Have ThingyList.distinct() handle array fields like MongoDB

mongo_thingy/__init__.py

@@ -26,7 +26,19 @@ def __get_value(item):
                 item = item.view()
             return item.get(key)
 
-        values = set(__get_value(item) for item in self)
+        values = []
+
+        def __append_value(value):
+            if value not in values:
+                values.append(value)
+
+        for item in self:
+            value = __get_value(item)
+            if isinstance(value, list):
+                for v in value:
+                    __append_value(v)
+            else:
+                __append_value(value)
         return list(values)
 
     def view(self, name="defaults"):

tests/__init__.py

@@ -23,7 +23,7 @@ async def test_thingy_list_distinct_thingies():
 
     distinct = foos.distinct("bar")
     assert distinct.count(None) == 1
-    assert set(distinct) == {None, "baz", "qux"}
+    assert distinct == [None, "baz", "qux"]
 
 
 async def test_thingy_list_distinct_dicts():
@@ -35,7 +35,20 @@ async def test_thingy_list_distinct_dicts():
 
     distinct = foos.distinct("bar")
     assert distinct.count(None) == 1
-    assert set(distinct) == {None, "baz", "qux"}
+    assert distinct == [None, "baz", "qux"]
+
+
+# https://mongodb.com/docs/manual/reference/method/db.collection.distinct/#array-fields
+async def test_thingy_list_distinct_array_fields():
+    foos = ThingyList()
+    foos.append(Thingy())
+    foos.append(Thingy())
+    foos.append(Thingy(bar=[1, 2]))
+    foos.append(Thingy(bar=[2, 3, [3]]))
+
+    distinct = foos.distinct("bar")
+    assert distinct.count(None) == 1
+    assert distinct == [None, 1, 2, 3, [3]]
 
 
 async def test_thingy_list_view():