Track snapshot base lineage in Django

src/pobsync_backend/models.py

@@ -111,6 +111,17 @@ class SnapshotRecord(models.Model):
     kind = models.CharField(max_length=16, choices=Kind.choices)
     dirname = models.CharField(max_length=255)
     path = models.CharField(max_length=1024)
+    base = models.ForeignKey(
+        "self",
+        on_delete=models.SET_NULL,
+        null=True,
+        blank=True,
+        related_name="derived_snapshots",
+    )
+    base_kind = models.CharField(max_length=16, blank=True)
+    base_dirname = models.CharField(max_length=255, blank=True)
+    base_path = models.CharField(max_length=1024, blank=True)
+    base_snapshot_id = models.CharField(max_length=64, blank=True)
     status = models.CharField(max_length=32, blank=True)
     started_at = models.DateTimeField(null=True, blank=True)
     ended_at = models.DateTimeField(null=True, blank=True)