Made some fields in post admin read-only. Show attachment as its url

boards/admin.py

@@ -10,7 +10,8 b' class PostAdmin(admin.ModelAdmin):'
     list_filter = ('pub_time',)
     search_fields = ('id', 'title', 'text', 'poster_ip')
     exclude = ('referenced_posts', 'refmap')
-    readonly_fields = ('poster_ip', 'threads', 'thread', 'images', 'uid')
+    readonly_fields = ('poster_ip', 'threads', 'thread', 'images',
+            'attachments', 'uid', 'url', 'pub_time', 'opening')
 
     def ban_poster(self, request, queryset):
         bans = 0

boards/models/attachment/__init__.py

@@ -38,4 +38,5 b' class Attachment(models.Model):'
 
         return file_viewer(self.file, self.mimetype).get_view()
 
-
+    def __str__(self):
+        return self.file.url