttribute($name . 'Id')) {
+                continue;
+            }
+
+            $foreignEntityType = $relationDefs->getForeignEntityType();
+            $foreignRelationName = $relationDefs->getForeignRelationName();
+
+            $foreignType = $ormDefs
+                ->getEntity($foreignEntityType)
+                ->getRelation($foreignRelationName)
+                ->getType();
+
+            if ($foreignType !== Entity::HAS_ONE) {
+                continue;
+            }
+
+            $list[] = $name;
+        }
+
+        $this->belongsToHasOneRelationListMapCache[$entityType] = $list;
+
+        return $list;
+    }
+}
diff --git a/application/Espo/Core/FieldProcessing/SaveProcessor.php b/application/Espo/Core/FieldProcessing/SaveProcessor.php
index 31d1f7e2d1..553c587837 100644
--- a/application/Espo/Core/FieldProcessing/SaveProcessor.php
+++ b/application/Espo/Core/FieldProcessing/SaveProcessor.php
@@ -34,6 +34,7 @@ use Espo\Core\ORM\Entity;
 use Espo\Core\{
     FieldProcessing\EmailAddress\SaveProcessor as EmailAddressSaveProcessor,
     FieldProcessing\PhoneNumber\SaveProcessor as PhoneNumberSaveProcessor,
+    FieldProcessing\Relation\SaveProcessor as RelationSaveProcessor,
 };
 
 /**
@@ -45,17 +46,22 @@ class SaveProcessor
 
     private $phoneNumberSaveProcessor;
 
+    private $relationSaveProcessor;
+
     public function __construct(
         EmailAddressSaveProcessor $emailAddressSaveProcessor,
-        PhoneNumberSaveProcessor $phoneNumberSaveProcessor
+        PhoneNumberSaveProcessor $phoneNumberSaveProcessor,
+        RelationSaveProcessor $relationSaveProcessor
     ) {
         $this->emailAddressSaveProcessor = $emailAddressSaveProcessor;
         $this->phoneNumberSaveProcessor = $phoneNumberSaveProcessor;
+        $this->relationSaveProcessor = $relationSaveProcessor;
     }
 
     public function process(Entity $entity, array $options): void
     {
         $this->emailAddressSaveProcessor->process($entity, $options);
         $this->phoneNumberSaveProcessor->process($entity, $options);
+        $this->relationSaveProcessor->process($entity, $options);
     }
 }
diff --git a/application/Espo/Core/Repositories/Database.php b/application/Espo/Core/Repositories/Database.php
index 5830225df1..0047d3f3f6 100644
--- a/application/Espo/Core/Repositories/Database.php
+++ b/application/Espo/Core/Repositories/Database.php
@@ -139,7 +139,11 @@ class Database extends RDBRepository
             ];
 
             $this->hookManager->process(
-                $this->entityType, 'afterMassRelate', $entity, $options, $hookData
+                $this->entityType,
+                'afterMassRelate',
+                $entity,
+                $options,
+                $hookData
             );
         }
     }
@@ -151,11 +155,14 @@ class Database extends RDBRepository
         if (!$this->hooksDisabled && empty($options['skipHooks'])) {
             if (is_string($foreign)) {
                 $foreignId = $foreign;
+
                 $foreignEntityType = $entity->getRelationParam($relationName, 'entity');
 
                 if ($foreignEntityType) {
                     $foreign = $this->getEntityManager()->getEntity($foreignEntityType);
-                    $foreign->id = $foreignId;
+
+                    $foreign->set('id', $foreignId);
+
                     $foreign->setAsFetched();
                 }
             }
@@ -213,7 +220,6 @@ class Database extends RDBRepository
         parent::afterSave($entity, $options);
 
         if (!$this->processFieldsAfterSaveDisabled) {
-            $this->processSpecifiedRelationsSave($entity, $options);
             $this->processFileFieldsSave($entity);
             $this->processArrayFieldsSave($entity);
             $this->processWysiwygFieldsSave($entity);
@@ -227,6 +233,7 @@ class Database extends RDBRepository
     public function save(Entity $entity, array $options = []): void
     {
         $nowString = date('Y-m-d H:i:s', time());
+
         $restoreData = [];
 
