Case insensitive data fetch (DTLfetch) with package datatool

Question

In one of my setup, I'm making simple setup for my users, meaning that most of the strings are saved in a data tool DB, and they can retrieve it by activating a command.

So I've created simple hardcoded key-value model in a defined DB. Now I've got an issue with Datatool, as I'd like that my "keys" to be case-insensitive. I don't want to debug in case a user select "sp" or "Sp" instead of "SP". This is simpler for me to spend some time on input validation.

However, my MWE belo is throwing a bunch of error (among others "Undefined sequence"). What am I doing wrong ?

\documentclass{article}
\usepackage{datatool}

\DTLnewdb{dbSemester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SP}
\DTLnewdbentry{dbSemester}{value}{Spring semester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SA}
\DTLnewdbentry{dbSemester}{value}{Autumn semester}

\newcommand{\getSemester}[1]{%
    \DTLfetch{dbSemester}{key}{\MakeUppercase{#1}}{value}
}


\begin{document}
    \getSemester{sa}
    \getSemester{SP}
\end{document}

Update 20/08/2018

I found some answers here and there, about some formatting of the output produced by DTLfetch, but nothing related to passing a non expandable parameters to the DTLfetch command. I'm starting to believe that this is not poassible to achieve.

Otherwise, I've thought of a potential workaround would be to add the uppercase version inside of the table and to duplicate the entries

Answer 1

The issue is that typical upper-case macros in LaTeX are not expandable.

See Expandably change letter case and use inside \csname, without a package

\documentclass{article}
\usepackage{datatool,stringstrings}

\DTLnewdb{dbSemester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SP}
\DTLnewdbentry{dbSemester}{value}{Spring semester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SA}
\DTLnewdbentry{dbSemester}{value}{Autumn semester}

\newcommand{\getSemester}[1]{%
    \caseupper[q]{#1}%
    \def\tmpA{\DTLfetch{dbSemester}{key}}%
    \expandafter\tmpA\expandafter{\thestring}{value}
}
\begin{document}
    \getSemester{sa}
    \getSemester{SP}
\end{document}

Here's a version without the use of stringstrings, based on methods provided in the cited question:

\documentclass{article}
\usepackage{datatool}

\def\expupperchar#1{%
  \ifcase\numexpr`#1-`a\relax
   A\or B\or C\or D\or E\or F\or G\or H\or I\or J\or K\or L\or M\or
   N\or O\or P\or Q\or R\or S\or T\or U\or V\or W\or X\or Y\or Z\else
   #1\fi
}

\def\expupper#1{%
  \doexpupperchar#1\relax
}

\def\doexpupperchar#1{%
  \ifx#1\relax
  \else
    \expupperchar{#1}\expandafter\doexpupperchar
  \fi
}

\DTLnewdb{dbSemester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SP}
\DTLnewdbentry{dbSemester}{value}{Spring semester}
\DTLnewrow{dbSemester}
\DTLnewdbentry{dbSemester}{key}{SA}
\DTLnewdbentry{dbSemester}{value}{Autumn semester}

\newcommand{\getSemester}[1]{%
    \edef\thestring{\expupper{#1}}%
    \def\tmpA{\DTLfetch{dbSemester}{key}}%
    \expandafter\tmpA\expandafter{\thestring}{value}
}
\begin{document}
    \getSemester{sa}
    \getSemester{SP}
\end{document}