diff --git a/cvat/apps/engine/models.py b/cvat/apps/engine/models.py
index c9d480cface..375e608d3b8 100644
--- a/cvat/apps/engine/models.py
+++ b/cvat/apps/engine/models.py
@@ -1315,8 +1315,10 @@ class AnnotationGuide(TimestampedModel):
     is_public = models.BooleanField(default=False)
 
     @property
-    def target(self):
-        return self.project or self.task
+    def target(self) -> Task | Project:
+        target = self.project or self.task
+        assert target # one of the fields must be set
+        return target
 
     @property
     def organization_id(self):
diff --git a/cvat/apps/engine/permissions.py b/cvat/apps/engine/permissions.py
index 8c7c809e2ab..d26a700f0da 100644
--- a/cvat/apps/engine/permissions.py
+++ b/cvat/apps/engine/permissions.py
@@ -22,7 +22,7 @@
 )
 from cvat.apps.organizations.models import Organization
 
-from .models import AnnotationGuide, CloudStorage, Issue, Job, Label, Project, Task
+from .models import AnnotationGuide, CloudStorage, Comment, Issue, Job, Label, Project, Task, User
 
 
 def _get_key(d: dict[str, Any], key_path: Union[str, Sequence[str]]) -> Optional[Any]:
@@ -75,6 +75,8 @@ def get_resource(self):
         return None
 
 class UserPermission(OpenPolicyAgentPermission):
+    obj: Optional[User]
+
     class Scopes(StrEnum):
         LIST = 'list'
         VIEW = 'view'
@@ -134,6 +136,8 @@ def get_resource(self):
         return data
 
 class CloudStoragePermission(OpenPolicyAgentPermission):
+    obj: Optional[CloudStorage]
+
     class Scopes(StrEnum):
         LIST = 'list'
         LIST_CONTENT = 'list:content'
@@ -196,15 +200,17 @@ def get_resource(self):
         elif self.obj:
             data = {
                 'id': self.obj.id,
-                'owner': { 'id': getattr(self.obj.owner, 'id', None) },
+                'owner': { 'id': self.obj.owner_id },
                 'organization': {
-                    'id': self.obj.organization.id
-                } if self.obj.organization else None
+                    'id': self.obj.organization_id
+                } if self.obj.organization_id else None
             }
 
         return data
 
 class ProjectPermission(OpenPolicyAgentPermission):
+    obj: Optional[Project]
+
     class Scopes(StrEnum):
         LIST = 'list'
         CREATE = 'create'
@@ -345,11 +351,9 @@ def get_resource(self):
         if self.obj:
             data = {
                 "id": self.obj.id,
-                "owner": { "id": getattr(self.obj.owner, 'id', None) },
-                "assignee": { "id": getattr(self.obj.assignee, 'id', None) },
-                'organization': {
-                    "id": getattr(self.obj.organization, 'id', None)
-                }
+                "owner": { "id": self.obj.owner_id },
+                "assignee": { "id": self.obj.assignee_id },
+                'organization': { "id": self.obj.organization_id },
             }
         elif self.scope in [__class__.Scopes.CREATE, __class__.Scopes.IMPORT_BACKUP]:
             data = {
@@ -357,7 +361,7 @@ def get_resource(self):
                 "owner": { "id": self.user_id },
                 "assignee": {
                     "id": self.assignee_id,
-                } if getattr(self, 'assignee_id', None) else None,
+                } if self.assignee_id else None,
                 'organization': {
                     "id": self.org_id,
                 } if self.org_id else None,
@@ -366,6 +370,8 @@ def get_resource(self):
         return data
 
 class TaskPermission(OpenPolicyAgentPermission):
+    obj: Optional[Task]
+
     class Scopes(StrEnum):
         LIST = 'list'
         CREATE = 'create'
@@ -558,17 +564,13 @@ def get_resource(self):
         if self.obj:
             data = {
                 "id": self.obj.id,
-                "owner": { "id": getattr(self.obj.owner, 'id', None) },
-                "assignee": { "id": getattr(self.obj.assignee, 'id', None) },
-                'organization': {
-                    "id": getattr(self.obj.organization, 'id', None)
-                },
+                "owner": { "id": self.obj.owner_id },
+                "assignee": { "id": self.obj.assignee_id },
+                'organization': { "id": self.obj.organization_id },
                 "project": {
-                    "owner": { "id": getattr(self.obj.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(self.obj.project.assignee, 'id', None) },
-                    'organization': {
-                        "id": getattr(self.obj.project.organization, 'id', None)
-                    },
+                    "owner": { "id": self.obj.project.owner_id },
+                    "assignee": { "id": self.obj.project.assignee_id },
+                    'organization': { "id": self.obj.project.organization_id },
                 } if self.obj.project else None
             }
         elif self.scope in [
@@ -593,11 +595,11 @@ def get_resource(self):
                     "id": self.org_id
                 },
                 "project": {
-                    "owner": { "id": getattr(project.owner, 'id', None) },
-                    "assignee": { "id": getattr(project.assignee, 'id', None) },
+                    "owner": { "id": project.owner_id },
+                    "assignee": { "id": project.assignee_id },
                     'organization': {
-                        "id": getattr(project.organization, 'id', None),
-                    } if project.organization is not None else None,
+                        "id": project.organization_id,
+                    } if project.organization_id else None,
                 } if project is not None else None,
             }
 
