libdbd-xbase-perl 1:1.05-1 / usr / share / perl5 / XBase / FAQ.pod

=head1 NAME

XBase::FAQ - Frequently asked questions about the XBase.pm/DBD::XBase
modules

=head1 DESCRIPTION

This is a list of questions people asked since the module has been
announced in fall 1997, and my answers to them.

=head1 AUTHOR

Jan Pazdziora

=head1 Questions and answers

=over 2

=item What Perl version do I need? What other modules?

You need perl 5.10 or newer. You need B<DBI> module version 1.00
or higher, if you want to use the DBD driver (which you should).

=item Can I use B<XBase.pm> under Windows 95/NT?

Yes. It's a standard Perl module so there is no reason it shouldn't.
Or, actually, there are a lot of reasons why standard thing do not
work on systems that are broken, but I'm trying hard to workaround
these bugs. If you find a problem on these platform, send me
a description and I'll try to find yet another workaround.

=item Is there a choice of the format of the date?

The only possible format in which you can get the date and that the
module expect for inserts and updates is a 8 char string 'YYYYMMDD'.
It is not possible to change this format. I prefer to do the formating
myself since you have more control over it.

=item The C<get_record> also returns deleted records. Why?

Because. You get the _DELETED flag as the first value of the array.
This gives you a possibility to decide what to do -- undelete,
ignore... It's a feature -- you say you want a record of given
number, you get it and get additional information, if the record is or
isn't marked deleted.

=item But with B<DBD::XBase>, I do not see the deleted records.

That's correct: B<DBD::XBase> only gives you records that are positively
in the file and not deleted. Which shows that B<XBase.pm> is a lower
level tool because you can touch records that are marked deleted, while
B<DBD::XBase> is higher level -- it gives you SQL interface and let's you
work with the file more naturaly (what is deleted should stay
deleted).

=item B<XBase.pm> cannot read files created with [your favorite tool].

Describe exactly, what you expect and what you get. Send me the file
(I understand attachments, uuencode, tar, gzip and zip) so that
I can check what it going on and make B<XBase.pm> undestand your file.
A small sample (three rows, or so) are generally enough but you can
send the whole file if it doesn't have megabytes. Please understand

=item How to install the module when I do not have B<make>?

On Win* platform and with ActiveState port, use ppm to install
B<DBD::XBase> from ActiveState's site. You can also just copy the files
from the lib directory of the distribution to where perl can find
them. Also check whether your make doesn't hide under different names
(nmake, gmake). See C<README>.

=item I have make but I cannot install into default directory.

Ask your sysadmin to do it for your. If he refuses, fire the
sysadmin. See C<README> for how to install into and use nonstandard
place for the module.

=item Can I access one dbf file both from Perl and (say) Clipper?

For reading -- yes. For writing -- B<XBase.pm> has a locksh and lockex
method to lock the file. The question is to what extend Clipper (or
Fox* or whatever) uses the same system calls, documentation of native
XBase applications doesn't tell this. So the answer is that for
multiple updates you should probably consider real RDBMS system
(PostgreSQL, MySQL, Oracle, to name a few).

=item B<XBase.pm/DBD::XBase> breaks my accented characters.

No, it doesn't. The character data is returned exactly as it appears
in the dbf/dbt file. You probably brought the file from different
system that uses differend character encodings. So some bytes in the
strings have different meaning on that system. You also probably have
fonts in different encoding on that system. In the Czech language, we
have about 6 different encoding that affect possition at which
accented characters appear.

So what you really want to do is to use some external utility to
convert the strings to encoding you need -- for example, when I bring
the dbf from Win*, it often is in the Windows-1250 or PC-Latin-2
encoding, while the standard is ISO-8859-2. I use my utility
B<Cz::Cstocs> to do the conversion, you maight also try GNU program
B<recode> or use B<Text::Iconv> Perl module.

=item How do I access the fields in the memo file?

Just read the memo field, it will fetch the data from the memo file
for you transparently.

=item Matching with C<field = '%str%'> doesn't work.

