Add MultiSelectRelatedFieldListFilter

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "django-admin-multi-select-filter"
-version = "1.1.0"
+version = "1.2.0"
 description = "Django admin filter for multiple select"
 readme = "README.md"
 authors = [{ name = "Job Doesburg", email = "[email protected]" }]

src/django_admin_multi_select_filter/filters.py

@@ -20,13 +20,12 @@ def __init__(self, field, request, params, model, model_admin, field_path):
         # Obey parent ModelAdmin queryset when deciding which options to show
         if model == parent_model:
             queryset = model_admin.get_queryset(request)
-            self.lookup_choices = (
-                queryset.distinct().order_by(field.name).values_list(field.name, flat=True)
-            )
         else:
             queryset = parent_model._default_manager.all()
-            self.lookup_choices = queryset.distinct()
-
+        self.lookup_choices = (
+            queryset.distinct().order_by(field.name).values_list(field.name, flat=True)
+        )
+
     def expected_parameters(self):
         return [self.lookup_kwarg, self.lookup_kwarg_isnull]
 
@@ -76,3 +75,51 @@ def choices(self, changelist):
                 ),
                 "display": self.empty_value_display,
             }
+
+
+class MultiSelectRelatedFieldListFilter(admin.RelatedFieldListFilter):
+    def __init__(self, field, request, params, model, model_admin, field_path):
+        super().__init__(field, request, params, model, model_admin, field_path)
+        self.lookup_kwarg = "%s__%s__in" % (field_path, field.target_field.name)
+        self.lookup_kwarg_isnull = "%s__isnull" % field_path
+        values = params.get(self.lookup_kwarg, [])
+        self.lookup_val = values.split(",") if values else []
+        self.lookup_choices = self.field_choices(field, request, model_admin)
+
+    def choices(self, changelist):
+        yield {
+            "selected": self.lookup_val is None and not self.lookup_val_isnull,
+            "query_string": changelist.get_query_string(
+                remove=[self.lookup_kwarg, self.lookup_kwarg_isnull]
+            ),
+            "display": _("All"),
+        }
+
+        for pk_val, val in self.lookup_choices:
+            if val is None:
+                self.include_empty_choice = True
+                continue
+            val = str(val)
+
+            if str(pk_val) in self.lookup_val:
+                values = [str(v) for v in self.lookup_val if str(v) != str(pk_val)]
+            else:
+                values = self.lookup_val + [str(pk_val)]
+
+            yield {
+                "selected": self.lookup_val is not None
+                and str(pk_val) in self.lookup_val,
+                "query_string": changelist.get_query_string(
+                    {self.lookup_kwarg: ",".join(values)}, [self.lookup_kwarg_isnull]
+                ),
+                "display": val,
+            }
+        empty_title = self.empty_value_display
+        if self.include_empty_choice:
+            yield {
+                "selected": bool(self.lookup_val_isnull),
+                "query_string": changelist.get_query_string(
+                    {self.lookup_kwarg_isnull: "True"}, [self.lookup_kwarg]
+                ),
+                "display": empty_title,
+            }