I am trying to substitute a field (Title) by another custom field (Titlept - title in portuguese) if it exists. Any suggestions?

Question

I've tried to edit a bibmacro copied from standard.bbx. But it does not work. Another solution would be to copy the contents of Titlept into Title, but the Biblatex documentation seem clumsy to me in this respect.

Here is my attempt:

    \renewbibmacro{maintitle+title}{%
     \iffieldundef{titlept}{ % if titlept is undefined
      \iffieldsequal{maintitle}{title}
        {\clearfield{maintitle}%
         \clearfield{mainsubtitle}%
         \clearfield{maintitleaddon}}
        {\iffieldundef{maintitle}
           {}
           {\usebibmacro{maintitle}%
        \newunit\newblock
        \iffieldundef{volume}
          {}
          {\printfield{volume}%
               \printfield{part}%
               \setunit{\addcolon\space}}}}}
               {\printfield{titlept}}%
      \usebibmacro{title}%
      \newunit}

Answer 1

This is easy with biber+biblatex which allows you to re-map the data source as it is read, without changing the source itself. Put this in your biber.conf (see section 3.1.1 of the Biber manual for more details and examples):

<?xml version="1.0" encoding="UTF-8"?>
<config>
  <sourcemap>
    <maps datatype="bibtex" bmap_overwrite="1">
      <map>
        <map_step map_field_source="TITLEPT" map_field_target="TITLE"/>
      </map>
    </maps>
  </sourcemap>
</config>

This will overwrite the TITLE field if it also exists. To only rename the field if the TITLE field does not exist, use bmap_overwrite="0" instead.

Answer 2

The problem here is that you can't use titlept as a custom field name. You have to use the fields that are defined by biblatex. You might use usera for example. Otherwise biblatex is not able to recognize your input fields.

Example:

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

\usepackage{filecontents}

\begin{filecontents}{\jobname.bib}
@book {foo,
    author = {Foo, Francis},
    usera = {My custom title},
    title = {All about Foo},
    year = {2011},
    location = {Footown},
}

@book {bar,
    author = {Bar, Bernie},
    title = {Barstory},
    year = {2000},
    location = {Barcity},
}
\end{filecontents}

\addbibresource{\jobname.bib}

    \renewbibmacro{maintitle+title}{%
     \iffieldundef{usera}{ % if usera is undefined
      \iffieldsequal{maintitle}{title}
        {\clearfield{maintitle}%
         \clearfield{mainsubtitle}%
         \clearfield{maintitleaddon}}
        {\iffieldundef{maintitle}
           {}
           {\usebibmacro{maintitle}%
        \newunit\newblock
        \iffieldundef{volume}
          {}
          {\printfield{volume}%
               \printfield{part}%
               \setunit{\addcolon\space}}}}}
               {\printfield{usera}\newunit\newblock}%
      \usebibmacro{title}%
      \newunit}

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

For more information about custom fields in biblatex you should read section 2.2.4 of the manual.

Currently these custom fields are supported:

• name[a–c] list (name)
  Custom lists for special bibliography styles. Not used by the standard bibliography styles.
• name[a–c]type field (key)
  Similar to authortype and editortype but referring to the fields name[a-c]. Not used by the standard bibliography styles.
• list[a–f] list (literal)
  Custom lists for special bibliography styles. Not used by the standard bibliography styles.
• user[a–f] field (literal)
  Custom lists for special bibliography styles. Not used by the standard bibliography styles.
• verb[a–c] field (literal) Similar to the custom fields above except that these are verbatim fields. Not used by the standard bibliography styles.

Answer 3

I had to renew some macros using the custom fields suggested by Thorsten and it worked like a charm. I ended up in something like the code below. Later on I will publish the complete documented work and I let you know. I had to take user[a] to [d] that substituted Title, Series, Notes and Address fields.

\renewbibmacro{maintitle+title}{%
 \iffieldundef{usera}{ % if the translation is not available...
  \iffieldsequal{maintitle}{title} % it prints the title macro,
    {\clearfield{maintitle}%
     \clearfield{mainsubtitle}%
     \clearfield{maintitleaddon}}
    {\iffieldundef{maintitle}
       {}
       {\usebibmacro{maintitle}%
        \newunit\newblock
        \iffieldundef{volume}
      {}
      {\printfield{volume}%
           \printfield{part}%
           \setunit{\addcolon\space}}}}
           \usebibmacro{title}
           }
           {\printfield{usera}}% Otherwise, it prints the translation.
      \newunit}

and

  \newbibmacro{series+number}{%
   \iffieldundef{userb}{
      \printfield{series}%
      \setunit*{\addspace}%
      \printfield{number}%
  \newunit}
  {\printfield{userb}}}

Many thanks for the help. I hope to give it back to the community.