Track snapshot base lineage in Django

README.md

@@ -138,6 +138,8 @@ SQLite remains the default because it is enough for a single backup server and k
 ## Current Architecture
 
 The public command surface is Django-first. The old YAML/cron CLI has been retired from the `pobsync` entrypoint.
+Discovered snapshots are stored in `SnapshotRecord`, including the base snapshot metadata and a nullable SQL link to the
+base record when it is known.
 
 The remaining internal engine code still contains reusable backup primitives:
 
@@ -148,7 +150,6 @@ The remaining internal engine code still contains reusable backup primitives:
 
 Next refactor targets:
 
-- Record discovered snapshots into `SnapshotRecord`.
 - Surface `SnapshotRecord` data through API/admin views instead of filesystem inspection.
 - Move more snapshot lifecycle details into typed domain objects.
 - Replace remaining dictionary-shaped config at engine boundaries.

src/pobsync_backend/admin.py

@@ -58,9 +58,17 @@ class BackupRunAdmin(admin.ModelAdmin):
 
 @admin.register(SnapshotRecord)
 class SnapshotRecordAdmin(admin.ModelAdmin):
-    list_display = ("host", "kind", "dirname", "status", "started_at", "discovered_at")
+    list_display = ("host", "kind", "dirname", "status", "base", "started_at", "discovered_at")
-    list_filter = ("kind", "status", "started_at", "discovered_at")
+    list_filter = ("kind", "status", "base_kind", "started_at", "discovered_at")
-    search_fields = ("host__host", "dirname", "path")
+    search_fields = (
+        "host__host",
+        "dirname",
+        "path",
+        "base__dirname",
+        "base_path",
+        "base_snapshot_id",
+    )
+    autocomplete_fields = ("base",)
     readonly_fields = ("discovered_at",)
 
 

src/pobsync_backend/migrations/0005_snapshotrecord_base.py

@@ -0,0 +1,44 @@
+from __future__ import annotations
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("pobsync_backend", "0004_backuprun_snapshot"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="snapshotrecord",
+            name="base",
+            field=models.ForeignKey(
+                blank=True,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name="derived_snapshots",
+                to="pobsync_backend.snapshotrecord",
+            ),
+        ),
+        migrations.AddField(
+            model_name="snapshotrecord",
+            name="base_dirname",
+            field=models.CharField(blank=True, max_length=255),
+        ),
+        migrations.AddField(
+            model_name="snapshotrecord",
+            name="base_snapshot_id",
+            field=models.CharField(blank=True, max_length=64),
+        ),
+        migrations.AddField(
+            model_name="snapshotrecord",
+            name="base_kind",
+            field=models.CharField(blank=True, max_length=16),
+        ),
+        migrations.AddField(
+            model_name="snapshotrecord",
+            name="base_path",
+            field=models.CharField(blank=True, max_length=1024),
+        ),
+    ]

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)

src/pobsync_backend/snapshot_discovery.py

@@ -55,6 +55,7 @@ def discover_snapshots(
                     created += 1
                 else:
                     updated += 1
+        resolve_base_links(host=host_config)
 
     return {
         "ok": True,
@@ -66,8 +67,15 @@ def discover_snapshots(
 
 def upsert_snapshot_record(*, host: HostConfig, kind: str, snapshot_dir: Path) -> tuple[SnapshotRecord, bool]:
     meta = read_snapshot_meta(snapshot_dir)
+    base_defaults = _base_defaults_from_meta(meta)
     defaults = {
         "path": str(snapshot_dir),
+        **base_defaults,
+        "base": _resolve_base_record(
+            host=host,
+            kind=base_defaults["base_kind"],
+            dirname=base_defaults["base_dirname"],
+        ),
         "status": str(meta.get("status") or ""),
         "started_at": parse_snapshot_datetime(snapshot_dir.name, meta, "started_at"),
         "ended_at": parse_snapshot_datetime(snapshot_dir.name, meta, "ended_at"),
@@ -81,6 +89,26 @@ def upsert_snapshot_record(*, host: HostConfig, kind: str, snapshot_dir: Path) -
     )
 
 
+def resolve_base_links(*, host: HostConfig | None = None) -> int:
+    snapshot_qs = SnapshotRecord.objects.exclude(base_dirname="").filter(base__isnull=True)
+    if host is not None:
+        snapshot_qs = snapshot_qs.filter(host=host)
+
+    updated = 0
+    for snapshot in snapshot_qs.select_related("host"):
+        base = _resolve_base_record(
+            host=snapshot.host,
+            kind=snapshot.base_kind,
+            dirname=snapshot.base_dirname,
+        )
+        if base is None:
+            continue
+        snapshot.base = base
+        snapshot.save(update_fields=["base"])
+        updated += 1
+    return updated
+
+
 def infer_snapshot_kind(snapshot_path: Path) -> str:
     parent = snapshot_path.parent.name
     if parent == "scheduled":
@@ -92,6 +120,29 @@ def infer_snapshot_kind(snapshot_path: Path) -> str:
     raise ValueError(f"Cannot infer snapshot kind from path: {snapshot_path}")
 
