Field in database with several values

I have a database on Nocobase with books. I have a field “subject”. Usually books have several subjects. What kind of field admits several values? (A multiple select is not good because I don’t have a list of subjects, I need to enter then manually in every case).

Thank you!

Create a book table, a book topic table, add a new many-to-many relationship field in the book table associated with the book topic table, set the components of the relationship field in the form as a subform, add multiple topic content

Thank you for the reply.
I was hoping there was a simpler way, but that will have to work.