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DBD-XBase-0.160
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/ XBase::FAQ

NAME

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

DESCRIPTION

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

AUTHOR

Jan Pazdziora, adelton@fi.muni.cz

Questions and answers

What Perl version do I need? What other modules?

You need perl at least 5.004. I test each new distribution agains 5.005* and 5.004_04 version of perl. 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.

With XBase.pm, the get_record also returns records marked as deleted. 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 deleted.

However, when reading the same file using 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 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).

I have this dbf/something file created with [your favorite] tool and XBase.pm cannot read it.

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.

I want to install the module but I do not have make on my [your damaged] system.

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. See README.

I have make but I cannot install into default directory and my sysadmin doesn't want to do it for me.

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. 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 differenct 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*, ot 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.

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.

I try to use select * from table where field = '%str%' but it doesn't work. Why?

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 I use XBase.pm/DBD::XBase and it corrupts my dbf's?

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 the module troubles, and I'll try to find a reason and 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 to [fill your] system and I do not know how to install it.

Did you follow the steps in the README? 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 you system is so unstandard that the general instrauction do not help, you should contact your system administrator or the support for your system.

Does the module allow for any aggregate functions in the select, like select max(field) from table?

No, 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.

I try to DBI->connect on my [fill your favorite] system and it 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... 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 shorted, you've got damaged file and XBase.pm/dbfdump only reads as much rows as it can find in the dbf.

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.