Use django.db.models.Max.aggregate to get nextautoincrement (#1114)

The SQL query was not compatible with postgresql

pod/main/models.py

@@ -9,7 +9,7 @@
 from django.template.defaultfilters import slugify
 from django.dispatch import receiver
 from django.db.models.signals import post_save
-from django.db import connection
+from django.db.models import Max
 import os
 import mimetypes
 from ckeditor.fields import RichTextField
@@ -19,16 +19,11 @@
 
 
 def get_nextautoincrement(model):
-    cursor = connection.cursor()
-    cursor.execute(
-        "SELECT Auto_increment FROM information_schema.tables "
-        + 'WHERE table_name="{0}" AND table_schema=DATABASE();'.format(
-            model._meta.db_table
-        )
-    )
-    row = cursor.fetchone()
-    cursor.close()
-    return row[0]
+    """Get potential next id for the current model when an object will be created"""
+    objects = model.objects.all()
+    if objects:
+        return objects.aggregate(Max("id"))["id__max"] + 1
+    return 1
 
 
 def get_upload_path_files(instance, filename):