@@ -605,6 +607,7 @@ def get_resource(self):
 
 class JobPermission(OpenPolicyAgentPermission):
     task_id: Optional[int]
+    obj: Optional[Job]
 
     class Scopes(StrEnum):
         CREATE = 'create'
@@ -751,23 +754,21 @@ def get_resource(self):
         data = None
         if self.obj:
             if self.obj.segment.task.project:
-                organization = self.obj.segment.task.project.organization
+                organization_id = self.obj.segment.task.project.organization_id
             else:
-                organization = self.obj.segment.task.organization
+                organization_id = self.obj.segment.task.organization_id
 
             data = {
                 "id": self.obj.id,
-                "assignee": { "id": getattr(self.obj.assignee, 'id', None) },
-                'organization': {
-                    "id": getattr(organization, 'id', None)
-                },
+                "assignee": { "id": self.obj.assignee_id },
+                'organization': { "id": organization_id },
                 "task": {
-                    "owner": { "id": getattr(self.obj.segment.task.owner, 'id', None) },
-                    "assignee": { "id": getattr(self.obj.segment.task.assignee, 'id', None) }
+                    "owner": { "id": self.obj.segment.task.owner_id },
+                    "assignee": { "id": self.obj.segment.task.assignee_id }
                 },
                 "project": {
-                    "owner": { "id": getattr(self.obj.segment.task.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(self.obj.segment.task.project.assignee, 'id', None) }
+                    "owner": { "id": self.obj.segment.task.project.owner_id },
+                    "assignee": { "id": self.obj.segment.task.project.assignee_id }
                 } if self.obj.segment.task.project else None
             }
         elif self.scope == __class__.Scopes.CREATE:
@@ -776,27 +777,27 @@ def get_resource(self):
             task = Task.objects.get(id=self.task_id)
 
             if task.project:
-                organization = task.project.organization
+                organization_id = task.project.organization_id
             else:
-                organization = task.organization
+                organization_id = task.organization_id
 
             data = {
-                'organization': {
-                    "id": getattr(organization, 'id', None)
-                },
+                'organization': { "id": organization_id },
                 "task": {
-                    "owner": { "id": getattr(task.owner, 'id', None) },
-                    "assignee": { "id": getattr(task.assignee, 'id', None) }
+                    "owner": { "id": task.owner_id },
+                    "assignee": { "id": task.assignee_id }
                 },
                 "project": {
-                    "owner": { "id": getattr(task.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(task.project.assignee, 'id', None) }
+                    "owner": { "id": task.project.owner_id },
+                    "assignee": { "id": task.project.assignee_id }
                 } if task.project else None
             }
 
         return data
 
 class CommentPermission(OpenPolicyAgentPermission):
+    obj: Optional[Comment]
+
     class Scopes(StrEnum):
         LIST = 'list'
         CREATE  = 'create'
@@ -835,29 +836,27 @@ def get_resource(self):
         data = None
         def get_common_data(db_issue):
             if db_issue.job.segment.task.project:
-                organization = db_issue.job.segment.task.project.organization
+                organization_id = db_issue.job.segment.task.project.organization_id
             else:
-                organization = db_issue.job.segment.task.organization
+                organization_id = db_issue.job.segment.task.organization_id
 
