diff --git a/competition/serializers.py b/competition/serializers.py
index 665e15b..9d04d20 100644
--- a/competition/serializers.py
+++ b/competition/serializers.py
@@ -123,13 +123,19 @@ def get_history_events(self, obj):
 
 
 @ts_interface(context='competition')
-class EventRegistrationSerializer(serializers.ModelSerializer):
+class GradeSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = models.Grade
+        exclude = ['is_active']
+
+
+@ts_interface(context='competition')
+class EventRegistrationReadSerializer(serializers.ModelSerializer):
     class Meta:
         model = models.EventRegistration
         fields = ['school', 'grade', 'profile', 'verbose_name', 'id', 'event']
     school = SchoolShortSerializer(many=False)
-    grade = serializers.SlugRelatedField(
-        slug_field='tag', many=False, read_only=True)
+    grade = GradeSerializer(many=False)
     profile = ProfileShortSerializer(many=False)
     verbose_name = serializers.SerializerMethodField('get_verbose_name')
 
@@ -137,6 +143,22 @@ def get_verbose_name(self, obj):
         return str(obj)
 
 
+class EventRegistrationWriteSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = models.EventRegistration
+        fields = ['school', 'grade', 'profile', 'id', 'event']
+
+    id = serializers.ReadOnlyField()
+    school = serializers.PrimaryKeyRelatedField(
+        queryset=models.School.objects.all())
+    grade = serializers.PrimaryKeyRelatedField(
+        queryset=models.Grade.objects.all())
+    profile = serializers.PrimaryKeyRelatedField(
+        queryset=models.Profile.objects.all())
+    event = serializers.PrimaryKeyRelatedField(
+        queryset=models.Event.objects.all())
+
+
 @ts_interface(context='competition')
 class ProblemCorrectionSerializer(serializers.ModelSerializer):
     corrected_by = serializers.SerializerMethodField('get_corrected_by')
@@ -225,7 +247,7 @@ class Meta:
 
 @ts_interface(context='competition')
 class SolutionAdministrationSerializer(serializers.ModelSerializer):
-    semester_registration = EventRegistrationSerializer(read_only=True)
+    semester_registration = EventRegistrationReadSerializer(read_only=True)
 
     class Meta:
         model = models.Solution
@@ -398,10 +420,3 @@ class LateTagSerializer(serializers.ModelSerializer):
     class Meta:
         model = models.LateTag
         exclude = ['comment']
-
-
-@ts_interface(context='competition')
-class GradeSerializer(serializers.ModelSerializer):
-    class Meta:
-        model = models.Grade
-        exclude = ['is_active']
diff --git a/competition/views.py b/competition/views.py
index e5e6fbb..418bea3 100644
--- a/competition/views.py
+++ b/competition/views.py
@@ -28,7 +28,8 @@
                                      ProblemPermission)
 from competition.serializers import (CommentSerializer, CompetitionSerializer,
                                      CompetitionTypeSerializer,
-                                     EventRegistrationSerializer,
+                                     EventRegistrationReadSerializer,
+                                     EventRegistrationWriteSerializer,
                                      EventSerializer, GradeSerializer,
                                      LateTagSerializer, ProblemSerializer,
                                      ProblemWithSolutionsSerializer,
@@ -99,7 +100,7 @@ def generate_result_row(
         # Indikuje či sa zmenilo poradie od minulej priečky, slúži na delené miesta
         'rank_changed': True,
         # primary key riešiteľovej registrácie do semestra
-        'registration': EventRegistrationSerializer(semester_registration).data,
+        'registration': EventRegistrationReadSerializer(semester_registration).data,
         # Súčty bodov po sériách
         'subtotal': subtotal,
         # Celkový súčet za danú entitu
@@ -878,10 +879,14 @@ def active(self, request):
 class EventRegistrationViewSet(viewsets.ModelViewSet):
     """Registrácie na akcie"""
     queryset = EventRegistration.objects.all()
-    serializer_class = EventRegistrationSerializer
     filterset_fields = ['event', 'profile', ]
     permission_classes = (CompetitionRestrictedPermission,)
 
+    def get_serializer_class(self):
+        if self.action in ['list', 'retrieve']:
+            return EventRegistrationReadSerializer
+        return EventRegistrationWriteSerializer
+
 
 class PublicationTypeViewSet(viewsets.ReadOnlyModelViewSet):
     queryset = PublicationType.objects.all()
diff --git a/personal/serializers.py b/personal/serializers.py
index ec72cb0..8783250 100644
--- a/personal/serializers.py
+++ b/personal/serializers.py
@@ -165,7 +165,8 @@ def create(self, validated_data):
 class ProfileShortSerializer(serializers.ModelSerializer):
     class Meta:
         model = Profile
-        fields = ['first_name', 'last_name']
+        fields = ['id', 'first_name', 'last_name']
+        read_only_fields = ['id']
 
 
 @ts_interface(context='personal')