 
+def _base_defaults_from_meta(meta: dict[str, Any]) -> dict[str, Any]:
+    base = meta.get("base")
+    if not isinstance(base, dict):
+        base = {}
+
+    return {
+        "base_kind": _base_value(base.get("kind")),
+        "base_dirname": _base_value(base.get("dirname")),
+        "base_path": _base_value(base.get("path")),
+        "base_snapshot_id": _base_value(base.get("id")),
+    }
+
+
+def _base_value(value: Any) -> str:
+    return value if isinstance(value, str) else ""
+
+
+def _resolve_base_record(*, host: HostConfig, kind: str, dirname: str) -> SnapshotRecord | None:
+    if not kind or not dirname:
+        return None
+    return SnapshotRecord.objects.filter(host=host, kind=kind, dirname=dirname).first()
+
+
 def _parse_iso_z(value: str) -> datetime | None:
     try:
         if value.endswith("Z"):

src/pobsync_backend/tests/test_snapshot_discovery.py

@@ -10,7 +10,12 @@ from django.test import TestCase
 
 from pobsync.util import write_yaml_atomic
 from pobsync_backend.models import GlobalConfig, HostConfig, SnapshotRecord
-from pobsync_backend.snapshot_discovery import discover_snapshots, parse_snapshot_datetime
+from pobsync_backend.snapshot_discovery import (
+    discover_snapshots,
+    parse_snapshot_datetime,
+    resolve_base_links,
+    upsert_snapshot_record,
+)
 
 
 class SnapshotDiscoveryTests(TestCase):
@@ -58,6 +63,82 @@ class SnapshotDiscoveryTests(TestCase):
         self.assertEqual(record.kind, "scheduled")
         self.assertEqual(record.started_at, datetime(2026, 5, 19, 2, 15, tzinfo=timezone.utc))
 
+    def test_discovery_links_snapshot_to_base_record(self) -> None:
+        with TemporaryDirectory() as tmp:
+            backup_root = Path(tmp) / "backups"
+            GlobalConfig.objects.create(name="default", backup_root=str(backup_root))
+            host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+            base_dir = backup_root / host.host / "scheduled" / "20260518-021500Z__BASESNAP"
+            child_dir = backup_root / host.host / "scheduled" / "20260519-021500Z__CHILDSNP"
+            (base_dir / "meta").mkdir(parents=True)
+            (child_dir / "meta").mkdir(parents=True)
+            write_yaml_atomic(
+                base_dir / "meta" / "meta.yaml",
+                {
+                    "id": "base-id",
+                    "status": "success",
+                    "started_at": "2026-05-18T02:15:00Z",
+                    "base": None,
+                },
+            )
+            write_yaml_atomic(
+                child_dir / "meta" / "meta.yaml",
+                {
+                    "id": "child-id",
+                    "status": "success",
+                    "started_at": "2026-05-19T02:15:00Z",
+                    "base": {
+                        "kind": "scheduled",
+                        "dirname": base_dir.name,
+                        "id": "base-id",
+                        "path": str(base_dir / "data"),
+                    },
+                },
+            )
+
+            result = discover_snapshots(host=host)
+
+        self.assertEqual(result["created"], 2)
+        child = SnapshotRecord.objects.get(dirname=child_dir.name)
+        base = SnapshotRecord.objects.get(dirname=base_dir.name)
+        self.assertEqual(child.base, base)
+        self.assertEqual(child.base_kind, "scheduled")
+        self.assertEqual(child.base_dirname, base_dir.name)
+        self.assertEqual(child.base_snapshot_id, "base-id")
+        self.assertEqual(child.base_path, str(base_dir / "data"))
+
+    def test_base_link_can_be_resolved_after_base_record_exists(self) -> None:
+        with TemporaryDirectory() as tmp:
+            backup_root = Path(tmp) / "backups"
+            host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+            base_dir = backup_root / host.host / "scheduled" / "20260518-021500Z__BASESNAP"
+            child_dir = backup_root / host.host / "scheduled" / "20260519-021500Z__CHILDSNP"
+            (base_dir / "meta").mkdir(parents=True)
+            (child_dir / "meta").mkdir(parents=True)
+            write_yaml_atomic(base_dir / "meta" / "meta.yaml", {"status": "success"})
+            write_yaml_atomic(
+                child_dir / "meta" / "meta.yaml",
+                {
+                    "status": "success",
+                    "base": {
+                        "kind": "scheduled",
+                        "dirname": base_dir.name,
+                        "id": "base-id",
+                        "path": str(base_dir / "data"),
+                    },
+                },
+            )
+
+            child, _created = upsert_snapshot_record(host=host, kind="scheduled", snapshot_dir=child_dir)
+            upsert_snapshot_record(host=host, kind="scheduled", snapshot_dir=base_dir)
+            linked = resolve_base_links(host=host)
+
+        child.refresh_from_db()
+        self.assertEqual(linked, 1)
+        self.assertIsNotNone(child.base)
+        self.assertEqual(child.base.dirname, base_dir.name)
+        self.assertEqual(child.base_dirname, base_dir.name)
+
     def test_command_discovers_snapshots_for_host(self) -> None:
         with TemporaryDirectory() as tmp:
             backup_root = Path(tmp) / "backups"