diff --git a/swh/provenance/model.py b/swh/provenance/model.py
--- a/swh/provenance/model.py
+++ b/swh/provenance/model.py
@@ -35,6 +35,12 @@
             )
         return (x for x in self._revisions)
 
+    def __str__(self):
+        return (
+            f"<MOrigin[{self.url}] "
+            f"snap={self.snapshot.hex()}, date={self.date.isoformat()}>"
+        )
+
 
 class RevisionEntry:
     def __init__(
@@ -48,29 +54,43 @@
         self.date = date
         assert self.date is None or self.date.tzinfo is not None
         self.root = root
-        self._parents = parents
-        self._nodes: List[RevisionEntry] = []
-
-    def parents(self, archive: ArchiveInterface):
-        if self._parents is None:
-            revision = list(archive.revision_get([self.id]))
-            if revision:
-                self._parents = revision[0].parents
-        if self._parents and not self._nodes:
-            self._nodes = [
+        self._parents_ids = parents
+        self._parents_entries: Optional[List[RevisionEntry]] = None
+
+    def retrieve_parents(self, archive: ArchiveInterface):
+        if self._parents_entries is None:
+            if self._parents_ids is None:
+                revision = list(archive.revision_get([self.id]))
+                if revision:
+                    self._parents_ids = revision[0].parents
+                else:
+                    self._parents_ids = []
+
+            self._parents_entries = [
                 RevisionEntry(
                     id=rev.id,
                     root=rev.directory,
                     date=rev.date.to_datetime(),
                     parents=rev.parents,
                 )
-                for rev in archive.revision_get(self._parents)
+                for rev in archive.revision_get(self._parents_ids)
                 if rev.date is not None
             ]
-        yield from self._nodes
+
+    @property
+    def parents(self) -> Iterator["RevisionEntry"]:
+        if self._parents_entries is None:
+            raise RuntimeError(
+                "Parents of this node has not yet been retrieved. "
+                "Please call retrieve_parents() before using this property."
+            )
+        return (x for x in self._parents_entries)
 
     def __str__(self):
-        return f"<MRevision[{self.id.hex()}] {self.date.isoformat()}>"
+        return (
+            f"<MRevision[{self.id.hex()}] "
+            f"date={self.date.isoformat()}, root={self.root.hex()}>"
+        )
 
 
 class DirectoryEntry:
diff --git a/swh/provenance/origin.py b/swh/provenance/origin.py
--- a/swh/provenance/origin.py
+++ b/swh/provenance/origin.py
@@ -96,7 +96,8 @@
         else:
             # This revision is a parent of another one in the history of the
             # relative revision.
-            for parent in current.parents(archive):
+            current.retrieve_parents(archive)
+            for parent in current.parents:
                 visited = provenance.revision_visited(parent)
 
                 if not visited: