extend 'parent-metadata' functionality (#1687, #1651, #1364)

docs/configuration.rst

@@ -165,11 +165,23 @@ Description
 extractor.*.parent-metadata
 ---------------------------
 Type
-    ``bool``
+    ``bool`` or ``string``
 Default
     ``false``
 Description
-    Overwrite any metadata provided by a child extractor with its parent's.
+    If ``true``, overwrite any metadata provided by a child extractor
+    with its parent's.
+
+    | If this is a ``string``, add a parent's metadata to its children's
+      to a field named after said string.
+    | For example with ``"parent-metadata": "_p_"``:
+
+    .. code:: json
+
+        {
+            "id": "child-id",
+            "_p_": {"id": "parent-id"}
+        }
 
 
 extractor.*.parent-skip

gallery_dl/job.py

@@ -302,11 +302,18 @@ class DownloadJob(Job):
             else:
                 extr._parentdir = pextr._parentdir
 
-            if pextr.config("parent-metadata"):
-                if self.kwdict:
-                    job.kwdict.update(self.kwdict)
-                if kwdict:
-                    job.kwdict.update(kwdict)
+            pmeta = pextr.config("parent-metadata")
+            if pmeta:
+                if isinstance(pmeta, str):
+                    data = self.kwdict.copy()
+                    if kwdict:
+                        data.update(kwdict)
+                    job.kwdict[pmeta] = data
+                else:
+                    if self.kwdict:
+                        job.kwdict.update(self.kwdict)
+                    if kwdict:
+                        job.kwdict.update(kwdict)
 
             if pextr.config("parent-skip"):
                 job._skipcnt = self._skipcnt