Introduction
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.)
Requirements
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).
|
| gdbm |
Gdbm is the GNU database
manager.
|
| db2 |
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.
|
| db3 |
DB3 is Sleepycat Software's
DB3.
|
| db4 |
DB4 is Sleepycat Software's
DB4. This is available since PHP 5.0.0.
|
| cdb |
Cdb is "a fast, reliable, lightweight package for creating and
reading constant databases." It is from the author of qmail and
can be found here. 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 bundeled 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.
|
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().
Installation
By using the --enable-dba=shared
configuration option you can build a dynamic loadable modul 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.
Table 2. Supported DBA handlers
| Handler | Configure Switch |
|---|
| dbm |
To enable support for dbm add
--with-dbm[=DIR].
|
| ndbm |
To enable support for ndbm add
--with-ndbm[=DIR].
|
| 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 5.0.0. In earlier version you need to use
--with-db3=DIR with DIR being the
path to db4 librarie. It is not possible to use db versions starting
from 4.1 with PHP prior to version 4.3.0.
|
| cdb |
To enable support for cdb add
--with-cdb[=DIR].
Note:
Since PHP 4.3.0 you can omit DIR to use the bundeled 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. Uee this handler only
when you cannot install one of the libraries required by the other
handlers and when you cannot use bundeled cdb handler.
|
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
missconfigurations.
Runtime Configuration
This extension has no configuration directives defined in php.ini.
Resource Types
The functions dba_open() and
dba_popen() return a handle to the specified
database file to access which is used by all other dba-function calls.
Predefined Constants
This extension has no constants defined.
Examples
Example 1. DBA example <?php
$id = dba_open ("/tmp/test.db", "n", "db2");
if (!$id) {
echo "dba_open failed\n";
exit;
}
dba_replace ("key", "This is an example!", $id);
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 (...) { // remember the key to perform some action later
$handle_later[] = $key;
}
$key = dba_nextkey ($id);
}
for ($i = 0; $i < count($handle_later); $i++)
dba_delete ($handle_later[$i], $id);
?> |
|
