Biblatex: Change the order of the 'prenote' field

Question

I'm trying to change the order of \footcite using biblatex only for a specific entrytype. For example if I'd try to do that for the \ifentrytype{commentary}, how can I achieve that. I want the following order:

shorthand, prenote, postnote

My idea so war was to change the position of \usebibmacro{prenote} in \DeclareCiteCommand{\footcite}

See attached Example:

\documentclass[12pt,ngerman]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
%
\usepackage[%
citestyle=authoryear,%
bibstyle=authortitle,%
backend=biber%
]{biblatex}
%
\usepackage{lipsum}
\usepackage{fontspec}
\setmainfont{Times New Roman}
%
\usepackage{verbatim}
% =======================================================
% =======================================================
\DeclareBibliographyDriver{commentary}{%
  \usebibmacro{bibindex}%
  \usebibmacro{begentry}%
  \usebibmacro{author/editor+others/translator+others}%
  \setunit{\printdelim{nametitledelim}}\newblock
  \usebibmacro{maintitle+title}%
  \newunit\newblock
  \usebibmacro{byauthor}%
  \newunit\newblock
  \usebibmacro{byeditor+others}%
  \newunit\newblock
  \printfield{edition}
  \newunit
  \usebibmacro{location+date}%
  \newunit\newblock
  \usebibmacro{finentry}}
% =======================================================
\AtEveryCite{
\ifentrytype{commentary}{%
\DeclareCiteCommand{\footcite}%
  %{\usebibmacro{prenote}}% OLD
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}}
   {\usebibmacro{prenote}}% NEW moved the prenote
  {\multicitedelim}
  {\usebibmacro{postnote}}
}{}%
}
% =======================================================
% =======================================================
% =======================================================

\addbibresource{\jobname.bib}
%
\begin{filecontents}{\jobname.bib}
    @commentary{citekey,
    maintitle={M{\"u}nchener Kommentar zum B{\"u}rgerlichen Gesetzbuch},
    editor={S{\"a}cker, Franz},
    volume={1},
    title={Allgemeiner Teil},
    edition={7},
    address={M{\"u}nchen},
    year={2015},
    shorthand={M{\"u}nchKomm},
}
\end{filecontents}

\begin{document}
% =======================================================

% =======================================================
The idea was to just change the position of \verb|\usebibmacro{prenote}|
\footcite[Armbrüster][§ 138 Rn. 11]{citekey}\\
But sadly it doesn't change anything.


\printbibliography[title=Bibliography]
\end{document}

Any idea how to achieve an order like shown on the picture?

Answer 1

The \AtEveryCite doesn't really work because you can't redefine the citation command at a point where you are already executing it. So the redefinition has to happen outside of \AtEveryCite.

On the other hand, \ifentrytype must be executed at a point where the entry type of the processed entry is known. This is not the case if we just do \ifentrytype{commentary}{...redefine \footcite here...}{...keep the original definition...}, so that can't work either. A possible solution is

\DeclareCiteCommand{\footcite}%
  {\ifentrytype{commentary}{}{\usebibmacro{prenote}}}
  {\usebibmacro{citeindex}%
   \usebibmacro{cite}%
   \ifentrytype{commentary}{\usebibmacro{prenote}}{}}
  {\multicitedelim}
  {\usebibmacro{postnote}}

But then you can't add real pre-notes to @commentary types. So I think the idea of abusing the prenote argument in this way is conceptually flawed.

Instead you could think about a solution similar to Optional argument within another optional argument in biblatex \cite. The idea is not to abuse the prenote argument, instead another optional value can be passed to the command via the postnote in round brackets: \autocite[(Armbrüster)§ 138 Rn. 11]{citekey}.

\documentclass[12pt,ngerman]{scrartcl}
\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[
  citestyle=authoryear,
  bibstyle=authortitle,
  backend=biber,
  autocite=footnote,
]{biblatex}

\DeclareBibliographyDriver{commentary}{%
  \usebibmacro{bibindex}%
  \usebibmacro{begentry}%
  \usebibmacro{author/editor+others/translator+others}%
  \setunit{\printdelim{nametitledelim}}\newblock
  \usebibmacro{maintitle+title}%
  \newunit\newblock
  \usebibmacro{byauthor}%
  \newunit\newblock
  \usebibmacro{byeditor+others}%
  \newunit\newblock
  \printfield{edition}
  \newunit
  \usebibmacro{location+date}%
  \newunit\newblock
  \usebibmacro{finentry}}

\addbibresource{\jobname.bib}
\addbibresource{biblatex-examples.bib}

%\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@commentary{citekey,
  maintitle  = {Münchener Kommentar zum Bürgerlichen Gesetzbuch},
  editor     = {Säcker, Franz},
  volume     = {1},
  title      = {Allgemeiner Teil},
  edition    = {7},
  address    = {München},
  year       = {2015},
  shorthand  = {MünchKomm},
}
\end{filecontents}

\let\oldpostnotedelim\postnotedelim
\renewcommand*{\postnotedelim}{\ifentrytype{commentary}{}{\oldpostnotedelim}}
\DeclareFieldFormat{postnote:stem}{\oldpostnotedelim\mkpageprefix[pagination][\mknormrange]{#1}}
\DeclareFieldFormat{postnote:prefix}{\addslash\mkbibemph{#1}}
\DeclareFieldFormat{postnote}{\mkpostnote{#1}}

\makeatletter
\newrobustcmd*{\mkpostnote}[1]{\mkpostnote@i#1&}

\def\mkpostnote@i{%
  \@ifnextchar(%)
    {\mkpostnote@ii}
    {\mkpostnote@ii()}}

\def\mkpostnote@ii(#1)#2&{%
  \ifblank{#1}{}{%
    \blx@getformat\cbx@postnote@prefix@fmt{ffd}{}{postnote:prefix}%
    \cbx@postnote@prefix@fmt{#1}}%
  \ifblank{#2}{}{%
    \blx@getformat\cbx@postnote@stem@fmt{ffd}{}{postnote:stem}%
    \cbx@postnote@stem@fmt{#2}}%
  }
\def\cbx@postnote@stem@fmt{}
\def\cbx@postnote@prefix@fmt{}
\makeatother

\begin{document}
Lorem\autocite[(Armbrüster)§ 138 Rn. 11]{citekey}
ipsum\autocite[cf.][380]{sigfridsson}
dolor\autocite[cf.][(Armbrüster)§ 138 Rn. 11]{citekey}
sit\autocite[cf.][§ 138 Rn. 11]{citekey}
sit\autocite[(Armbrüster)]{citekey}
\printbibliography[title=Bibliography]
\end{document}