biblatex reading style - how to remove entries without an annotation?

Question

Here's a MWE that I thought it would only remove entries without the annotation AKA annote field. But actually it removes all of the entries.

Here's what the documentation says, on page 78 of the biblatex manual:

If notfield is used then only apply the step if the ⟨entryfield⟩ does not exist.

If entrynull is set, processing of the \map immediately terminates and the current entry is not created. It is as if it did not exist in the datasource. Obviously, you should select the entries which you want to apply this to using prior mapping steps.

By wrapping these into one step I thought I would first test if the annotation field is set, and then, if not, delete the entry. Is there a way to achieve that.

\documentclass{article}

\usepackage[style=reading,
            entryhead=true,
            entrykey=false,
            natbib,
            hyperref=false,
            url=false,
            doi=false,
            %style=apa,
            sorting=nyt,
            isbn=false,
            %backref=true,
            firstinits=true,
            minnames=13,
            maxnames=35,
            minbibnames=10,
            maxbibnames=100,
            parentracker=true,
            defernumbers=true,
            backend=biber]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
     \step[notfield=annotation,entrynull=true]
    }
  }
}

\begin{filecontents}{\jobname.bib}
@inproceedings{ABCDFG,
  annote = {This is a very nice paper.},
  author = {GGPB},
  booktitle = {BOEUS},
  keywords = {clipping},
  title = {NOAP},
  volume = {0},
  year = {2005},
}
@inproceedings{XXXXXX,
  author = {PQR},
  booktitle = {BBC},
  keywords = {LLM},
  title = {ARP},
  year = {2010},
}
\end{filecontents}

\addbibresource{\jobname.bib}

\begin{document}

\nocite{*}

\printbibliography

\end{document}

Answer 1

Data mapping happens at a very early state when the annote field is still called annote and not yet annotation (the renaming from annote to annotation also happens in a sourcemap, but that map is executed after user-defined \DeclareSourcemaps). So you need notfield=annote.

Furthermore, it seems that entrynull only works safely if it is used in a \step of its own. All examples in the documentation use it like this.

If you think that \step[notfield=annotation,entrynull=true] should work (and from the text of the documentation I found no compelling argument that it should not), please open an issue at the Biber bugtracker: https://github.com/plk/biber/issues.

edit: There was a discussion about this on the Biber bugracker at https://github.com/plk/biber/issues/238. As a consequence the biblatex documentation has been amended to emphasise that notfield should be used in a \step of its own together with final.

To catch entries without annote and annotation and null them I suggest

\documentclass{article}
\usepackage[style=reading, backend=biber]{biblatex}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
     \step[notfield=annote, final]
     \step[notfield=annotation, final]
     \step[entrynull]
    }
  }
}

\begin{filecontents}{\jobname.bib}
@inproceedings{ABCDFG,
  annote    = {This is a very nice paper.},
  author    = {GGPB},
  booktitle = {BOEUS},
  keywords  = {clipping},
  title     = {NOAP},
  volume    = {0},
  year      = {2005},
}
@inproceedings{XXXXXX,
  author    = {PQR},
  booktitle = {BBC},
  keywords  = {LLM},
  title     = {ARP},
  year      = {2010},
}
\end{filecontents}

\addbibresource{\jobname.bib}

\begin{document}
\nocite{*}
\printbibliography
\end{document}