create a hyperlink by using the url stored in the bibliography reference?

Question

im wondering if i can create a hyperlink that automaticaly uses the bib file stored tag 'url' somehow? Just to prevent mistakes in linking to a reference and to a websource in the same text like:

mwe:

\documentclass{article}
\usepackage{filecontents}
\usepackage[style=nature, url=true]{biblatex}
\usepackage{hyperref}
\begin{filecontents}{\jobname.bib}
@online{UseCase20,
  title = {{Use-Case 2.0 ebook}},
  journal = {Ivar Jacobson International},
  year = {2014},
  month = {Jul},
  note = {[Online; accessed 25. Dec. 2018]},
  url = {https://www.ivarjacobson.com/publications/white-papers/use-case-ebook}
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
\href{https://www.ivarjacobson.com/publications/white-papers/use-case-ebook}{sometext} \footcite{UseCase20}
\printbibliography
\end{document}

i wold like to something like this work:

\documentclass{article}
\usepackage{filecontents}
\usepackage[style=nature, url=true]{biblatex}
\usepackage{hyperref}
\begin{filecontents}{\jobname.bib}
@online{UseCase20,
  title = {{Use-Case 2.0 ebook}},
  journal = {Ivar Jacobson International},
  year = {2014},
  month = {Jul},
  note = {[Online; accessed 25. Dec. 2018]},
  url = {https://www.ivarjacobson.com/publications/white-papers/use-case-ebook}
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
\href{\citeurl{UseCase20}}{sometext} \footcite{UseCase20}
\printbibliography
\end{document}

but unfortunately this breaks at l.18;

\href{\citeurl{UseCase20}}{sometext}

EDIT:

MWE with all tests:

\documentclass{article}
\usepackage{filecontents}
\usepackage[style=nature, url=true]{biblatex}
\usepackage{hyperref}
\begin{filecontents}{\jobname.bib}
@online{UseCase20,
    title = {{Use-Case 2.0 ebook}},
    journal = {Ivar Jacobson International},
    year = {2014},
    month = {Jul},
    note = {[Online; accessed 25. Dec. 2018]},
    url = {https://www.ivarjacobson.com/publications/white-papers/use-case-ebook}
}
\end{filecontents}
\addbibresource{\jobname.bib}
%https://tex.stackexchange.com/a/413372/118709
\DeclareCiteCommand{\citelink}
    {\boolfalse{citetracker}%
        \boolfalse{pagetracker}%
        \usebibmacro{prenote}}
    {\iffieldundef{postnote}
        {\href{\thefield{url}}{\printfield{title}}}
        {\href{\thefield{url}}{\thefield{postnote}}}}
    {\multicitedelim}
    {}
% https://tex.stackexchange.com/a/412927/118709
\DeclareCiteCommand{\citeqrurl}
  {\boolfalse{citetracker}%
   \boolfalse{pagetracker}%
   \usebibmacro{prenote}}
  {\qrcode{\thefield{url}}}
  {\multicitedelim}
  {\usebibmacro{postnote}}
% https://tex.stackexchange.com/a/413519/118709
\DeclareCiteCommand{\geturl}
    {\boolfalse{citetracker}\boolfalse{pagetracker}}
    {\iffieldundef{postnote}
        {\xdef\biburl{\thefield{url}}}
        {%
            \edef\geturlTmpCmd{\csfield{postnote}}%
            \expandafter\xdef\geturlTmpCmd{\thefield{url}}%
        }%
    }
    {}
    {}
\begin{document}
~\\
\citelink{sometext}{UseCase20}\footcite{UseCase20}\\
~\\
\citeqrurl{sometext}{UseCase20}\footcite{UseCase20}\\
~\\
\geturl{UseCase20}
%The \href{\biburl}{UseCase}\footcite{UseCase20}\\.
\printbibliography
\end{document}

Answer 1

\citeurl does not return the URL of the entry in question (in an expandable way), instead it is meant to print the formatted URL. That means that it can't be used as the URI argument for \href. If you want to be able to \href the URL of an entry to arbitrary text, the simplest way is to create a new \cite... macro. Since \cite... macros have a fixed argument structure the one below works as follows

\citehrefurl[<arbitrary text that is going ot be linked>]{<entrykey>}

You could create a new command with arbitrary arguments. Usually I strongly advise against creating new commands from \cite... commands via \newcommand, but in this case we can make an exception.

\documentclass{article}
\usepackage[style=nature, url=true]{biblatex}
\usepackage{hyperref}

\DeclareCiteCommand{\citehrefurl}
  {\boolfalse{citetracker}%
   \boolfalse{pagetracker}}
  {\iffieldundef{url}
     {\PackageWarning{biblatex}
        {The entry \thefield{entrykey} has no URL.\MessageBreak
         No link will be created}%
      \printfield{postnote}}
     {\href{\thefield{url}}
        {\iffieldundef{postnote}
           {\PackageWarning{biblatex}
              {Text argument missing,\MessageBreak
               using the title for entry\MessageBreak
               \thefield{entrykey}}%
            \printfield[citetitle]{labeltitle}}
           {\printfield{postnote}}}}}
  {}
  {}

\newcommand*{\citehrefurlwrap}[2]{\citehrefurl[#2]{#1}}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@online{UseCase20,
  title   = {Use-Case 2.0 ebook},
  author  = {Ivar Jacobson and Ian Spence and Kurt Bittner},
  date    = {2011-12},
  url     = {https://www.ivarjacobson.com/publications/white-papers/use-case-ebook},
  urldate = {2018-12-25},
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
\citehrefurl{UseCase20}

\citehrefurl[some text]{UseCase20}

\citehrefurlwrap{UseCase20}{some other text}

\citeurl{UseCase20}

\href{https://www.ivarjacobson.com/publications/white-papers/use-case-ebook}{sometext}

\printbibliography
\end{document}

_{Sorry there is no image at the moment. I'm having trouble uploading them. Feel free to add a screenshot of the result if you like.}

This is basically a slightly modified version of jakun's \citelink from their answer to How to create a link to a URL provided in a bib file with custom text which was in turn inspired by Create QR-code from citeurl.