For my thesis I have to write a literature review. Within the review I must use "shorthand" names for cited works like "S001" and "S002" for the first and the second work that will be cited.

In later chapters the Author(year) style has to be used. Unfortunately the two styles will be mixed-up. I did not find a proper solution, anyone that can help?

    begin{filecontents}{myfilea.bib}

@book{goossens93,

    author    = "Michel Goossens and Frank Mittelbach and Alexander Samarin",

    title     = "The LaTeX Companion",

    year      = "1993",

%    shorthand = "GMS"

}



@book{else2015,

    author    = "Someone Else",

    title     = "Interesting thing.",

    year      = "2015",

    shorthand = "ElseShort",

}



@article{borges2018,

    author = {Borges, M.  and Barros, E.  and Maia, P. H.},

    title = {Cloud restriction solver: A refactoring-based approach to migrate applications to the cloud},

    journal = {Information and Software Technology},

    uuid = {52D09357-6BA8-4CB1-91B8-8C4CDD7E351B},

    volume = {95},

    pages = {346-365},

    shorthand = {S002},

    year = {2018},

}

end{filecontents}



documentclass{article}



    usepackage[automark, draft=false]{scrlayer-scrpage}

    setcounter{secnumdepth}{3}

    setcounter{tocdepth}{3}

    usepackage[utf8]{inputenc}

    usepackage[T1]{fontenc}

    usepackage{lmodern}

    usepackage{mathptmx}

    usepackage{courier}

    usepackage[protrusion,factor=900]{microtype}

    usepackage{setspace}

    usepackage{printlen}





usepackage[backend=biber, %% Hilfsprogramm "biber" (statt "biblatex" oder "bibtex")

                style=authoryear, %% Zitierstil: Authorennamen lang [Jahr]

            bibencoding=utf8,

                natbib=true, %% Bereitstellen von natbib-kompatiblen Zitierkommandos

                backref=true, %% Seiten anzeigen, auf denen die Referenz vorkommt

                ibidtracker=context, %% EBENDA-Anzeige bei mehrfachen Zitierungen der selben Quelle auf einer Seite 

                block=space, %% kleiner horizontaler Platz zwischen den Feldern

                isbn=false, %% ISBN nicht anzeigen, gleiches geht mit nahezu allen anderen Feldern

                url=false, %% Url-Feld wird ausgeblendet. Ausnahme: Online-Typ

                pagetracker=true, %% ebd. bei wiederholten Angaben (false=ausgeschaltet, page=Seite, spread=Doppelseite, true=automatisch)

                citetracker=true, % Wird benötigt für kapitelweise Referenzen?

                sorting=nyt, % To get an sorted bibliography

                ]{biblatex}



% "notoccite" prevents cites in captions from misnumbering of references

usepackage{notoccite}





% ibidem: Wenn Fußnoten mehrfach auf der selben Seite zur selben Quelle führen, so schreibe "ibidem" (=ebenda).

providecommand*{mkibid}[1]{#1}

DeclareCiteCommand{footpartcite}[mkbibfootnote]

  {usebibmacro{prenote}}

  {usebibmacro{citeindex}%

   ifthenelse{ifciteibidANDNOTiffirstonpage}

     {printtext[bibhyperref]{bibstring[mkibid]{ibidem}}}

     {printtext[brackets]{usebibmacro{cite}}%

      setunit{addnbspace}%

      printnames{labelname}%

      setunit{labelnamepunct}%

      printfield[citetitle]{title}%

      newunit

      printfield{year}}}

  {multicitedelim}

  {usebibmacro{postnote}}





%usepackage[backend=biber,citestyle=authoryear]{biblatex}

addbibresource{myfilea.bib}



begin{document}



In my case I want to use the author (year) citation style: citet{goossens93}.



But something went wrong: When I use shorthand within a bib element, shorthand and the authoryear will be mixed up: citet{else2015} 



This is only the "shorthand"-style which I need also within my work: cite{borges2018}. 



