NAME¶
XBase - Perl module for reading and writing the dbf files
SYNOPSIS¶
use XBase;
my $table = new XBase "dbase.dbf" or die XBase->errstr;
for (0 .. $table->last_record) {
my ($deleted, $id, $msg)
= $table->get_record($_, "ID", "MSG");
print "$id:\t$msg\n" unless $deleted;
}
DESCRIPTION¶
This module can read and write XBase database files, known as dbf in dBase and
FoxPro world. It also reads memo fields from the dbt and fpt files, if needed.
An alpha code of reading index support for ndx, ntx, mdx, idx and cdx is
available for testing -- see the
DBD::Index(3) man page. Module XBase
provides simple native interface to XBase files. For DBI compliant database
access, see the DBD::XBase and DBI modules and their man pages.
The following methods are supported by XBase module:
General methods¶
- new
- Creates the XBase object, loads the info about the table form the dbf
file. The first parameter should be the name of existing dbf file (table,
in fact) to read. A suffix .dbf will be appended if needed. This method
creates and initializes new object, will also check for memo file, if
needed.
The parameters can also be specified in the form of hash: value of
name is then the name of the table, other flags supported are:
memofile specifies non standard name for the associated memo file.
By default it's the name of the dbf file, with extension dbt or fpt.
ignorememo ignore memo file at all. This is useful if you've lost
the dbt file and you do not need it. Default is false.
memosep separator of memo records in the dBase III dbt files. The
standard says it should be "\x1a\x1a". There are however
implamentations that only put in one "\x1a". XBase.pm tries to
guess which is valid for your dbt but if it fails, you can tell it
yourself.
nolongchars prevents XBase to treat the decimal value of character
fields as high byte of the length -- there are some broken products around
producing character fields with decimal values set.
my $table = new XBase "table.dbf" or die XBase->errstr;
my $table = new XBase "name" => "table.dbf",
"ignorememo" => 1;
recompute_lastrecno forces XBase.pm to disbelieve the information
about the number of records in the header of the dbf file and recompute
the number of records. Use this only if you know that some other software
of yours produces incorrect headers.
- close
- Closes the object/file, no arguments.
- create
- Creates new database file on disk and initializes it with 0 records. A dbt
(memo) file will be also created if the table contains some memo fields.
Parameters to create are passed as hash.
You can call this method as method of another XBase object and then you only
need to pass name value of the hash; the structure (fields) of the
new file will be the same as of the original object.
If you call create using class name (XBase), you have to (besides
name) also specify another four values, each being a reference to
list: field_names, field_types, field_lengths and
field_decimals. The field types are specified by one letter strings
(C, N, L, D, ...). If you set some value as undefined, create will make it
into some reasonable default.
my $newtable = $table->create("name" => "copy.dbf");
my $newtable = XBase->create("name" => "copy.dbf",
"field_names" => [ "ID", "MSG" ],
"field_types" => [ "N", "C" ],
"field_lengths" => [ 6, 40 ],
"field_decimals" => [ 0, undef ]);
Other attributes are memofile for non standard memo file location,
codepage to set the codepage flag in the dbf header (it does not
affect how XBase.pm reads or writes the data though, just to make FoxPro
happy), and version to force different version of the dbt (dbt)
file. The default is the version of the object from which you create the
new one, or 3 if you call this as class method (XBase->create).
The new file mustn't exist yet -- XBase will not allow you to overwrite
existing table. Use drop (or unlink) to delete it first.
- drop
- This method closes the table and deletes it on disk (including associated
memo file, if there is any).
- last_record
- Returns number of the last record in the file. The lines deleted but
present in the file are included in this number.
- last_field
- Returns number of the last field in the file, number of fields minus
1.
- field_names, field_types, field_lengths, field_decimals
- Return list of field names and so on for the dbf file.
- field_type, field_length, field_decimal
- For a field name, returns the appropriate value. Returns undef if the
field doesn't exist in the table.
Reading the data one by one¶
When dealing with the records one by one, reading or writing (the following six
methods), you have to specify the number of the record in the file as the
first argument. The range is "0 .. $table->last_record".
- get_record
- Returns a list of data (field values) from the specified record (line of
the table). The first parameter in the call is the number of the record.
If you do not specify any other parameters, all fields are returned in the
same order as they appear in the file. You can also put list of field
names after the record number and then only those will be returned. The
first value of the returned list is always the 1/0 "_DELETED"
value saying whether the record is deleted or not, so on success,
get_record never returns empty list.
- get_record_nf
- Instead if the names of the fields, you can pass list of numbers of the
fields to read.
- get_record_as_hash
- Returns hash (in list context) or reference to hash (in scalar context)
containing field values indexed by field names. The name of the deleted
flag is "_DELETED". The only parameter in the call is the record
number. The field names are returned as uppercase.
Writing the data¶
All three writing methods always undelete the record. On success they return
true -- the record number actually written.
- set_record
- As parameters, takes the number of the record and the list of values of
the fields. It writes the record to the file. Unspecified fields (if you
pass less than you should) are set to undef/empty.
- set_record_hash
- Takes number of the record and hash as parameters, sets the fields,
unspecified are undefed/emptied.
- update_record_hash
- Like set_record_hash but fields that do not have value specified in
the hash retain their value.
To explicitly delete/undelete a record, use methods
delete_record or
undelete_record with record number as a parameter.
Assorted examples of reading and writing:
my @data = $table->get_record(3, "jezek", "krtek");
my $hashref = $table->get_record_as_hash(38);
$table->set_record_hash(8, "jezek" => "jezecek",
"krtek" => 5);
$table->undelete_record(4);
This is a code to update field MSG in record where ID is 123.
use XBase;
my $table = new XBase "test.dbf" or die XBase->errstr;
for (0 .. $table->last_record) {
my ($deleted, $id) = $table->get_record($_, "ID")
die $table->errstr unless defined $deleted;
next if $deleted;
$table->update_record_hash($_, "MSG" => "New message")
if $id == 123;
}
Sequentially reading the file¶
If you plan to sequentially walk through the file, you can create a cursor first
and then repeatedly call
fetch to get next record.
- prepare_select
- As parameters, pass list of field names to return, if no parameters, the
following fetch will return all fields.
- prepare_select_with_index
- The first parameter is the file name of the index file, the rest is as
above. For index types that can hold more index structures in on file, use
arrayref instead of the file name and in that array include file name and
the tag name, and optionaly the index type. The fetch will then
return records in the ascending order, according to the index.
Prepare will return object cursor, the following method are methods of the
cursor, not of the table.
- fetch
- Returns the fields of the next available undeleted record. The list thus
doesn't contain the "_DELETED" flag since you are guaranteed
that the record is not deleted.
- fetch_hashref
- Returns a hash reference of fields for the next non deleted record.
- last_fetched
- Returns the number of the record last fetched.
- find_eq
- This only works with cursor created via prepare_select_with_index.
Will roll to the first record what is equal to specified argument, or to
the first greater if there is none equal. The following fetches
then continue normally.
Examples of using cursors:
my $table = new XBase "names.dbf" or die XBase->errstr;
my $cursor = $table->prepare_select("ID", "NAME", "STREET");
while (my @data = $cursor->fetch) {
### do something here, like print "@data\n";
}
my $table = new XBase "employ.dbf";
my $cur = $table->prepare_select_with_index("empid.ndx");
## my $cur = $table->prepare_select_with_index(
["empid.cdx", "ADDRES", "char"], "id", "address");
$cur->find_eq(1097);
while (my $hashref = $cur->fetch_hashref
and $hashref->{"ID"} == 1097) {
### do something here with $hashref
}
The second example shows that after you have done
find_eq, the
fetches continue untill the end of the index, so you have to check
whether you are still on records with given value. And if there is no record
with value 1097 in the indexed field, you will just get the next record in the
order.
