[chaley]

It works for me, of course. These 'sometimes' problems are a big pain.

What I did:

• Updated to latest source.
• Created an empty configuration directory to remove any possible plugin influence.
• Created a library containing your metadata.db
• Ran calibre, which went through the welcome wizard. I pointed it at the library containing your database.
• Your aamy_ifempty() function was there.
• I created a composite column calling your function. It shows the correct value.

To help trace this down I added some logging to calibre.db.backend.py. The source file is attached.

Here is the log when I ran it:

Spoiler:

c:\CBH_Data\calibre.git>test_calibre_temp.bat
c:\CBH_Data\calibre.git>set CALIBRE_CONFIG_DIRECTORY=C:\CBH_Data\calibre.git\config_test_temp
c:\CBH_Data\calibre.git>"c:\Program Files\calibre2\calibre-debug" -g

calibre 6.0*  embedded-python: True
Windows-10-10.0.19044 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19044')
Python 3.10.1
Windows: ('10', '10.0.19044', '', 'Multiprocessor Free')
Interface language: en_GB
devicePixelRatio: 1.0
logicalDpi: 96.0 x 96.0
physicalDpi: 86.46808510638297 x 86.41063122923588
Using calibre Qt style: True
[0.00] Starting up...
[0.00] Showing splash screen...
[0.20] splash screen shown
[0.20] Initializing db...
backend.__init__ - set template functions aamy_ifempty
backend.set_user_template_functions 1 aamy_ifempty
backend.set_user_template_functions 2 add, and, approximate_formats, arguments, assign, author_links, author_sorts, book_count, book_values, booksize, capitalize, character, check_yes_no, ceiling, cmp, connected_device_name, connected_device_uuid, contains, count, list_count, current_library_name, current_library_path, current_virtual_library_name, date_arithmetic, days_between, divide, eval, first_non_empty, field, field_exists, finish_formatting, first_matching_cmp, floor, format_date, format_number, formats_modtimes, formats_paths, formats_sizes, fractional_part, globals, has_cover, human_readable, identifier_in_list, ifempty, language_codes, language_strings, in_list, list_contains, is_marked, list_count_matching, count_matching, list_difference, list_equals, list_intersection, list_item, list_join, list_re, list_re_group, list_remove_duplicates, list_sort, list_split, list_union, merge_lists, lookup, lowercase, mod, multiply, not, ondevice, or, print, rating_to_stars, range, raw_field, raw_list, re, re_group, round, select, series_sort, set_globals, shorten, strcat, strcat_max, strcmp, str_in_list, strlen, subitems, sublist, substr, subtract, swap_around_articles, swap_around_comma, switch, template, test, titlecase, today, transliterate, uppercase, urls_from_identifiers, user_categories, virtual_libraries, annotation_count, aamy_ifempty
backend.get_user_template_functions aamy_ifempty
backend.set_global_state aamy_ifempty
backend.get_user_template_functions aamy_ifempty
[0.20] db initialized
[0.20] Constructing main UI...
backend.get_template_functions add, and, approximate_formats, arguments, assign, author_links, author_sorts, book_count, book_values, booksize, capitalize, character, check_yes_no, ceiling, cmp, connected_device_name, connected_device_uuid, contains, count, list_count, current_library_name, current_library_path, current_virtual_library_name, date_arithmetic, days_between, divide, eval, first_non_empty, field, field_exists, finish_formatting, first_matching_cmp, floor, format_date, format_number, formats_modtimes, formats_paths, formats_sizes, fractional_part, globals, has_cover, human_readable, identifier_in_list, ifempty, language_codes, language_strings, in_list, list_contains, is_marked, list_count_matching, count_matching, list_difference, list_equals, list_intersection, list_item, list_join, list_re, list_re_group, list_remove_duplicates, list_sort, list_split, list_union, merge_lists, lookup, lowercase, mod, multiply, not, ondevice, or, print, rating_to_stars, range, raw_field, raw_list, re, re_group, round, select, series_sort, set_globals, shorten, strcat, strcat_max, strcmp, str_in_list, strlen, subitems, sublist, substr, subtract, swap_around_articles, swap_around_comma, switch, template, test, titlecase, today, transliterate, uppercase, urls_from_identifiers, user_categories, virtual_libraries, annotation_count, aamy_ifempty
[1.22] main UI initialized...
[1.22] Hiding splash screen
Starting QuickView
[1.50] splash screen hidden
[1.50] Started up in 1.50 seconds with 1 books
backend.close - unloading template functions 32d3fa1c-9a4a-450a-a422-e0dcface23d5

c:\CBH_Data\calibre.git>

To make sure we are running the same thing, I am attaching my configuration folder (zipped), the library folder (zipped).