And this is the the Author (year) combination -- unfortunately it wrotes the shorthand into the year part!: citet{borges2018}.



end{document}

EDIT:

This is what I want to reach:

I add now a new code example:

begin{filecontents}{myfile.bib}

@book{goossens93,

    author    = "Michel Goossens and Frank Mittelbach and Alexander Samarin",

    title     = "The LaTeX Companion",

    year      = "1993",

%    shorthand = "GMS"

}



@book{else2015,

    author    = "Someone Else",

    title     = "Interesting thing.",

    year      = "2015",

    shorthand = "S003",

}



@article{borges2018,

    author = {Borges, M.  and Barros, E.  and Maia, P. H.},

    title = {Cloud restriction solver: A refactoring-based approach to migrate applications to the cloud},

    journal = {Information and Software Technology},

    uuid = {52D09357-6BA8-4CB1-91B8-8C4CDD7E351B},

    volume = {95},

    pages = {346-365},

    shorthand = {S002},

    year = {2018},

}

end{filecontents}



documentclass{article}



    usepackage[automark, draft=false]{scrlayer-scrpage}

    setcounter{secnumdepth}{3}

    setcounter{tocdepth}{3}

    usepackage[utf8]{inputenc}

    usepackage[T1]{fontenc}

    usepackage{lmodern}

    usepackage{mathptmx}

    usepackage{courier}

    usepackage[protrusion,factor=900]{microtype}

    usepackage{setspace}

    usepackage{printlen}

usepackage{longtable} %needed for longtab

LTchunksize=8 %% Row count for simplify pagebreak for longtabu environment



%% Needed for labelling longtabu!

usepackage{caption}

DeclareCaptionLabelSeparator{tableNewline}{par} 

captionsetup{

  justification=centering,

  labelsep=quad,

  }

captionsetup[longtable]{

  justification=centering,

  labelsep=quad,

  }



usepackage{tabu}

usepackage{hhline} % Needed for longtabu when two hlines (==) should be drawn.



usepackage{tabularx}

usepackage{booktabs} %Professionelle Tabellen



usepackage[backend=biber, %% Hilfsprogramm "biber" (statt "biblatex" oder "bibtex")

                style=authoryear, %% Zitierstil: Authorennamen lang [Jahr]

            bibencoding=utf8,

                natbib=true, %% Bereitstellen von natbib-kompatiblen Zitierkommandos

                backref=true, %% Seiten anzeigen, auf denen die Referenz vorkommt

                ibidtracker=context, %% EBENDA-Anzeige bei mehrfachen Zitierungen der selben Quelle auf einer Seite 

                block=space, %% kleiner horizontaler Platz zwischen den Feldern

                isbn=false, %% ISBN nicht anzeigen, gleiches geht mit nahezu allen anderen Feldern

                url=false, %% Url-Feld wird ausgeblendet. Ausnahme: Online-Typ

                pagetracker=true, %% ebd. bei wiederholten Angaben (false=ausgeschaltet, page=Seite, spread=Doppelseite, true=automatisch)

                citetracker=true, % Wird benötigt für kapitelweise Referenzen?

                sorting=nyt, % To get an sorted bibliography

                ]{biblatex}



usepackage[%

% Standard options

final=true,%

pageanchor=true,%

pagebackref=false,%

hyperindex=true,%

hyperfootnotes=true,%

linktocpage=false,%

breaklinks=false,%

colorlinks=true,%

% PDF options

bookmarks=true,

bookmarksopen=true,%

bookmarksopenlevel=1,%

pdfhighlight=/N,%

allbordercolors={0.85 0.85 1},

citebordercolor={1 1 1},

urlbordercolor={1 1 1},%

% PDF entries

pdftitle={mydoctitle},%

pdfauthor={myname},%

pdfsubject={mysubject},%

pdfcreator={Thomas Salzmann},%

pdfproducer={LaTeX},%

pdfkeywords={mykeywords},%

% PDF misc settings

pdfstartpage=1,% Start PDF Viewer on Page 1

pdfduplex=Simplex,%

pdfpagelabels=true,%

pdfprintscaling=None,%

citecolor=blue,%

filecolor=blue,%

linkcolor=blue,%

urlcolor=black,%

]{hyperref}



% "notoccite" prevents cites in captions from misnumbering of references

usepackage{notoccite}



newcommand{citeNotAsShorthand}[2][blue]{textcolor{#1}{citeauthor{#2} (citeyear{#2}) [citefield{#2}{shorthand}]}}



% ibidem: Wenn Fußnoten mehrfach auf der selben Seite zur selben Quelle führen, so schreibe "ibidem" (=ebenda).

