TP2000-1600 Add Subtask filter to Task admin view

tasks/admin.py

@@ -29,10 +29,29 @@ def link_to_workbasket(self, workbasket):
         )
 
 
+class SubtaskFilter(admin.SimpleListFilter):
+    title = "Subtasks"
+    parameter_name = "is_subtask"
+
+    def lookups(self, request, model_admin):
+        return (
+            ("TRUE", "Subtasks"),
+            ("FALSE", "Tasks"),
+        )
+
+    def queryset(self, request, queryset):
+        value = self.value()
+        if value == "TRUE":
+            return queryset.subtasks()
+        elif value == "FALSE":
+            return queryset.parents()
+
+
 class TaskAdmin(TaskAdminMixin, admin.ModelAdmin):
     list_display = [
         "id",
         "title",
+        "is_subtask",
         "description",
         "category",
         "progress_state",
@@ -41,7 +60,11 @@ class TaskAdmin(TaskAdminMixin, admin.ModelAdmin):
         "creator",
     ]
     search_fields = ["id", "title", "description"]
-    list_filter = ["category", "progress_state"]
+    list_filter = (
+        SubtaskFilter,
+        "category",
+        "progress_state",
+    )
 
     def parent_task_id(self, obj):
         if not obj.parent_task:

tasks/models/task.py

@@ -1,6 +1,7 @@
 from datetime import datetime
 
 from django.conf import settings
+from django.contrib import admin
 from django.contrib.auth import get_user_model
 from django.db import models
 from django.db import transaction
@@ -74,6 +75,17 @@ def top_level(self):
             models.Q(taskitem__isnull=True) | models.Q(taskworkflow__isnull=False),
         )
 
+    def parents(self):
+        """Returns a queryset of tasks who do not have subtasks linked to
+        them."""
+        return self.filter(
+            models.Q(parent_task=None),
+        )
+
+    def subtasks(self):
+        """Returns a queryset of tasks who have parent tasks linked to them."""
+        return self.exclude(models.Q(parent_task=None))
+
 
 class TaskBase(TimestampedMixin):
     """Abstract model mixin containing model fields common to TaskTemplate and
@@ -122,6 +134,7 @@ class Task(TaskBase):
     objects = TaskManager.from_queryset(TaskQueryset)()
 
     @property
+    @admin.display(boolean=True)
     def is_subtask(self) -> bool:
         return bool(self.parent_task)