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XBase::FAQ(3) |
User Contributed Perl Documentation |
XBase::FAQ(3) |
XBase::FAQ - Frequently asked questions about the XBase.pm/DBD::XBase modules
This is a list of questions people asked since the module has been announced in
fall 1997, and my answers to them.
- What Perl version do I need? What other modules?
- You need perl 5.10 or newer. You need DBI module version 1.00 or
higher, if you want to use the DBD driver (which you should).
- Can I use 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.
- 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.
- The "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.
- But with DBD::XBase, I do not see the deleted records.
- That's correct: DBD::XBase only gives you records that are
positively in the file and not deleted. Which shows that XBase.pm
is a lower level tool because you can touch records that are marked
deleted, while 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).
- 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 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
- How to install the module when I do not have make?
- On Win* platform and with ActiveState port, use ppm to install
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 "README".
- 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
"README" for how to install into and use
nonstandard place for the module.
- Can I access one dbf file both from Perl and (say) Clipper?
- For reading -- yes. For writing -- 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).
- 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
Cz::Cstocs to do the conversion, you maight also try GNU program
recode or use Text::Iconv Perl module.
- 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.
- Matching with "field = '%str%'" doesn't work.
- If you want to match wildcards with DBD::XBase, you have to use
"like":
select * from table where field like '%str%'
- Can I sue you if 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 usefull. Which is by the way the same as with
most other software, even if you pay for that. What is different with
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.
- 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.
- What SQL standard does the 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.
- I downloaded you module I do not know how to install it.
- Did you follow the steps in the "README"
and "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.
- "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.
- "DBI->connect" says that the directory doesn't exist ...
- ... but it's there. Is DBD::XBase mad or what?
The third part of the first parameter to the connect is the
directory where DBD::XBase will look for the dbf files. During
connect, the module checks "if -d
$directory". So if it says it's not there, it's not there
and the only thing 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
DBD::XBase problem.
- The XBase.pm/dbfdump stops after reading n records ...
- ... why doesn't it read all 10 x n records?
Check if the file isn't truncated.
"dbfdump -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 1313 + 65 *
1117. If it's shorter, you've got damaged file and
XBase.pm/dbfdump only reads as much rows as it can find in the
dbf.
- How is this DBD::XBase related to DBD::ODBC?
- DBD::XBase reads the dbf files directly, using the (included)
XBase.pm module. So it will run on any platform with reasonable new
perl. With DBD::ODBC, you need an ODBC server, or some program,
that 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.
- How do I pack the dbf file, after the records were deleted?
- 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.
- Foxpro doesn't see all fields in dbf created with XBase.pm.
- Put 'version' => 3 options in to the create call -- that way we say
that the dbf file is dBaseIII style.
http://www.adelton.com/perl/DBD-XBase/
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