diff --git a/publications/admin.py b/publications/admin.py
index 8fb973b..2f7ad35 100644
--- a/publications/admin.py
+++ b/publications/admin.py
@@ -1,9 +1,9 @@
 from django.contrib import admin
-from .models import Publication, Rating
+from .models import Publication, Rating, Category
 
 # Register your models here.
 class PublicationAdmin(admin.ModelAdmin):
-    list_display = ('pk', 'content_type', 'is_pinned', 'user', 'time_created', 'time_updated')
+    list_display = ('pk', 'content_type', 'category', 'is_pinned', 'user', 'time_created', 'time_updated')
     list_display_links = ('pk', 'content_type')
     list_filter = ('content_type', 'is_pinned')
     readonly_fields = ('time_created', 'time_updated')
@@ -16,4 +16,5 @@ class RatingAdmin(admin.ModelAdmin):
     search_fields = ('user__username', )
 
 admin.site.register(Publication, PublicationAdmin)
-admin.site.register(Rating, RatingAdmin)
\ No newline at end of file
+admin.site.register(Rating, RatingAdmin)
+admin.site.register(Category)
\ No newline at end of file
diff --git a/publications/managers.py b/publications/managers.py
index de85fa0..3f1061b 100644
--- a/publications/managers.py
+++ b/publications/managers.py
@@ -1,5 +1,6 @@
 from typing import TypeVar
 from django.db.models import Avg
+from django.db.models.functions import Coalesce
 from django.db import models
 
 T = TypeVar('T')
@@ -7,7 +8,7 @@ T = TypeVar('T')
 class PublicationQuerySet(models.QuerySet[T]):
     def with_score(self):
         qs = self
-        qs = qs.annotate(average_score=Avg("ratings__score"))
+        qs = qs.annotate(average_score=Coalesce(Avg("ratings__score"), 0.0))
         return qs
     
     def only_publish(self):
diff --git a/publications/models.py b/publications/models.py
index 28ff923..1ebf30c 100644
--- a/publications/models.py
+++ b/publications/models.py
@@ -47,10 +47,6 @@ class Publication(models.Model):
 
     def __str__(self):
         return f'Content #{self.pk}'
-    
-    @property
-    def average_score(self) -> int:
-        return getattr(self, "average_score", None)
 
     def clean(self):
         errors = []
diff --git a/publications/serializers.py b/publications/serializers.py
index 3f28fbb..050d044 100644
--- a/publications/serializers.py
+++ b/publications/serializers.py
@@ -12,7 +12,31 @@ class CategorySerializer(serializers.ModelSerializer):
 class PublicationSerializer(serializers.ModelSerializer):
     category_detail = CategorySerializer(source="category", read_only=True)
     user_detail = PublicUserSerializer(source="user", read_only=True)
-    average_score = serializers.IntegerField(read_only=True)
+    average_score = serializers.SerializerMethodField(read_only=True)
+
+    def get_average_score(self, obj):
+        return getattr(obj, 'average_score', 0)
+    
+    def validate(self, attrs):
+        content_type = attrs.get('content_type')
+        image = attrs.get('image')
+        video = attrs.get('video')
+
+        errors = {}
+
+        if content_type == 'image' and not image:
+            errors['image'] = 'Required image file'
+
+        if content_type == 'video' and not video:
+            errors['video'] = 'Required video file'
+
+        if image and video:
+            errors['non_field_errors'] = 'You must upload either a video or an image, not both'
+
+        if errors:
+            raise serializers.ValidationError(errors)
+
+        return attrs
 
     class Meta:
         model = Publication
diff --git a/publications/views.py b/publications/views.py
index 99d1ed4..22d60de 100644
--- a/publications/views.py
+++ b/publications/views.py
@@ -39,6 +39,9 @@ class PublicationsAPIView(ListCreateAPIView):
             return [IsAuthenticated()]
          
         return super().get_permissions()
+    
+    def perform_create(self, serializer: PublicationSerializer):
+        serializer.save(user=self.request.user)
 
 @extend_schema(
     tags=['Publications'],
@@ -66,6 +69,9 @@ class AdminPublicationsAPIView(PublicationsAPIView):
 
     def get_permissions(self):
         return [IsProfessorOnly()]
+    
+    def perform_create(self, serializer: AdminPublicationSerializer):
+        serializer.save(user=self.request.user)
 
 @extend_schema(
     tags=['Publications'],
@@ -92,10 +98,11 @@ class CategoryListAPIView(ListCreateAPIView):
     filter_backends = [filters.SearchFilter, filters.OrderingFilter]
     ordering = ['name']
     search_fields = ['name']
+    pagination_class = None
 
     def get_permissions(self):
         if self.request.method == 'POST':
-            return [IsAdminUser]
+            return [IsAdminUser()]
         return super().get_permissions()
 
 @extend_schema(
diff --git a/users/views.py b/users/views.py
index 3b1b9fa..8658e64 100644
--- a/users/views.py
+++ b/users/views.py
@@ -5,7 +5,7 @@ from rest_framework.request import Request
 from rest_framework.response import Response
 from rest_framework import status
 from rest_framework.views import APIView
-from rest_framework.generics import RetrieveUpdateDestroyAPIView, ListAPIView, RetrieveAPIView
+from rest_framework.generics import RetrieveUpdateDestroyAPIView, ListAPIView, RetrieveAPIView, ListCreateAPIView
 from rest_framework.permissions import IsAuthenticated, IsAdminUser
 from rest_framework.authtoken.models import Token
 
@@ -87,9 +87,17 @@ class UserAPIView(RetrieveUpdateDestroyAPIView):
     serializer_class = UserForAdminSerializer
     permission_classes = [IsAdminUser]
 
-@extend_schema(tags=['Users'],
-                summary='List of all available school ids (only admin)')
-class SchoolListAPIView(ListAPIView):
+@extend_schema(
+    tags=['Users'],
+    methods=['GET'],
+    summary='List school ids',
+)
+@extend_schema(
+    tags=['Users'],
+    methods=['POST'],
+    summary='Create new school id (only admin)',
+)
+class SchoolListAPIView(ListCreateAPIView):
     queryset = SchoolID.objects.all()
     serializer_class = SchoolIDSerializer
     permission_classes = [IsAdminUser]