             data = {
                 "project": {
-                    "owner": { "id": getattr(db_issue.job.segment.task.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(db_issue.job.segment.task.project.assignee, 'id', None) }
+                    "owner": { "id": db_issue.job.segment.task.project.owner_id },
+                    "assignee": { "id": db_issue.job.segment.task.project.assignee_id }
                 } if db_issue.job.segment.task.project else None,
                 "task": {
-                    "owner": { "id": getattr(db_issue.job.segment.task.owner, 'id', None) },
-                    "assignee": { "id": getattr(db_issue.job.segment.task.assignee, 'id', None) }
+                    "owner": { "id": db_issue.job.segment.task.owner_id},
+                    "assignee": { "id": db_issue.job.segment.task.assignee_id }
                 },
                 "job": {
-                    "assignee": { "id": getattr(db_issue.job.assignee, 'id', None) }
+                    "assignee": { "id": db_issue.job.assignee_id }
                 },
                 "issue": {
-                    "owner": { "id": getattr(db_issue.owner, 'id', None) },
-                    "assignee": { "id": getattr(db_issue.assignee, 'id', None) }
+                    "owner": { "id": db_issue.owner_id},
+                    "assignee": { "id": db_issue.assignee_id }
                 },
-                'organization': {
-                    "id": getattr(organization, 'id', None)
-                }
+                'organization': { "id": organization_id }
             }
 
             return data
@@ -882,6 +881,8 @@ def get_common_data(db_issue):
         return data
 
 class IssuePermission(OpenPolicyAgentPermission):
+    obj: Optional[Issue]
+
     class Scopes(StrEnum):
         LIST = 'list'
         CREATE  = 'create'
@@ -927,24 +928,24 @@ def get_resource(self):
         data = None
         def get_common_data(db_job):
             if db_job.segment.task.project:
-                organization = db_job.segment.task.project.organization
+                organization_id = db_job.segment.task.project.organization_id
             else:
-                organization = db_job.segment.task.organization
+                organization_id = db_job.segment.task.organization_id
 
             data = {
                 "project": {
-                    "owner": { "id": getattr(db_job.segment.task.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(db_job.segment.task.project.assignee, 'id', None) }
+                    "owner": { "id": db_job.segment.task.project.owner_id },
+                    "assignee": { "id": db_job.segment.task.project.assignee_id }
                 } if db_job.segment.task.project else None,
                 "task": {
-                    "owner": { "id": getattr(db_job.segment.task.owner, 'id', None) },
-                    "assignee": { "id": getattr(db_job.segment.task.assignee, 'id', None) }
+                    "owner": { "id": db_job.segment.task.owner_id },
+                    "assignee": { "id": db_job.segment.task.assignee_id }
                 },
                 "job": {
-                    "assignee": { "id": getattr(db_job.assignee, 'id', None) }
+                    "assignee": { "id": db_job.assignee_id }
                 },
                 'organization': {
-                    "id": getattr(organization, 'id', None)
+                    "id": organization_id
                 }
             }
 
@@ -955,8 +956,8 @@ def get_common_data(db_job):
             data = get_common_data(db_job)
             data.update({
                 "id": self.obj.id,
-                "owner": { "id": getattr(self.obj.owner, 'id', None) },
-                "assignee": { "id": getattr(self.obj.assignee, 'id', None) }
+                "owner": { "id": self.obj.owner_id },
+                "assignee": { "id": self.obj.assignee_id }
             })
         elif self.scope.startswith(__class__.Scopes.CREATE):
             job_id = self.job_id
@@ -1052,28 +1053,28 @@ def get_resource(self):
 
         if self.obj:
             if self.obj.project:
-                organization = self.obj.project.organization
+                organization_id = self.obj.project.organization_id
             else:
-                organization = self.obj.task.organization
+                organization_id = self.obj.task.organization_id
 
             data = {
                 "id": self.obj.id,
-                'organization': {
-                    "id": getattr(organization, 'id', None)
-                },
+                'organization': { "id": organization_id },
                 "task": {
-                    "owner": { "id": getattr(self.obj.task.owner, 'id', None) },
-                    "assignee": { "id": getattr(self.obj.task.assignee, 'id', None) }
+                    "owner": { "id": self.obj.task.owner_id },
+                    "assignee": { "id": self.obj.task.assignee_id }
                 } if self.obj.task else None,
                 "project": {
-                    "owner": { "id": getattr(self.obj.project.owner, 'id', None) },
-                    "assignee": { "id": getattr(self.obj.project.assignee, 'id', None) }
+                    "owner": { "id": self.obj.project.owner_id },
+                    "assignee": { "id": self.obj.project.assignee_id }
                 } if self.obj.project else None,
             }
 
