feat: Add distinct method to FakeQuerySet (#188)

Fixes #29

CHANGELOG.txt

@@ -5,6 +5,7 @@ Changelog
 ~~~~~~~~~~~~~~~~
 * Support filtering with Q objects (Shohan Dutta Roy)
 * Support random ordering with `.order_by("?")` (Shohan Dutta Roy)
+* Support `distinct()` on querysets (Shohan Dutta Roy)
 * Fix: Correctly handle filtering on fields on related models when those fields have names that match a lookup type (Andy Babic)
 * Fix: Correctly handle null foreign keys when traversing related fields (Andy Babic)
 

modelcluster/queryset.py

@@ -672,6 +672,18 @@ def order_by(self, *fields):
         sort_by_fields(clone.results, fields)
         return clone
 
+    def distinct(self, *fields):
+        unique_results = []
+        if not fields:
+            fields = [field.name for field in self.model._meta.fields if not field.primary_key]
+        seen_keys = set()
+        for result in self.results:
+            key = tuple(str(extract_field_value(result, field)) for field in fields)
+            if key not in seen_keys:
+                seen_keys.add(key)
+                unique_results.append(result)
+        return self.get_clone(results=unique_results)
+
     # a standard QuerySet will store the results in _result_cache on running the query;
     # this is effectively the same as self.results on a FakeQuerySet, and so we'll make
     # _result_cache an alias of self.results for the benefit of Django internals that

tests/tests/test_cluster.py

@@ -864,6 +864,28 @@ def test_meta_ordering(self):
         albums = [album.name for album in beatles.albums.all()]
         self.assertEqual(['With The Beatles', 'Please Please Me', 'Abbey Road'], albums)
 
+    def test_distinct_with_no_fields(self):
+        beatles = Band(name='The Beatles', albums=[
+            Album(name='Please Please Me', sort_order=1),
+            Album(name='With The Beatles', sort_order=2),
+            Album(name='Abbey Road', sort_order=2),
+        ])
+
+        albums = [album.name for album in beatles.albums.order_by('sort_order').distinct()]
+        self.assertEqual(['Please Please Me', 'With The Beatles', 'Abbey Road'], albums)
+
+    def test_distinct_with_fields(self):
+        beatles = Band(name='The Beatles', albums=[
+            Album(name='Please Please Me', sort_order=1),
+            Album(name='With The Beatles', sort_order=2),
+            Album(name='Abbey Road', sort_order=2),
+        ])
+        albums = [album.name for album in beatles.albums.order_by('sort_order').distinct('sort_order')]
+        self.assertEqual(['Please Please Me', 'With The Beatles'], albums)
+
+        albums = [album.name for album in beatles.albums.order_by('sort_order').distinct('name')]
+        self.assertEqual(['Please Please Me', 'With The Beatles', 'Abbey Road'], albums)
+
     def test_parental_key_checks_clusterable_model(self):
         from django.core import checks
         from django.db import models