diff --git a/src/Entity/Attachments/AttachmentType.php b/src/Entity/Attachments/AttachmentType.php
index 22333c16..b5d1ff8c 100644
--- a/src/Entity/Attachments/AttachmentType.php
+++ b/src/Entity/Attachments/AttachmentType.php
@@ -47,6 +47,8 @@ use Doctrine\Common\Collections\ArrayCollection;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -93,7 +95,7 @@ class AttachmentType extends AbstractStructuralDBElement
     #[ORM\ManyToOne(targetEntity: AttachmentType::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['attachment_type:read', 'attachment_type:write'])]
-    #[ApiProperty(readableLink: true, writableLink: false)]
+    #[ApiProperty(readableLink: true, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     /**
diff --git a/src/Entity/Parts/Category.php b/src/Entity/Parts/Category.php
index 7fca81bc..a9efd2fa 100644
--- a/src/Entity/Parts/Category.php
+++ b/src/Entity/Parts/Category.php
@@ -50,6 +50,8 @@ use App\Entity\Parameters\CategoryParameter;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -98,7 +100,7 @@ class Category extends AbstractPartsContainingDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['category:read', 'category:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     #[Groups(['category:read', 'category:write'])]
diff --git a/src/Entity/Parts/Footprint.php b/src/Entity/Parts/Footprint.php
index 6b043562..251232c1 100644
--- a/src/Entity/Parts/Footprint.php
+++ b/src/Entity/Parts/Footprint.php
@@ -49,6 +49,8 @@ use App\Entity\Parameters\FootprintParameter;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -93,7 +95,7 @@ class Footprint extends AbstractPartsContainingDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['footprint:read', 'footprint:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     #[ORM\OneToMany(mappedBy: 'parent', targetEntity: self::class)]
diff --git a/src/Entity/Parts/Manufacturer.php b/src/Entity/Parts/Manufacturer.php
index 0edf8232..f7bee4b8 100644
--- a/src/Entity/Parts/Manufacturer.php
+++ b/src/Entity/Parts/Manufacturer.php
@@ -48,6 +48,8 @@ use App\Entity\Parameters\ManufacturerParameter;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -92,7 +94,7 @@ class Manufacturer extends AbstractCompany
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['manufacturer:read', 'manufacturer:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     #[ORM\OneToMany(mappedBy: 'parent', targetEntity: self::class)]
diff --git a/src/Entity/Parts/MeasurementUnit.php b/src/Entity/Parts/MeasurementUnit.php
index 6dd0b9f2..dfb7e1d4 100644
--- a/src/Entity/Parts/MeasurementUnit.php
+++ b/src/Entity/Parts/MeasurementUnit.php
@@ -50,6 +50,8 @@ use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 use Symfony\Component\Validator\Constraints\Length;
 
@@ -130,7 +132,7 @@ class MeasurementUnit extends AbstractPartsContainingDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['measurement_unit:read', 'measurement_unit:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     /**
diff --git a/src/Entity/Parts/PartCustomState.php b/src/Entity/Parts/PartCustomState.php
index 136ff984..77530ff6 100644
--- a/src/Entity/Parts/PartCustomState.php
+++ b/src/Entity/Parts/PartCustomState.php
@@ -46,6 +46,8 @@ use Doctrine\Common\Collections\Collection;
 use Doctrine\Common\Collections\Criteria;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -87,7 +89,7 @@ class PartCustomState extends AbstractPartsContainingDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['part_custom_state:read', 'part_custom_state:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     /**
diff --git a/src/Entity/Parts/StorageLocation.php b/src/Entity/Parts/StorageLocation.php
index 6c455ae5..ca76df59 100644
--- a/src/Entity/Parts/StorageLocation.php
+++ b/src/Entity/Parts/StorageLocation.php
@@ -50,6 +50,8 @@ use App\Entity\UserSystem\User;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -97,7 +99,7 @@ class StorageLocation extends AbstractPartsContainingDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['location:read', 'location:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     #[Groups(['location:read', 'location:write'])]
diff --git a/src/Entity/Parts/Supplier.php b/src/Entity/Parts/Supplier.php
index 2c004e9e..a073e9e4 100644
--- a/src/Entity/Parts/Supplier.php
+++ b/src/Entity/Parts/Supplier.php
@@ -53,6 +53,8 @@ use Brick\Math\BigDecimal;
 use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -99,7 +101,7 @@ class Supplier extends AbstractCompany
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['supplier:read', 'supplier:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     /**
diff --git a/src/Entity/PriceInformations/Currency.php b/src/Entity/PriceInformations/Currency.php
index ce20caf8..4bf9df4e 100644
--- a/src/Entity/PriceInformations/Currency.php
+++ b/src/Entity/PriceInformations/Currency.php
@@ -52,6 +52,8 @@ use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 
 /**
@@ -125,7 +127,7 @@ class Currency extends AbstractStructuralDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['currency:read', 'currency:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     /**
diff --git a/src/Entity/ProjectSystem/Project.php b/src/Entity/ProjectSystem/Project.php
index a103d694..53f74af0 100644
--- a/src/Entity/ProjectSystem/Project.php
+++ b/src/Entity/ProjectSystem/Project.php
@@ -49,6 +49,8 @@ use Doctrine\Common\Collections\Collection;
 use Doctrine\ORM\Mapping as ORM;
 use InvalidArgumentException;
 use Symfony\Component\Serializer\Annotation\Groups;
+use Symfony\Component\TypeInfo\Type\NullableType;
+use Symfony\Component\TypeInfo\Type\ObjectType;
 use Symfony\Component\Validator\Constraints as Assert;
 use Symfony\Component\Validator\Context\ExecutionContextInterface;
 
@@ -95,7 +97,7 @@ class Project extends AbstractStructuralDBElement
     #[ORM\ManyToOne(targetEntity: self::class, inversedBy: 'children')]
     #[ORM\JoinColumn(name: 'parent_id')]
     #[Groups(['project:read', 'project:write'])]
-    #[ApiProperty(readableLink: false, writableLink: false)]
+    #[ApiProperty(readableLink: false, writableLink: false, nativeType: new NullableType(new ObjectType(self::class)))]
     protected ?AbstractStructuralDBElement $parent = null;
 
     #[Groups(['project:read', 'project:write'])]