providecommand*{mkibid}[1]{#1}

DeclareCiteCommand{footpartcite}[mkbibfootnote]

  {usebibmacro{prenote}}

  {usebibmacro{citeindex}%

   ifthenelse{ifciteibidANDNOTiffirstonpage}

     {printtext[bibhyperref]{bibstring[mkibid]{ibidem}}}

     {printtext[brackets]{usebibmacro{cite}}%

      setunit{addnbspace}%

      printnames{labelname}%

      setunit{labelnamepunct}%

      printfield[citetitle]{title}%

      newunit

      printfield{year}}}

  {multicitedelim}

  {usebibmacro{postnote}}





%usepackage[backend=biber,citestyle=authoryear]{biblatex}

addbibresource{myfile.bib}



begin{document}



In my case I want to use the author (year) citation style: citet{goossens93}.



But something went wrong: When I use shorthand within a bib element, shorthand and the authoryear will be mixed up: citet{else2015} 



This is only the "shorthand"-style which I need also within my work: cite{borges2018}. 



And this is the the Author (year) combination -- unfortunately it wrotes the shorthand into the year part!: citet{borges2018}.



What I want is this version: citeNotAsShorthand{borges2018}





begin{longtabu} to textwidth {| l | X[1.5,l] %aligned left, twice as wide as second column

                                | X[1,l] |} %aligned left



% Table header on first page of table

    caption{Table of excluded studies during title- and abstract analysis} tabularnewline  

    hline %toprule

    thead{Study}& thead{Title of excluded study (year)} & thead{reason for exclusion} tabularnewline 

    hhline{===}

 %toprule

    endfirsthead



% Table header on every other page of table

    caption{Table of excluded studies during title- and abstract analysis (continued)} tabularnewline          

    hline %toprule

    thead{Study}& thead{Title of excluded study (year)} & thead{reason for exclusion} tabularnewline 

    hhline{===}

    endhead

% End of header



% SCOPUS-search new:

cite{else2015} & citetitle{else2015} (citeyear{else2015}) & Primary focus is not on product management. Focus is on side effects of programs from coding perspective.  tabularnewline 

cite{borges2018} &  citetitle{borges2018} (citeyear{borges2018}) & Grey literature (article in press). tabularnewline 

end{longtabu}



printbiblist[title={List of relevant studies found during literature review},notkeyword=LRexcluded]{shorthand}



printbibliography[segment=3,heading=subbibliography]



end{document}

As mentioned in https://github.com/plk/biblatex/issues/569 textcite/citet is more than just cite with parentheses around the year. You will see different behaviour as well if you use pre- and postnotes, compare cite[cf.][380]{sigfridsson} and textcite[cf.][380]{sigfridsson}.

The idea is that textcite is used as the subject of the sentence for cases like Textcite{sigfridsson} found that .... To make sure that the grammatical structure is the same for all textcites, it will show Authors (shorthand) if the shorthand field is given.

If you want the usual behaviour of cite just with parentheses around the year, I suggest you try biblatex-ext and its cite delimiter feature (§5.3 Delimiters for citation commands of the biblatex-ext documentation).

DeclareInnerCiteDelims{cite}{bibopenparen}{bibcloseparen}

should give you what you want.

Furthermore, I think that study IDs are best dealt with via a dedicated field and not with shorthand. So in the example below I created a new field studyid. If there is an algorithmic way to assign the study ID this could be further automated (this could make for a nice follow-up question), at the moment you have to assign the field value manually in the .bib. studyid is declared a label field so that we can use printbiblist easily.

We define two cite macros citewid and citeonlyid. citewid shows the citation and together with the study ID. citeonlyid shows only the study ID.