         if (
@@ -262,7 +269,8 @@ class Database extends RDBRepository
                         }
                     }
                 }
-            } else {
+            }
+            else {
                 if (empty($options['silent']) && empty($options['skipModifiedBy'])) {
                     if ($entity->hasAttribute('modifiedAt')) {
                         $entity->set('modifiedAt', $nowString);
@@ -427,275 +435,4 @@ class Database extends RDBRepository
             }
         }
     }
-
-    public function processLinkMultipleFieldSave(Entity $entity, string $link, array $options = [])
-    {
-        $name = $link;
-
-        $idListAttribute = $link . 'Ids';
-        $columnsAttribute = $link . 'Columns';
-
-        if ($this->getMetadata()->get("entityDefs." . $entity->getEntityType() . ".fields.{$name}.noSave")) {
-            return;
-        }
-
-        $skipCreate = false;
-        $skipRemove = false;
-        $skipUpdate = false;
-
-        if (!empty($options['skipLinkMultipleCreate'])) {
-            $skipCreate = true;
-        }
-
-        if (!empty($options['skipLinkMultipleRemove'])) {
-            $skipRemove = true;
-        }
-
-        if (!empty($options['skipLinkMultipleUpdate'])) {
-            $skipUpdate = true;
-        }
-
-        if ($entity->isNew()) {
-            $skipRemove = true;
-            $skipUpdate = true;
-        }
-
-        if ($entity->has($idListAttribute)) {
-            $specifiedIdList = $entity->get($idListAttribute);
-        }
-        else if ($entity->has($columnsAttribute)) {
-            $skipRemove = true;
-            $specifiedIdList = [];
-
-            foreach ($entity->get($columnsAttribute) as $id => $d) {
-                $specifiedIdList[] = $id;
-            }
-        } else {
-            return;
-        }
-
-        if (!is_array($specifiedIdList)) {
-            return;
-        }
-
-        $toRemoveIdList = [];
-        $existingIdList = [];
-        $toUpdateIdList = [];
-        $toCreateIdList = [];
-        $existingColumnsData = (object) [];
-
-        $columns = $this->getMetadata()->get(['entityDefs', $entity->getEntityType(), 'fields', $name, 'columns']);
-
-        if (!empty($columns)) {
-            $columnData = $entity->get($columnsAttribute);
-        }
-
-        if (!$skipRemove || !$skipUpdate) {
-            $foreignEntityList = $this->getRelation($entity, $name)->find();
-
-            if ($foreignEntityList) {
-                foreach ($foreignEntityList as $foreignEntity) {
-                    $existingIdList[] = $foreignEntity->id;
-
-                    if (!empty($columns)) {
-                        $data = (object) [];
-
-                        foreach ($columns as $columnName => $columnField) {
-                            $foreignId = $foreignEntity->id;
-                            $data->$columnName = $foreignEntity->get($columnField);
-                        }
-
-                        $existingColumnsData->$foreignId = $data;
-
-                        if (!$entity->isNew()) {
-                            $entity->setFetched($columnsAttribute, $existingColumnsData);
-                        }
-                    }
-                }
-            }
-        }
-
-        if (!$entity->isNew()) {
-            if ($entity->has($idListAttribute) && !$entity->hasFetched($idListAttribute)) {
-                $entity->setFetched($idListAttribute, $existingIdList);
-            }
-
-            if ($entity->has($columnsAttribute) && !empty($columns)) {
-                $entity->setFetched($columnsAttribute, $existingColumnsData);
-            }
-        }
-
-        foreach ($existingIdList as $id) {
-            if (!in_array($id, $specifiedIdList)) {
-                if (!$skipRemove) {
-                    $toRemoveIdList[] = $id;
-                }
-            }
-            else {
-                if (!$skipUpdate && !empty($columns)) {
-                    foreach ($columns as $columnName => $columnField) {
-                        if (isset($columnData->$id) && is_object($columnData->$id)) {
-                            if (
-                                property_exists($columnData->$id, $columnName)
-                                &&
-                                (
-                                    !property_exists($existingColumnsData->$id, $columnName)
-                                    ||
-                                    $columnData->$id->$columnName !== $existingColumnsData->$id->$columnName
-                                )
-                            ) {
-                                $toUpdateIdList[] = $id;
-                            }
-                        }
-                    }
-                }
-            }
-        }
-
-        if (!$skipCreate) {
-            foreach ($specifiedIdList as $id) {
-                if (!in_array($id, $existingIdList)) {
-                    $toCreateIdList[] = $id;
-                }
-            }
-        }
-
-        foreach ($toCreateIdList as $id) {
-            $data = null;
-
-            if (!empty($columns) && isset($columnData->$id)) {
-                $data = (array) $columnData->$id;
-            }
-
-            $this->getRelation($entity, $name)->relateById($id, $data);
-        }
-
-        foreach ($toRemoveIdList as $id) {
