From 6cd33e110eb00074e67e899a156e44e3edd31bdc Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 18 Dec 2017 08:00:18 +0530
Subject: [PATCH] Add a tweak in Preferences->Tweaks to exclude some fields
 when using the Edit metadata->Copy metadata/paste actions

---
 resources/default_tweaks.py               | 7 +++++++
 src/calibre/ebooks/metadata/book/base.py  | 4 ++++
 src/calibre/gui2/actions/edit_metadata.py | 8 +++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/resources/default_tweaks.py b/resources/default_tweaks.py
index 3941cc5663..3233797037 100644
--- a/resources/default_tweaks.py
+++ b/resources/default_tweaks.py
@@ -560,3 +560,10 @@ cover_drop_exclude = ()
 # new Saved search is shown in the Search bar. If you would like to have the
 # old Saved searches box with its two buttons back, set this tweak to True.
 show_saved_search_box = False
+
+#: Exclude fields when copy/pasting metadata
+# You can ask calibre to not paste some metadata fields when using the
+# Edit metadata->Copy metadata/Paste metadata actions. For example,
+# exclude_fields_on_paste = ['cover', 'timestamp', '#mycolumn']
+# to prevent pasting of the cover, Date and custom column, mycolumn.
+exclude_fields_on_paste = []
diff --git a/src/calibre/ebooks/metadata/book/base.py b/src/calibre/ebooks/metadata/book/base.py
index 2c7e84f104..6983637e91 100644
--- a/src/calibre/ebooks/metadata/book/base.py
+++ b/src/calibre/ebooks/metadata/book/base.py
@@ -117,6 +117,10 @@ class Metadata(object):
         except:
             return True
 
+    def set_null(self, field):
+        null_val = copy.copy(NULL_VALUES.get(field))
+        setattr(self, field, null_val)
+
     def __getattribute__(self, field):
         _data = object.__getattribute__(self, '_data')
         if field in SIMPLE_GET:
diff --git a/src/calibre/gui2/actions/edit_metadata.py b/src/calibre/gui2/actions/edit_metadata.py
index 4ae0fcc2f7..ecd703df32 100644
--- a/src/calibre/gui2/actions/edit_metadata.py
+++ b/src/calibre/gui2/actions/edit_metadata.py
@@ -19,6 +19,7 @@ from calibre.gui2.actions import InterfaceAction
 from calibre.ebooks.metadata import authors_to_string
 from calibre.ebooks.metadata.book.base import Metadata
 from calibre.ebooks.metadata.opf2 import OPF, metadata_to_opf
+from calibre.utils.config import tweaks
 from calibre.utils.date import is_date_undefined
 from calibre.utils.icu import sort_key
 from calibre.db.errors import NoSuchFormat
@@ -141,7 +142,12 @@ class EditMetadataAction(InterfaceAction):
         data = bytes(md.data('application/calibre-book-metadata'))
         mi = OPF(BytesIO(data), populate_spine=False, read_toc=False, try_to_guess_cover=False).to_book_metadata()
         mi.application_id = mi.uuid_id = None
-        cover = md.imageData()
+        exclude = set(tweaks['exclude_fields_on_paste'])
+        paste_cover = 'cover' not in exclude
+        cover = md.imageData() if paste_cover else None
+        exclude.discard('cover')
+        for field in exclude:
+            mi.set_null(field)
         db = self.gui.current_db
         book_ids = {db.id(r.row()) for r in rows}
         for book_id in book_ids: