How can I tell biblatex to filter entries based on URL and URLDATE?

Question

I would like to create two separate lists of references using biblatex. The first one should contain literature references, the second one online references. My criterion is that any entry with both a Url and a Urldate in the BibTeX file should be an online source. So I defined a “bibcheck” like so:

\documentclass{article}

\usepackage[style=verbose]{biblatex}

\defbibcheck{online}{%
  \ifboolexpr{ 
    not test {\iffieldundef{Url}} and not test {\iffieldundef{Urldate}}
  }{% Entry has both url and urldate -> it's a web source  
  }{%
    \skipentry
  }
}

\defbibcheck{hasurl}{%
  \iffieldundef{Url}{\skipentry}{}%
}

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@misc{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
  url = {http://www.google.com/},
  urldate = {2012-06-21}
}
@misc{B02,
  author = {Buthor, B.},
  year = {2002},
  title = {Bravo},
  url = {http://www.google.com/}
}
@misc{C03,
  author = {Cuthor, C.},
  year = {2001},
  title = {Charlie},
  urldate = {2012-06-21}
}
@misc{D04,
  author = {Duthor, D.},
  year = {2001},
  title = {Delta}
}
\end{filecontents}

\addbibresource{\jobname.bib}

\nocite{*}

\begin{document}

\printbibliography[check=online]
\printbibliography[check=hasurl]

\end{document}

This does not work, however, because it seems that in the bibcheck “routine” neither Url nor Urldate are set – even though they are printed correctly in the list of references. I tried outputting the value of the Url field using \thefield{url} and it only returns an empty string.

How can I filter based on Url and Urldate?

Answer 1

The problem with your example is that "URLDATE" is not a field. If you check the manual, all the "*DATE" fields are split into their components by the backend and so if you change "urldate" to to "urlyear" then it works.

An alternative is to use the sourcemapping feature with biber:

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \step[fieldsource=url]
      \step[fieldsource=urldate]
      \step[fieldset=keywords, fieldvalue={online}]
    }
  }
}

This will give everything with both URL and URLDATE the keyword "online" which you can then use for bib filtering. Since URLDATE is part of the backend datamodel, you can use it there.

Answer 2

The test on the field urldate, because biblatex uses only the fields defined in the .bblfile. However, why don't you define such entries not as an online type? Then you can test for \ifentrytype (I used biber in my example):

\documentclass{article}

\usepackage[style=verbose,backend=biber]{biblatex}

\defbibcheck{online}{\ifentrytype{online}{}{\skipentry}}
\defbibcheck{hasurl}{\iffieldundef{url}{\skipentry}{}}
\defbibcheck{hasurldate}{\iffieldundef{urlyear}{\skipentry}{}}

\usepackage{filecontents}

\begin{filecontents*}{\jobname.bib}
@online{A01,
  author = {Author, A.},
  year = {2001},
  title = {Alpha},
  urldate = {2012-06-21},
  url = {http://www.google.com/},
}
@misc{B02,
  author = {Buthor, B.},
  year = {2002},
  title = {Bravo},
  url = {http://www.google.com/}
}
@misc{C03,
  author = {Cuthor, C.},
  year = {2001},
  title = {Charlie},
  urldate = {2012-06-21},
}
@misc{D04,
  author = {Duthor, D.},
  year = {2001},
  title = {Delta},
}
\end{filecontents*}

\addbibresource{\jobname.bib}
\nocite{*}
\begin{document}

\printbibliography[check=online]
\printbibliography[check=hasurl]
\printbibliography[check=hasurldate]
\printbibliography

\end{document}