Suggestion for \cite in Emacs with AUCTeX

Question

I would like to know how can I get the suggestion when I do a \\cite in Emacs-AUCTeX. The minibuffer tells me when I do C-c [ that:

No valid bibliography

Answer 1

When in the buffer of your non-master file, try to query for the name of a master file (again) with C-c _ (Control C + underscore) as explained in auctex manual

This will add the local variable TeX-master to the end of your file. Save your file, restart emacs and load your file again. Hopefully, you can now get references from the bibliography stated in your master file by calling C-c [ in the subfile.

Mysteriously, when I do this manually without letting auctex query for it, it does not work. I cannot see how the end result is different in the auto directory either. But somehow letting auctex query for the value made it work for me.