Enhance CaseFilter to show distinct examination values for series, improving clarity in selection options

atlas/filters.py

@@ -2,6 +2,7 @@ import django_filters
 from django import forms
 from crispy_forms.helper import FormHelper
 from crispy_forms.layout import Layout, Div, Field
+from collections import OrderedDict
 
 from .models import (
     Case,
@@ -98,8 +99,12 @@ class CaseFilter(django_filters.FilterSet):
     author = django_filters.ModelMultipleChoiceFilter(
         queryset=get_authors, null_label="No author"
     )
+    # Show a distinct list of `Series.examination` values instead of raw Series
+    # entries so examinations that differ only by plane/description appear once.
     series = django_filters.ModelMultipleChoiceFilter(
-        queryset=get_series, null_label="No series"
+        field_name='series__examination',
+        queryset=lambda request: __import__('generic.models', fromlist=['Examination']).Examination.objects.filter(atlas_series_examination__isnull=False).distinct(),
+        label='Examination',
     )
     differential_case = django_filters.ModelMultipleChoiceFilter(
         label="Differential",