These functions build the foundation for accessing Berkeley DB
style databases.
This is a general abstraction layer for several file-based databases.
As such, functionality is limited to a common subset of features
supported by modern databases such as
Sleepycat Software's DB2.
(This is not to be confused with IBM's DB2 software, which is
supported through the ODBC functions.)
The behaviour of various aspects depends on the implementation of the
underlying database. Functions such as dba_optimize()
and dba_sync() will do what they promise for one
database and will do nothing for others. You have to download and install
supported dba-Handlers.
Table 1. List of DBA handlers
Handler
Notes
dbm
Dbm is the oldest (original) type of Berkeley DB style
databases. You should avoid it, if possible. We do not support
the compatibility functions built into DB2 and gdbm, because
they are only compatible on the source code level, but cannot
handle the original dbm format.
ndbm
Ndbm is a newer type and more flexible than dbm. It still has
most of the arbitrary limits of dbm (therefore it is
deprecated).
DB2 is Sleepycat Software's
DB2. It is described as "a programmatic toolkit that
provides high-performance built-in database support for both
standalone and client/server applications.
Cdb is "a fast, reliable, lightweight package for creating and
reading constant databases." It is from the author of qmail and
can be found at http://cr.yp.to/cdb.html. Since it is
constant, we support only reading operations. And since PHP 4.3.0
we support writing (not updating) through the internal cdb library.
cdb_make
Since PHP 4.3.0 we support creation (not updating) of cdb files
when the bundled cdb library is used.
flatfile
This is available since PHP 4.3.0 for compatibility with the deprecated
dbm extension only and should be avoided.
However you may use this where files were created in this format. That
happens when configure could not find any external library.
inifile
This is available since PHP 4.3.3 to be able to modify php.ini files
from within PHP scripts. When working with ini files you can pass arrays
of the form array(0=>group,1=>value_name) or strings of the form
"[group]value_name" where group is optional. As the functions
dba_firstkey() and dba_nextkey()
return string representations of the key there is a new function
dba_key_split() available since PHP 5 which allows
to convert the string keys into array keys without loosing FALSE.
When invoking the dba_open() or
dba_popen() functions, one of the
handler names must be supplied as an argument. The actually
available list of handlers is displayed by invoking
phpinfo() or dba_handlers().
By using the --enable-dba=shared
configuration option you can build a dynamic loadable module to enable PHP
for basic support of dbm-style databases. You also have to add support
for at least one of the following handlers by specifying the
--with-XXXX configure switch to your PHP
configure line.
Warning
After configuring and compiling PHP you must execute the following test
from commandline: php run-tests.php ext/dba. This shows
whether your combination of handlers works. Most problematic are
dbm and ndbm which conflict with
many installations. The reason for this is that on several systems these
libraries are part of more than one other library. The configuration test
only prevents you from configuring malfaunctioning single handlers but not
combinations.
Table 2. Supported DBA handlers
Handler
Configure Switch
dbm
To enable support for dbm add
--with-dbm[=DIR].
Note:
dbm normally is a wrapper which often results in failures.
This means you should only use dbm if you are sure it works
and if you really need this format.
ndbm
To enable support for ndbm add
--with-ndbm[=DIR].
Note:
ndbm normally is a wrapper which often results in failures.
This means you should only use ndbm if you are sure it works
and if you really need this format.
gdbm
To enable support for gdbm add
--with-gdbm[=DIR].
db2
To enable support for db2 add
--with-db2[=DIR].
Note:
db2 conflicts with db3 and db4.
db3
To enable support for db3 add
--with-db3[=DIR].
Note:
db3 conflicts with db2 and db4.
db4
To enable support for db4 add
--with-db4[=DIR].
Note:
db4 conflicts with db2 and db3.
Note:
This was added in PHP 4.3.2. In earlier versions of PHP you need to use
--with-db3=DIR with DIR being the
path to db4 library. It is not possible to use db versions starting
from 4.1 with PHP prior to version 4.3.0. Also, the db libraries with
versions 4.1 through 4.1.24 cannot be used in any PHP version.
cdb
To enable support for cdb add
--with-cdb[=DIR].
Note:
Since PHP 4.3.0 you can omit DIR to use the bundled cdb library
that adds the cdb_make handler which allows creation of cdb files
and allows to access cdb files on the network using PHP's streams.
flatfile
To enable support for flatfile add
--with-flatfile.
Note:
This was added in PHP 4.3.0 to add compatibility with deprecated
dbm extension. Use this handler only
when you cannot install one of the libraries required by the other
handlers and when you cannot use bundled cdb handler.
inifile
To enable support for inifile add
--with-inifile.
Note:
This was added in PHP 5.0.0 and allows to read and set microsoft style
.ini files (like the php.ini file).
Note:
Up to PHP 4.3.0 you are able to add both db2 and db3 handler but only one
of them can be used internally. That means that you cannot have both file
formats. Starting with PHP 5.0.0 there is a configuration check avoid such
misconfigurations.
if (dba_exists("key", $id)) { echo dba_fetch("key", $id); dba_delete("key", $id); }
dba_close($id); ?>
DBA is binary safe and does not have any arbitrary limits.
However, it inherits all limits set by the underlying
database implementation.
All file-based databases must provide a way of setting the file
mode of a new created database, if that is possible at all. The
file mode is commonly passed as the fourth argument to
dba_open() or dba_popen().
You can access all entries of a database in a linear way by using the
dba_firstkey() and dba_nextkey()
functions. You may not change the database while traversing it.
Example 2. Traversing a database
<?php
// ...open database...
$key = dba_firstkey($id);
while ($key != false) { if (true) { // remember the key to perform some action later $handle_later[] = $key; } $key = dba_nextkey($id); }
foreach ($handle_later as $val) { dba_delete($val, $id); }
