Set previous generation when running a backup.

1 files changed, 6 insertions, 1 deletions

diff --git a/obnam/oper_backup.py b/obnam/oper_backup.py
index dd11690f..a9a5240d 100644
--- a/obnam/oper_backup.py
+++ b/obnam/oper_backup.py
@@ -37,7 +37,12 @@ class Backup(obnam.Operation):
         app.get_store().load_maps()
         # We don't need to load in file data, therefore we don't load
         # the content map blocks.
-    
+
+        old_gen_ids = host.get_generation_ids()
+        if old_gen_ids:
+            prev_gen = app.get_store().get_object(old_gen_ids[-1])
+            app.set_previous_generation(prev_gen)
+                
         gen = app.backup(roots)
         
         app.get_store().commit_host_block([gen])