-            $this->getRelation($entity, $name)->unrelateById($id);
-        }
-
-        foreach ($toUpdateIdList as $id) {
-            $data = (array) $columnData->$id;
-
-            $this->getRelation($entity, $name)->updateColumnsById($id, (array) $data);
-        }
-    }
-
-    protected function processSpecifiedRelationsSave(Entity $entity, array $options = [])
-    {
-        $relationTypeList = [
-            $entity::HAS_MANY,
-            $entity::MANY_MANY,
-            $entity::HAS_CHILDREN,
-        ];
-
-        foreach ($entity->getRelationList() as $name) {
-
-            $type = $entity->getRelationType($name);
-
-            $foreignEntityType = $entity->getRelationParam($name, 'entity');
-            $foreignKey = $entity->getRelationParam($name, 'foreignKey');
-
-            if (in_array($type, $relationTypeList)) {
-                $idListAttribute = $name . 'Ids';
-                $columnsAttribute = $name . 'Columns';
-
-                if ($entity->has($idListAttribute) || $entity->has($columnsAttribute)) {
-                    $this->processLinkMultipleFieldSave($entity, $name, $options);
-                }
-
-                continue;
-            }
-
-            if ($type === $entity::HAS_ONE) {
-                if (!$foreignEntityType || !$foreignKey) {
-                    continue;
-                }
-
-                $noSave = $this->getMetadata()->get(
-                    ['entityDefs', $entity->getEntityType(), 'fields', $name, 'noSave']
-                );
-
-                if ($noSave) {
-                    continue;
-                }
-
-                $idAttribute = $name . 'Id';
-
-                if (!$entity->has($idAttribute)) {
-                    continue;
-                }
-
-                $where = [];
-
-                $where[$foreignKey] = $entity->id;
-
-                $previousForeignEntity = $this->getEntityManager()
-                    ->getRepository($foreignEntityType)
-                    ->select(['id'])
-                    ->where($where)
-                    ->findOne();
-
-                if ($previousForeignEntity) {
-                    if (!$entity->isNew()) {
-                        $entity->setFetched($idAttribute, $previousForeignEntity->id);
-                    }
-
-                    if (!$entity->get($idAttribute)) {
-                        $previousForeignEntity->set($foreignKey, null);
-
-                        $this->getEntityManager()->saveEntity($previousForeignEntity, ['skipAll' => true]);
-                    }
-                } else {
-                    if (!$entity->isNew()) {
-                        $entity->setFetched($idAttribute, null);
-                    }
-                }
-
-                if ($entity->get($idAttribute)) {
-                    $relateResult = $this->relate($entity, $name, $entity->get($idAttribute));
-
-                    if (!$relateResult) {
-                        $entity->set($idAttribute, null);
-                    }
-                }
-
-                continue;
-            }
-
-            if ($type === $entity::BELONGS_TO) {
-                if (!$entity->get($name . 'Id')) {
-                    continue;
-                }
-
-                if (!$entity->isAttributeChanged($name . 'Id')) {
-                    continue;
-                }
-
-                $foreignLink = $entity->getRelationParam($name, 'foreign');
-
-                if (
-                    $this->getMetadata()->get(
-                        ['entityDefs', $foreignEntityType, 'links', $foreignLink, 'type']
-                    ) === $entity::HAS_ONE
-                ) {
-                    $anotherEntity = $this
-                        ->select(['id'])
-                        ->where([
-                            $name . 'Id' => $entity->get($name . 'Id'),
-                            'id!=' => $entity->id,
-                        ])
-                        ->findOne();
-
-                    if ($anotherEntity) {
-                        $anotherEntity->set($name . 'Id', null);
-
-                        $this->getEntityManager()->saveEntity($anotherEntity, ['skipAll' => true]);
-                    }
-                }
-
-                continue;
-            }
-        }
-    }
 }
diff --git a/tests/integration/Espo/Core/FieldProcessing/RelationTest.php b/tests/integration/Espo/Core/FieldProcessing/RelationTest.php
new file mode 100644
index 0000000000..18922da98c
--- /dev/null
+++ b/tests/integration/Espo/Core/FieldProcessing/RelationTest.php
@@ -0,0 +1,192 @@
+<?php
+/************************************************************************
+ * This file is part of EspoCRM.
+ *
+ * EspoCRM - Open Source CRM application.
+ * Copyright (C) 2014-2021 Yurii Kuznietsov, Taras Machyshyn, Oleksii Avramenko
+ * Website: https://www.espocrm.com
+ *
+ * EspoCRM is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * EspoCRM is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with EspoCRM. If not, see http://www.gnu.org/licenses/.
+ *
+ * The interactive user interfaces in modified source and object code versions
+ * of this program must display Appropriate Legal Notices, as required under
+ * Section 5 of the GNU General Public License version 3.
+ *
+ * In accordance with Section 7(b) of the GNU General Public License version 3,