The updating example can be rewritten to:
use XBase;
my $table = new XBase "test.dbf" or die XBase->errstr;
my $cursor = $table->prepare_select("ID")
while (my ($id) = $cursor->fetch) {
$table->update_record_hash($cursor->last_fetched,
"MSG" => "New message") if $id == 123
}
Dumping the content of the file¶
A method
get_all_records returns reference to an array containing array
of values for each undeleted record at once. As parameters, pass list of
fields to return for each record.
To print the content of the file in a readable form, use method
dump_records. It prints all not deleted records from the file. By
default, all fields are printed, separated by colons, one record on a row. The
method can have parameters in a form of a hash with the following keys:
- rs
- Record separator, string, newline by default.
- fs
- Field separator, string, one colon by default.
- fields
- Reference to a list of names of the fields to print. By default it's
undef, meaning all fields.
- undef
- What to print for undefined (NULL) values, empty string by default.
Example of use is
use XBase;
my $table = new XBase "table" or die XBase->errstr;
$table->dump_records("fs" => " | ", "rs" => " <-+\n",
"fields" => [ "id", "msg" ]);'
Also note that there is a script
dbf_dump(1) that does the printing.
Errors and debugging¶
If the method fails (returns false or null list), the error message can be
retrieved via
errstr method. If the
new or
create method
fails, you have no object so you get the error message using class syntax
"XBase->errstr()".
The method
header_info returns (not prints) string with information about
the file and about the fields.
Module
XBase::Base(3) defines some basic functions that are inherited by
both XBase and
XBase::Memo(3) module.
DATA TYPES¶
The character fields are returned "as is". No charset or other
translation is done. The numbers are converted to Perl numbers. The date
fields are returned as 8 character string of the 'YYYYMMDD' form and when
inserting the date, you again have to provide it in this form. No checking for
the validity of the date is done. The datetime field is returned in the number
of (possibly negative) seconds since 1970/1/1, possibly with decimal part
(since it allows precision up to 1/1000 s). To get the fields, use the gmtime
(or similar) Perl function.
If there is a memo field in the dbf file, the module tries to open file with the
same name but extension dbt, fpt or smt. It uses module
XBase::Memo(3)
for this. It reads and writes this memo field transparently (you do not know
about it) and returns the data as single scalar.
INDEX, LOCKS¶
New: A support for ndx, ntx, mdx, idx and cdx index formats is available
with alpha status for testing. Some of the formats are already rather stable
(ndx). Please read the
XBase::Index(3) man page and the eg/use_index
file in the distribution for examples and ideas. Send me examples of your data
files and suggestions for interface if you need indexes.
General locking methods are
locksh,
lockex and
unlock for
shared lock, exclusive lock and unlock. They call flock but you can redefine
then in XBase::Base package.
This module is built using information from and article XBase File Format
Description by Erik Bachmann, URL
http://www.clicketyclick.dk/databases/xbase/format/
Thanks a lot.
VERSION¶
1.02
AVAILABLE FROM¶
http://www.adelton.com/perl/DBD-XBase/
AUTHOR¶
(c) 1997--2011 Jan Pazdziora.
All rights reserved. This package is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
Contact the author at jpx dash perl at adelton dot com.
THANKS¶
Many people have provided information, test files, test results and patches.
This project would not be so great without them. See the Changes file for (I
hope) complete list. Thank you all, guys!
Special thanks go to Erik Bachmann for his great page about the file structures;
to Frans van Loon, William McKee, Randy Kobes and Dan Albertsson for longtime
cooperation and many emails we've exchanged when fixing and polishing the
modules' behaviour; and to Dan Albertsson for providing support for the
project.
SEE ALSO¶
perl(1); XBase::
FAQ(3); DBD::
XBase(3) and
DBI(3) for
DBI interface;
dbf_dump(1)