Biblatex replace title with alternate field

Question

Question:

I would like to replace the biblatex+biber title when a .bib entry does not contain a title. For example, if I have the entry:

@article{key123,
  author = {Name AA and Name BB},
  title = {Article title name},
  Year = {2016},
  revjournal = {Journal Name},
}

I want to replace the

Name AA and Name BB. “Article Title Name”. In: (2016).

with

Name AA and Name BB. “Article Title Name”. Under review at: Journal Name (2016).

What I have tried:

I have attempted to map revjournal to usera with the following:

\DeclareSourcemap{
    \maps[datatype=bibtex]{
      \map{
        \step[fieldsource=revjournal]
        \step[fieldset=usera,origfieldval]
    }
  }
}

\DeclareFieldFormat{usera}{%
  \iffieldundef{title}{%
    \mkbibacro{Under review at}\addcolon\space#1%
  }{}%
}

But that does nothing. Perhaps there is a better way to replace/overwrite biblatex fields?

MWE:

\documentclass{article}

\usepackage{filecontents}

\usepackage[backend=biber,firstinits=true]{biblatex}
\DeclareSourcemap{
    \maps[datatype=bibtex]{
      \map{
        \step[fieldsource=revjournal]
        \step[fieldset=usera,origfieldval]
    }
  }
}

\DeclareFieldFormat{usera}{%
  \iffieldundef{title}{%
    \mkbibacro{Under review at}\addcolon\space{#1}%
  }{}%
}

\begin{filecontents}{./pubs.bib}
@article{key123,
  author = {Name AA and Name BB},
  title = {Article title name},
  Year = {2016},
  revjournal = {Journal Name},
  }
\end{filecontents}
\bibliography{./pubs.bib}
\begin{document}

\fullcite{key123}
\end{document}

Thank you for your help.

Answer 1

This is an alternative solution to the problem. Biblatex provides the field pubstate to record the publication status of journal articles.

Thus I suggest to keep the standard journaltitle (or the bibtex journal field) and to add the pubstate= {under review} information to the entry.

Thus the bibtex entry looks like

@article{key123,
  author = {Name AA and Name BB},
  title = {Article title name},
  Year = {2016},
  journal = {Journal Name},
  pubstate = {under review},
  }

Then, to process the information and typeset the output in the desired format use:

\def\jmlarson@ur{under review}

\renewbibmacro{in:}{%
  \ifentrytype{article}
    {\iffieldequals{substate}{\jmlarson@ur}{\printtext{Under review at\intitlepunct}}{}\clearfield{pubstate}}
    {\printtext{\bibstring{in}\intitlepunct}}%
}

The trick is to redefine the macro that typeset "In" to put the right text for the appropriate entires, and to clear the information in pubstate (so it is not printed twice).

With the provided MWE, this results in:

Answer 2

A more robust result, courtesy of @moewe is to use:

\iffieldequalstr{pubstate}{under review}

and not declare any macros. For more justification, see here:

Biblatex: iffieldequals appears to return true for false conditions