         return data
 
 class AnnotationGuidePermission(OpenPolicyAgentPermission):
+    obj: Optional[AnnotationGuide]
+
     class Scopes(StrEnum):
         VIEW = 'view'
         UPDATE = 'update'
@@ -1112,16 +1113,15 @@ def get_scopes(request, view, obj):
     def get_resource(self):
         data = {}
         if self.obj:
-            db_target = getattr(self.obj, 'target', {})
-            db_organization = getattr(db_target, 'organization', {})
+            db_target = self.obj.target
             data.update({
                 'id': self.obj.id,
                 'target': {
-                    'owner': { 'id': getattr(getattr(db_target, 'owner', {}), 'id', None) },
-                    'assignee': { 'id': getattr(getattr(db_target, 'assignee', {}), 'id', None) },
+                    'owner': { 'id': db_target.owner_id },
+                    'assignee': { 'id': db_target.assignee_id },
                     'is_job_staff': db_target.is_job_staff(self.user_id),
                 },
-                'organization': { 'id': getattr(db_organization, 'id', None) }
+                'organization': { 'id': self.obj.organization_id }
             })
         elif self.scope == __class__.Scopes.CREATE:
             db_target = None
@@ -1135,13 +1135,14 @@ def get_resource(self):
                     db_target = Task.objects.get(id=self.task_id)
                 except Task.DoesNotExist as ex:
                     raise ValidationError(str(ex))
-            db_organization = getattr(db_target, 'organization', {})
+
+            organization_id = getattr(db_target, 'organization_id', None)
             data.update({
                 'target': {
-                    'owner': { 'id': db_target.owner.id },
-                    'assignee': { 'id': getattr(db_target.assignee, 'id', None) }
+                    'owner': { 'id': getattr(db_target, "owner_id", None) },
+                    'assignee': { 'id': getattr(db_target, "assignee_id", None) },
                 },
-                'organization': { 'id': getattr(db_organization, 'id', None) }
+                'organization': { 'id': organization_id }
             })
         return data
 
diff --git a/cvat/apps/engine/serializers.py b/cvat/apps/engine/serializers.py
index 88429019049..af8bfc759f2 100644
--- a/cvat/apps/engine/serializers.py
+++ b/cvat/apps/engine/serializers.py
@@ -2465,10 +2465,14 @@ class Meta:
 
     def to_representation(self, instance):
         response = super().to_representation(instance)
-        task_subsets = {task.subset for task in instance.tasks.all()}
-        task_subsets.discard('')
+
+        task_subsets = {task.subset for task in instance.tasks.all() if task.subset}
+        task_dimension = next(
+            (task.dimension for task in instance.tasks.all() if task.dimension),
+            None
+        )
         response['task_subsets'] = list(task_subsets)
-        response['dimension'] = getattr(instance.tasks.first(), 'dimension', None)
+        response['dimension'] = task_dimension
         return response
 
 class ProjectWriteSerializer(serializers.ModelSerializer):
diff --git a/cvat/apps/organizations/permissions.py b/cvat/apps/organizations/permissions.py
index f56741e83cc..a3880110673 100644
--- a/cvat/apps/organizations/permissions.py
+++ b/cvat/apps/organizations/permissions.py
@@ -50,7 +50,7 @@ def get_resource(self):
             membership = Membership.objects.filter(organization=self.obj, user=self.user_id).first()
             return {
                 "id": self.obj.id,
-                "owner": {"id": getattr(self.obj.owner, "id", None)},
+                "owner": {"id": self.obj.owner_id},
                 "user": {"role": membership.role if membership else None},
             }
         elif self.scope.startswith(__class__.Scopes.CREATE.value):
@@ -108,10 +108,10 @@ def get_resource(self):
         data = None
         if self.obj:
             data = {
-                "owner": {"id": getattr(self.obj.owner, "id", None)},
-                "invitee": {"id": getattr(self.obj.membership.user, "id", None)},
+                "owner": {"id": self.obj.owner_id},
+                "invitee": {"id": self.obj.membership.user_id},
                 "role": self.obj.membership.role,
-                "organization": {"id": self.obj.membership.organization.id},
+                "organization": {"id": self.obj.membership.organization_id},
             }
         elif self.scope.startswith(__class__.Scopes.CREATE.value):
             data = {
@@ -181,8 +181,8 @@ def get_resource(self):
             return {
                 "role": self.obj.role,
                 "is_active": self.obj.is_active,
-                "user": {"id": self.obj.user.id},
-                "organization": {"id": self.obj.organization.id},
+                "user": {"id": self.obj.user_id},
+                "organization": {"id": self.obj.organization_id},
             }
         else:
             return None
diff --git a/cvat/apps/quality_control/permissions.py b/cvat/apps/quality_control/permissions.py
index 121c71e3252..10aab67d6a7 100644
--- a/cvat/apps/quality_control/permissions.py
+++ b/cvat/apps/quality_control/permissions.py
@@ -139,25 +139,25 @@ def get_resource(self):
 