Finally we set up everything needed for printbiblist.

documentclass{article}

usepackage[utf8]{inputenc}

usepackage[T1]{fontenc}

usepackage{lmodern}



usepackage{filecontents}

begin{filecontents*}{studyid.dbx}

DeclareDatamodelFields[type=field,datatype=literal,label=true]{studyid}

DeclareDatamodelEntryfields{studyid}

end{filecontents*}



usepackage[backend=biber, style=ext-authoryear, datamodel=studyid]{biblatex}



% cite should give author (year)

DeclareInnerCiteDelims{cite}{bibopenparen}{bibcloseparen}



% define citewid: author (year) [study-id]

RegisterCiteDelims{outer}{citewid}

RegisterCiteDelims{inner}{citewid}

DeclareInnerCiteDelimsAlias{citewid}{cite}

DeclareFieldAlias{extblx@innercitewiddelims}{extblx@innercitedelims}



DeclareFieldFormat{citestudyid}{mkbibbrackets{S#1}}



newbibmacro*{citewid}{%

  usebibmacro{cite}%

  setunit{addspace}%

  printfield[citestudyid]{studyid}}



DeclareCiteCommand{citewid}[mkoutercitewiddelims]

  {usebibmacro{prenote}}

  {usebibmacro{citeindex}%

   usebibmacro{citewid}}

  {multicitedelim}

  {usebibmacro{postnote}}



% define citeonlyid: [study-id]

RegisterCiteDelims{outer}{citeonlyid}

DeclareOuterCiteDelims{citeonlyid}{bibopenbracket}{bibclosebracket}

DeclareCiteCommand{citeonlyid}[mkouterciteonlyiddelims]

  {usebibmacro{prenote}}

  {iffieldundef{studyid}

     {PackageWarning{biblatex}{%

      No 'studyid' in entry 'thefield{entrykey}'.MessageBreak

      Add the 'studyid' fieldMessageBreak

      or don't cite this entry withMessageBreak

      'stringciteonlyid'}}

     {printfield[studyidwidth]{studyid}}}

  {multicitedelim}

  {usebibmacro{postnote}}



% printbiblist similar to shorthand definitions

DeclareBibliographyDriver{studyid}{%

  usedriver

    {}

    {thefield{entrytype}}%

  finentry}



DeclareFieldFormat{studyidwidth}{S#1}

defbibenvironment{studyid}

  {list

     {printfield[studyidwidth]{studyid}}

     {setlength{labelwidth}{studyidwidth}%

      setlength{leftmargin}{labelwidth}%

      setlength{labelsep}{biblabelsep}%

      addtolength{leftmargin}{labelsep}%

      setlength{itemsep}{bibitemsep}%

      setlength{parsep}{bibparsep}%

      renewcommand*{makelabel}[1]{##1hss}}}

  {endlist}

  {item}



DeclareSortingTemplate{studyid}{

  sort{

    field{studyid}

  }

}



begin{filecontents}{jobname.bib}

@article{borges2018,

  author    = {Borges, M.  and Barros, E.  and Maia, P. H.},

  title     = {Cloud restriction solver:

               A refactoring-based approach to migrate applications to the cloud},

  journal   = {Information and Software Technology},

  volume    = {95},

  pages     = {346-365},

  year      = {2018},

  studyid   = {002},

}

@article{licht2009,

  author  = {Licht, Carmilla M. M. and de Geus, Eco J. C.

             and van Dyck, Richard and Penninx, Brenda W. J. H.},

  title   = {Association between anxiety disorders and

             heart rate variability in {The} {Netherlands} {Study} of

             {Depression} and {Anxiety} ({NESDA})},

  journal = {Psychosomatic medicine},

  volume  = {71},

  number  = {5},

  pages   = {508--518},

  doi     = {10.1097/PSY.0b013e3181a292a6},

  date    = {2009},

  studyid = {001},

}

end{filecontents}



addbibresource{jobname.bib}

addbibresource{biblatex-examples.bib}



begin{document}

cite{sigfridsson}



cite{borges2018}



citewid{borges2018}



citeonlyid{borges2018,licht2009}



printbiblist[title=List of studies]{studyid}



printbibliography

end{document}

Thank you for that hint.

I have added now two commands:

newcommand{citeNotAsShorthand}[1]{{citeauthor{#1} (citeyear{#1})}}%



newcommand{citeNotAsShorthanda}[2][blue]{color{#1}{citeauthor{#2} (citeyear{#2}) [citefield{#2}{shorthand}]}}

When I use:
citet{IWSPM2016:Linaker2016} then "Linåker and Wnuk (S030)" will be printed.

When I use
citeNotAsShorthand{IWSPM2016:Linaker2016}
then "Linåker and Wnuk (2016)" will be printed - which is quite good.

And
citeNotAsShorthanda{IWSPM2016:Linaker2016}
prints "Linåker and Wnuk (2016) [S030]".

Great!