After renaming a custom Magneto 2 theme folder, to correct a capitalisation mistake, I ran into all sorts of issues, starting with this error:
Required parameter ‘theme_dir’ was not passed
After reading around I removed the entry from the database table “themes” and tried to set any pages or stores set to use that theme to use something else. Then I endlessly got this:
Error – Exception #0 (LogicException): Unable to load theme by specified key: ‘4’
ID 4 was the id of the theme I removed from the DB.
When trying to change the theme configuration in the Admin I would be presented with
Something went wrong while saving this configuration: Unable to load theme by specified key: ‘4’
In the end I searched through some likely looking database tables to look for theme references.
The first was an entry in the core_config_data table, found by doing SELECT * FROM [magento2].core_config_data WHERE path LIKE ‘%theme%’; There I saw an entry with design/theme/theme_id 4 . Changed that to that of another theme.
There was also a reference to the rogue id in the design_config_grid_flat table and also one in the cms_page table.
Sorting all these out sorted the error….phew…