fix: allow subset instead of all api/download_strucures call

Also fixes 1286 (Cannot filter a query once a slice has been taken)

viewer/download_structures.py

@@ -749,7 +749,13 @@ def create_or_return_download_link(request, target, site_observations):
 
     # Log the provided SiteObservations
     num_given_site_obs = site_observations.count()
-    site_ob_repr = "".join("%r " % site_ob for site_ob in site_observations)
+    site_ob_repr = "".join(
+        # & syntax copies the queryset without evaluating it. this way
+        # I have an unsliced queryset for later for protein_garbage
+        # filter method (this is what gave sliced queryset error)
+        "%r " % site_ob
+        for site_ob in site_observations & site_observations
+    )
     logger.debug(
         'Given %s SiteObservation records: %r', num_given_site_obs, site_ob_repr
     )
@@ -761,8 +767,11 @@ def create_or_return_download_link(request, target, site_observations):
 
     # Remove 'references_' from protein list if present.
     site_observations = _protein_garbage_filter(site_observations)
-    if num_removed := num_given_site_obs - num_given_site_obs:
-        logger.warning('Removed %d "references_" proteins from download', num_removed)
+    if num_given_site_obs > site_observations.count():
+        logger.warning(
+            'Removed %d "references_" proteins from download',
+            num_given_site_obs - site_observations.count(),
+        )
 
     # Save the list of protein codes - this is the ispybsafe set for this user.
     proteins_list = list(site_observations.values_list('code', flat=True))

viewer/views.py

@@ -1482,7 +1482,11 @@ def create(self, request):
                     code__contains=code_first_part
                 )
                 if prot.exists():
-                    site_obvs = prot[0:1]
+                    # even more than just django object, I need an
+                    # unevaluated queryset down the line
+                    site_obvs = models.SiteObservation.objects.filter(
+                        pk=prot.first().pk,
+                    )
                 else:
                     logger.warning(
                         'Could not find SiteObservation record for "%s"',