If you want to match wildcards with B<DBD::XBase>, you have to use C<like>:

	select * from table where field like '%str%'

=item Can I sue you if B<XBase.pm/DBD::XBase> corrupts my data?

No. At least, I hope no. The software is provided without any
warranty, in a hope you might find is useful. Which is by the way
the same as with most other software, even if you pay for that. What
is different with B<XBase.pm/DBD::XBase> is the fact that if you find out
that the results are different from those expected, you are welcome to
contact me, describe the problem and send me the files that give troubles
to the module, and I'll try to find fix the module.

=item What dbf/other files standard does the module support?

I try to support any file that looks reasonably as
dbf/dbt/fpt/smt/ndx/ntx/mdx/idx/cdx. There are many clones of
XBase-like software, each adding its own extension. The module tries
to accept all different variations. To do that, I need your
cooperation however -- usually good description of the problem, file
sample and expected results lead to rather fast patch.

=item What SQL standard does the B<DBD::XBase> support?

If supports a reasonable subset of the SQL syntax, IMHO. So you can do
select, delete, insert and update, create and drop table. If there is
something that should be added, let me know and I will consider it.
Having said that, I do not expect to ever support joins, for example.
This module is more a parser to read files from your legacy
applications that a RDBMS -- you can find plenty of them around -- use
them.

=item I downloaded you module I do not know how to install it.

Did you follow the steps in the C<README> and C<INSTALL> files? Where
did it fail? This module uses a standard way modules in Perl are
installed. If you've never installed a module on your system and your
system is so non-standard that the general instruction do not help,
you should contact your system administrator or the support for your
system.

=item C<select max(field) from table> does not work.

Aggregate functions are not supported. It would probably be very
slow, since the DBD doesn't make use of indexes at the moment. I do
not have plans to add this support in some near future.

=item C<DBI-E<gt>connect> says that the directory doesn't exist ...

... but it's there. Is B<DBD::XBase> mad or what?

The third part of the first parameter to the connect is the directory
where B<DBD::XBase> will look for the dbf files. During connect, the
module checks C<if -d $directory>. So if it says it's not there, it's not
there and the only thing B<DBD::XBase> can do about it is to report it to
you. It might be that the directory is not mounted, you do not have
permissions to it, the script is running under different UID than when
you try it from command line, or you use relative patch and run the
script from a different directory (pwd) than you expect. Anyway, add

	die "Error reading $dir: $!\n" unless -d $dir;

to your script and you will see that it's not B<DBD::XBase> problem.

=item The B<XBase.pm/dbf_dump> stops after reading I<n> records ...

... why doesn't it read all I<10 x n> records?

Check if the file isn't truncated. C<dbf_dump -i file.dbf> will tell
you the expected number of records and length of one record, like

	Filename:       file.dbf
	Version:        0x03 (ver. 3)
	Num of records: 65
	Header length:  1313
	Record length:  1117
	Last change:    1998/12/18
	Num fields:     40

So the expected length of the file is at least I<1313 + 65 * 1117>. If
it's shorter, you've got damaged file and B<XBase.pm/dbf_dump> only
reads as much rows as it can find in the dbf.

=item How is this B<DBD::XBase> related to B<DBD::ODBC>?

B<DBD::XBase> reads the dbf files directly, using the (included)
B<XBase.pm> module. So it will run on any platform with reasonable new
perl. With B<DBD::ODBC>, you need an ODBC server, or some program, that
B<DBD::ODBC> could talk to. Many proprietary software can serve as ODBC
source for dbf files, it just doesn't seem to run on Un*x systems. And
is also much more resource intensive, if you just need to read the
file record by record and convert it to HTML page or do similary
simple operation with it.

=item How do I pack the dbf file, after the records were deleted?

B<XBase.pm> doesn't support this directly. You'd probably want to
create new table, copy the data and rename back. Patches are always
welcome.

=item Foxpro doesn't see all fields in dbf created with B<XBase.pm>.

Put 'version' => 3 options in to the create call -- that way we say
that the dbf file is dBaseIII style.

=back

=cut

=head1 AVAILABLE FROM

http://www.adelton.com/perl/DBD-XBase/