Prepending symbols to biblatex-chicago bibliography by keyword

Question

Following on from this question, I would like to prepend a symbol to selected entries in my bibliography. But I would like to match the functionality here where the symbol is inserted automatically based on keywords in the .bbl file.

I can achieve the desired output by uncommenting the two lines in the MWE which does the job manually:

It'd be much more efficient for my workflow if I could use keywords instead.

As far as I can work out, this MWE does not acknowledge the presence of asterisk in the keywords field, even though I've tried to follow the logic in the above links:

\documentclass[american]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber,
  bibencoding=utf8]{biblatex-chicago}
\begin{filecontents}{\jobname.bib}
@book{uthor,
  author        = {Uthor, Arnold},
  title         = {A Book},
  date          = {2013},
  location      = {Place},
  publisher     = {P. Ublisher's & Co.},
  keywords      = {asterisk}
}
\end{filecontents}
\addbibresource{\jobname.bib}
%\DeclareBibliographyCategory{asterisk}
\renewbibmacro{bibindex}{%
  \ifbibindex
    {\indexnames{labelname}%
     \indexfield{indextitle}}
    {}
  \ifcategory{asterisk}%
    {}%
    {}%
}
\begin{document}
%  \addtocategory{asterisk}{uthor}
  \cite{uthor}
  \printbibliography
\end{document}

Please can someone let me know where I'm going wrong?

Answer 1

The solution I see is to use the \ifkeyword test. I prefer to use xpatch in similar cases:

\usepackage{xpatch}
\AtEveryBibitem{\ifkeyword{asterisk}%
 {\xapptobibmacro{bibindex}{*}{}{}}
 {}}

but you can also do without it if you prefer:

\renewbibmacro*{bibindex}{%
 \ifbibindex
 {\indexnames{labelname}%
  \indexfield{indextitle}}
 {}
\ifkeyword{asterisk}{*}{}%
}

MWE

\documentclass[american]{article}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber,
bibencoding=utf8]{biblatex-chicago}
\begin{filecontents}{\jobname.bib}
 @book{uthor,
  author        = {Uthor, Arnold},
  title         = {A Book},
  date          = {2013},
  location      = {Place},
  publisher     = {P. Ublisher's & Co.},
  keywords      = {asterisk}
 }
\end{filecontents}
\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}
\usepackage{xpatch}
\xapptobibmacro{bibindex}{\ifkeyword{asterisk}{*}{}}{}{}
\begin{document}
\paragraph{An entry with “asterisk” keyword}
 \cite{uthor}
\paragraph{An entry without “asterisk” keyword} 
 \cite{knuth:ct}
\printbibliography
\end{document}