             if task and task.project:
                 project = task.project
-                organization = project.organization
+                organization_id = project.organization_id
             else:
-                organization = getattr(task, "organization", None)
+                organization_id = task.organization_id
 
             data = {
                 "id": obj_id,
-                "organization": {"id": getattr(organization, "id", None)},
+                "organization": {"id": organization_id},
                 "task": (
                     {
-                        "owner": {"id": getattr(task.owner, "id", None)},
-                        "assignee": {"id": getattr(task.assignee, "id", None)},
+                        "owner": {"id": task.owner_id},
+                        "assignee": {"id": task.assignee_id},
                     }
                     if task
                     else None
                 ),
                 "project": (
                     {
-                        "owner": {"id": getattr(project.owner, "id", None)},
-                        "assignee": {"id": getattr(project.assignee, "id", None)},
+                        "owner": {"id": project.owner_id},
+                        "assignee": {"id": project.assignee_id},
                     }
                     if project
                     else None
@@ -279,25 +279,25 @@ def get_resource(self):
         if self.obj:
             task = self.obj.task
             if task.project:
-                organization = task.project.organization
+                organization_id = task.project.organization_id
             else:
-                organization = task.organization
+                organization_id = task.organization_id
 
             data = {
                 "id": self.obj.id,
-                "organization": {"id": getattr(organization, "id", None)},
+                "organization": {"id": organization_id},
                 "task": (
                     {
-                        "owner": {"id": getattr(task.owner, "id", None)},
-                        "assignee": {"id": getattr(task.assignee, "id", None)},
+                        "owner": {"id": task.owner_id},
+                        "assignee": {"id": task.assignee_id},
                     }
                     if task
                     else None
                 ),
                 "project": (
                     {
-                        "owner": {"id": getattr(task.project.owner, "id", None)},
-                        "assignee": {"id": getattr(task.project.assignee, "id", None)},
+                        "owner": {"id": task.project.owner_id},
+                        "assignee": {"id": task.project.assignee_id},
                     }
                     if task.project
                     else None
diff --git a/cvat/apps/webhooks/permissions.py b/cvat/apps/webhooks/permissions.py
index ecfe82e4fc4..1e6295fabf3 100644
--- a/cvat/apps/webhooks/permissions.py
+++ b/cvat/apps/webhooks/permissions.py
@@ -3,6 +3,8 @@
 #
 # SPDX-License-Identifier: MIT
 
+from typing import Optional
+
 from django.conf import settings
 from rest_framework.exceptions import ValidationError
 
@@ -10,10 +12,12 @@
 from cvat.apps.engine.permissions import ProjectPermission, UserPermission
 from cvat.apps.iam.permissions import OpenPolicyAgentPermission, StrEnum
 
-from .models import WebhookTypeChoice
+from .models import Webhook, WebhookTypeChoice
 
 
 class WebhookPermission(OpenPolicyAgentPermission):
+    obj: Optional[Webhook]
+
     class Scopes(StrEnum):
         CREATE = "create"
         CREATE_IN_PROJECT = "create@project"
@@ -81,12 +85,12 @@ def get_resource(self):
         if self.obj:
             data = {
                 "id": self.obj.id,
-                "owner": {"id": getattr(self.obj.owner, "id", None)},
-                "organization": {"id": getattr(self.obj.organization, "id", None)},
+                "owner": {"id": self.obj.owner_id},
+                "organization": {"id": self.obj.organization_id},
                 "project": None,
             }
-            if self.obj.type == "project" and getattr(self.obj, "project", None):
-                data["project"] = {"owner": {"id": getattr(self.obj.project.owner, "id", None)}}
+            if self.obj.type == "project" and self.obj.project_id:
+                data["project"] = {"owner": {"id": self.obj.project.owner_id}}
         elif self.scope in [
             __class__.Scopes.CREATE,
             __class__.Scopes.CREATE_IN_PROJECT,
@@ -108,9 +112,9 @@ def get_resource(self):
                     {
                         "owner": (
                             {
-                                "id": project.owner.id,
+                                "id": project.owner_id,
                             }
-                            if project.owner
+                            if project.owner_id
                             else None
                         ),
                     }