+ * these Appropriate Legal Notices must retain the display of the "EspoCRM" word.
+ ************************************************************************/
+
+namespace tests\integration\Espo\Core\FieldProcessing;
+
+use Espo\Core\ORM\EntityManager;
+
+class RelationTest extends \tests\integration\Core\BaseTestCase
+{
+    public function testLinkMultiple1(): void
+    {
+        /* @var $entityManager EntityManager */
+        $entityManager = $this->getContainer()->get('entityManager');
+
+        $contact1 = $entityManager->createEntity('Contact', []);
+        $contact2 = $entityManager->createEntity('Contact', []);
+        $contact3 = $entityManager->createEntity('Contact', []);
+
+        $opportunity = $entityManager->createEntity('Opportunity', [
+            'contactsIds' => [
+                $contact1->getId(),
+                $contact2->getId(),
+            ],
+            'contactsColumns' => (object) [
+                $contact1->getId() => (object) [
+                    'role' => 'Decision Maker',
+                ],
+            ],
+        ]);
+
+        $opportunity = $entityManager->getEntity('Opportunity', $opportunity->getId());
+
+        $this->assertEquals(
+            self::sortArray([
+                $contact1->getId(),
+                $contact2->getId(),
+            ]),
+            self::sortArray($opportunity->getLinkMultipleIdList('contacts'))
+        );
+
+        $column1 = $entityManager
+            ->getRDBRepository('Opportunity')
+            ->getRelation($opportunity, 'contacts')
+            ->getColumn($contact1, 'role');
+
+        $this->assertEquals('Decision Maker', $column1);
+
+        $opportunity->set([
+            'contactsIds' => [
+                $contact2->getId(),
+                $contact3->getId(),
+            ],
+            'contactsColumns' => (object) [
+                $contact2->getId() => (object) [
+                    'role' => null,
+                ],
+                $contact3->getId() => (object) [
+                    'role' => 'Evaluator',
+                ],
+            ],
+        ]);
+
+        $entityManager->saveEntity($opportunity);
+
+        $opportunity = $entityManager->getEntity('Opportunity', $opportunity->getId());
+
+        $this->assertEquals(
+            self::sortArray([
+                $contact2->getId(),
+                $contact3->getId(),
+            ]),
+            self::sortArray($opportunity->getLinkMultipleIdList('contacts'))
+        );
+
+        $column3 = $entityManager
+            ->getRDBRepository('Opportunity')
+            ->getRelation($opportunity, 'contacts')
+            ->getColumn($contact3, 'role');
+
+        $this->assertEquals('Evaluator', $column3);
+
+        $opportunity = $entityManager->getEntity('Opportunity', $opportunity->getId());
+
+        $opportunity->set([
+            'contactsColumns' => (object) [
+                $contact3->getId() => (object) [
+                    'role' => 'Decision Maker',
+                ],
+            ],
+        ]);
+
+        $entityManager->saveEntity($opportunity);
+
+        $column3 = $entityManager
+            ->getRDBRepository('Opportunity')
+            ->getRelation($opportunity, 'contacts')
+            ->getColumn($contact3, 'role');
+
+        $this->assertEquals('Decision Maker', $column3);
+    }
+
+    public function testHasOne(): void
+    {
+        /* @var $entityManager EntityManager */
+        $entityManager = $this->getContainer()->get('entityManager');
+
+        $lead1 = $entityManager->createEntity('Lead', []);
+        $lead2 = $entityManager->createEntity('Lead', []);
+
+        $account = $entityManager->createEntity('Account', []);
+
+        $lead1->set('createdAccountId', $account->getId());
+
+        $entityManager->saveEntity($lead1);
+
+        $lead2->set('createdAccountId', $account->getId());
+
+        $entityManager->saveEntity($lead2);
+
+        $lead1 = $entityManager->getEntity('Lead', $lead1->getId());
+
+        $this->assertNull($lead1->get('createdAccountId'));
+
+        $lead2 = $entityManager->getEntity('Lead', $lead2->getId());
+
+        $this->assertEquals($account->getId(), $lead2->get('createdAccountId'));
+    }
+
+    public function testBelongsToHasOne(): void
+    {
+        /* @var $entityManager EntityManager */
+        $entityManager = $this->getContainer()->get('entityManager');
+
+        $lead1 = $entityManager->createEntity('Lead', []);
+        $lead2 = $entityManager->createEntity('Lead', []);
+
+        $account = $entityManager->createEntity('Account', [
+            'originalLeadId' => $lead1->getId(),
+        ]);
+
+        $entityManager->saveEntity($account);
+
+        $account = $entityManager->getEntity('Account', $account->getId());
+
+        $account->set([
+            'originalLeadId' => $lead2->getId(),
+        ]);
+
+        $entityManager->saveEntity($account);
+
+        $lead2 = $entityManager->getEntity('Lead', $lead2->getId());
+
+        $this->assertEquals($account->getId(), $lead2->get('createdAccountId'));
+
+        $lead1 = $entityManager->getEntity('Lead', $lead1->getId());
+
+        $this->assertEquals(null, $lead1->get('createdAccountId'));
+    }
+
+    private static function sortArray(array $array): array
+    {
+        sort($array);
+
+        return $array;
+    }
+}