Ongoing development of "Things"

boxes/models.py

@@ -1,4 +1,5 @@
 from django.db import models
+from mptt.models import MPTTModel, TreeForeignKey
 
 
 class BoxType(models.Model):
@@ -37,13 +38,20 @@ class Box(models.Model):
         return self.id
 
 
-class ThingType(models.Model):
-    """A type/category for things stored in boxes."""
+class ThingType(MPTTModel):
+    """A hierarchical type/category for things stored in boxes."""
 
-    name = models.CharField(max_length=255, unique=True)
+    name = models.CharField(max_length=255)
+    parent = TreeForeignKey(
+        'self',
+        on_delete=models.CASCADE,
+        null=True,
+        blank=True,
+        related_name='children'
+    )
 
-    class Meta:
-        ordering = ['name']
+    class MPTTMeta:
+        order_insertion_by = ['name']
 
     def __str__(self):
         return self.name