Add command to backpopulate file_id field

This can be removed once we've deployed and successfully migrated the
existing data.

local_db/management/commands/backpopulate_file_id.py

@@ -0,0 +1,18 @@
+from django.core.management.base import BaseCommand
+
+from airlock.business_logic import bll, store_file
+from local_db.models import RequestFileMetadata
+
+
+class Command(BaseCommand):
+    def handle(self, **kwargs):
+        empty_file_ids = RequestFileMetadata.objects.filter(file_id="")
+        for file_meta in list(empty_file_ids):
+            request_id = file_meta.filegroup.request_id
+            request = bll.get_release_request(request_id)
+            original_path = (
+                request.root() / file_meta.filegroup.name / file_meta.relpath
+            )
+            file_meta.file_id = store_file(request, original_path)
+            file_meta.save()
+            original_path.unlink()

tests/integration/management/commands/test_backpopulate_file_id.py

@@ -0,0 +1,39 @@
+import pytest
+from django.core.management import call_command
+
+from local_db.models import RequestFileMetadata
+from tests import factories
+
+
+@pytest.mark.django_db
+def test_command():
+    # Create a ReleaseRequest with a single file
+    factories.write_workspace_file("workspace", "subdir/file.txt", "some content")
+    release_request = factories.create_release_request("workspace")
+    factories.create_filegroup(
+        release_request, group_name="default_group", filepaths=["subdir/file.txt"]
+    )
+
+    # Determine its current path and its "old style" path
+    file_meta = RequestFileMetadata.objects.get()
+    full_relpath = f"{file_meta.filegroup.name}/{file_meta.relpath}"
+    path_with_hash = release_request.abspath(full_relpath)
+    old_style_path = release_request.root() / full_relpath
+
+    # Move the file to its old location
+    old_style_path.parent.mkdir(parents=True, exist_ok=True)
+    path_with_hash.rename(old_style_path)
+
+    # Remove the file hash from the database record
+    file_meta.file_id = ""
+    file_meta.save()
+
+    call_command("backpopulate_file_id")
+
+    # Confirm the database record now contains a hash
+    file_meta = RequestFileMetadata.objects.get()
+    assert file_meta.file_id != ""
+
+    # Confirm that the file is in its expected location and not in its old location
+    assert path_with_hash.exists()
+    assert not old_style_path.exists()