fix the order when getting next or prev post and at the post view

fet2020/posts/managers.py

@@ -37,7 +37,7 @@ class PostManager(PublishedManager, models.Manager):
                 When(post_type="F", then="event_start__date"),
             )
         )
-        return qs.order_by("-date")
+        return qs.order_by("-date", "-id")
 
     def date_sorted_list(self, public=True):
         return self.published(public)
@@ -76,7 +76,7 @@ class ArticleManager(PublishedManager, models.Manager):
                 When(post_type="E", then="event_start__date"),
             )
         )
-        return qs.order_by("-date")
+        return qs.order_by("-date", "-id")
 
     def date_sorted_list(self, public=True):
         return self.published(public)

fet2020/posts/views.py

@@ -4,6 +4,7 @@ from datetime import timedelta
 from django.conf import settings
 from django.contrib.auth.mixins import LoginRequiredMixin
 from django.http import Http404, HttpResponse
+from django.db.models import Q
 from django.shortcuts import render
 from django.template.loader import render_to_string
 from django.views.generic.detail import DetailView
@@ -147,9 +148,15 @@ class PostDetailView(DetailView):
         posts = Post.objects.date_sorted_list(self.public_only).filter(
             post_type=self.object.post_type
         )
-        qs = posts.filter(date__lt=self.object.date)
+        qs = posts.filter(
+            # Get posts which are in the future.
+            Q(date__lt=self.object.date)
+            # Get posts which have the same date but id is lower.
+            | (Q(date__lte=self.object.date) & Q(id__lt=self.object.id))
+        )
         if not qs:
-            qs = posts[:1]
+            # If there are any prev posts, then take the latest one.
+            qs = posts
 
         return qs.first().slug
 
@@ -162,9 +169,15 @@ class PostDetailView(DetailView):
             .filter(post_type=self.object.post_type)
             .reverse()
         )
-        qs = posts.filter(date__gt=self.object.date)
+        qs = posts.filter(
+            # Get posts which are in the past.
+            Q(date__gt=self.object.date)
+            # Get posts which have the same date but id is greater.
+            | (Q(date__gte=self.object.date) & Q(id__gt=self.object.id))
+        )
         if not qs:
-            qs = posts[:1]
+            # If there are any next posts, then take the first one.
+            qs = posts
 
         return qs.first().slug