DB_File::DB_Database - Perl module for reading and writing the DB_File data as a mutifield table with index file supported.
use DB_File::DB_Database; my $table = new DB_File::DB_Database "dbexample" or die DB_File::DB_Database->errstr;
my @data = $table->get_record("Judy");
my $hashref = $table->get_record_hash('James');
$table->append_record("Caroline", "20", "sister");
$table->append_record_hash('jimmy', "age" => 25,
$table->set_record("Judy", "18", "a beauty");
$table->set_record_hash('Roger', "age" => 25,"msg" => 'everything is easy!');
$table->update_record_hash("Roger", "MSG" => "New message");
$table->delete_record("Roger");
$table->prepare_select( "seek" => {'index'=> 'indexA',
'from' => 10,
'to' => 25},
"where" => {'msg'=> 'hi'},
"top" => 10);
$table->dump_data;
$table->close;
This module can handle DB_File data(DB_HASH, key/value pairs) as a mutifield table.
It also can create auto updated index files(DB_BTREE) to faster the searching speed.
It is an Beta version, use it at your own risk.
The following methods are supported by DB_File::DB_Database module:
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:
readonly open the database file and the index files only for reading
my $table = new DB_File::DB_Database "dbexample" or die DB_File::DB_Database->errstr;
my $table = new DB_File::DB_Database "name" => "dbexample","readonly" => 1;
my $table = new DB_File::DB_Database;
$table->open ("name" => "dbexample","readonly" => 1) or die DB_File::DB_Database->errstr;
my $newtable = DB_File::DB_Database->create( "name" => "dbexample",
"field_names" => [ "Age", "MSG" ],
"field_types" => [ "N", "C" ],
'permits' => 0640 );
The new file mustn't exist yet -- DB_File::DB_Database will not allow you to overwrite existing table. Use drop (or unlink) to delete it first.
More than key/value pairs, DB_File::DB_Database can make key / values(list) pairs.
On success they return true -- the record ID. Index file is automatical updated, if needed.
record(s) by the ID(s). Return a number of how many records is deleted.
Examples of reading and writing:
$table->set_record("Judy", "18", "a beauty");
my @data = $table->get_record("Judy");
my $hashref = $table->get_record_hash('James');
$table->set_record_hash('Roger', "age" => 25,
"msg" => 'everything is easy!');
This is a code to update field MSG in record where record ID is ``Roger''.
use DB_File::DB_Database;
my $table = new DB_File::DB_Database "dbexample" or die DB_File::DB_Database->errstr;
my ($id, $age) = $table->get_record("Roger", "age")
die $table->errstr unless defined $id;
$table->update_record_hash("Roger", "MSG" => "New message");
Basically like above, but do not specify the ID, leave it to DB_File::DB_Database. The ID will be sequent numbers. On success they return true -- the record ID. Index file is automatical updated, if needed.
Examples:
$table->append_record("Caroline", "20", "sister");
$table->append_record_hash('jimmy', "age" => 25,
"msg" => 'Nothing is easy!');
Index file is stored in DB_File BTREE. Once created, all index files will be automatically opened when open the database file, and updated automatically when writing the database file.
'key' => 'Age' # index by the age, from young to old 'key' => '-Age' # index by the age, from old to young 'key' => '-Age(3)+Name' # index by the age(up to 999),then name; from old to young,then from A to Z 'key' => '-Age(3)+-Name' # index by the age(up to 999),then name; from old to young,then from Z to A
'Age(3)' is similar to 'substr(Age,0,3)', only the length of the last field name appeared in the 'key' can be ommited. '+-' CAN'T be subsituded by '-'.
# Index File name will be dbexample_indexA
print $table->create_index( 'name' => 'indexA' ,
'key' => 'Age' , # '-Age' means reverse sort,
'permits'=> 0640 );
# delete Index indexA
print $table->drop_index('indexA');
Select matched records, using index will speed up the searching.
If no ``seek'' specified(do not use index), it will search from the first record to the last(or up to the record numbers you needed).``top'' means select the first ? records. You may use ``cut'' instead, ``cut'' => [2,6] means select from the secord matched record till to the sixth.
for ``seek'', ``from'' is needed, ``to'' can be omitted(till the last).
To fetch the selected record. Use get_record, get_record_nf, get_record_hash, leave the ID undef.
Examples of selecting record:
use DB_File::DB_Database;
my $table = new DB_File::DB_Database "dbexample" or die DB_File::DB_Database->errstr;
my $table = new XBase "names.dbf" or die XBase->errstr;
# find people aged form 10 to 25, select the first 10 people. their 'msg' must content 'hi'
$table->prepare_select( "seek" => {'index'=> 'indexA',
'from' => 10,
'to' => 25},
"where" => {'msg'=> 'hi'},
"top" => 10);
while ( @_ = $table->get_record(undef,'age','msg') ){
### do something here
print ++$i,"\n";
print "@_ ","\n";
}
print the database file records and the index files contenting.
Example of use is
$table->dump_data;
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 DB_File::DB_Database->errstr().
After create_index or recreate_index, file should be closed then open again. or something strange will happed.
if you found any bugs or make any patches, I would be appriciate to hear from you.
Use DB_File(DB_HASH) to store data (key/value pairs). Value use a CSV (comma separated
text) to store a list. No character limits. DB_File::DB_Database do NOT need TEXT::CSV or TEXT::CSV_XS.
but you can easily changed it to that modules.
Index files are stored as DB_File (DB_BTREE). Key is the text, value is the ID.
The locking function is a poor. Every opened file has a '_lock' file(non Windows), No locking is done in Windows.
But to add a locking only need to modify database_lock and database_unlock.
0.031
publish time: 2001.10.22
(c) 2001 冉宁煜 / Ran Ningyu, <rny@yahoo.com.cn> http://perl.yesky.net/ or http://www.skybamboo.com/perl/ at SouthEast University, Nanjing, China.
All rights reserved. This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
DB_File