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XVII. Database (dbm-style) abstraction layer functions
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
.
(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.
T�bl�zat 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 .
| | db2 |
DB2 is . 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 .
| | 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 . Since it is
constant, we support only reading operations.
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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().
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.
T�bl�zat 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].
| | db3 |
To enable support for db3 add
--with-db3[=DIR].
| | cdb |
To enable support for cdb add
--with-cdb[=DIR].
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Ez a kiterjeszt�s semmilyen konfigur�ci�s
be�ll�t�sokat nem defini�l.
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.
Ez a kiterjeszt�s semmilyen konstans
�rt�ket nem defini�l.
P�lda 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);
?> |
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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.
P�lda 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);
?> |
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User Contributed Notes
Database (dbm-style) abstraction layer functions |
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17-Oct-1999 09:28 |
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With db2, you need to call dba_sync() to get the data written to disk; the
examples are missing this. db2 uses
the BTREE file format, not the more common HASH.
BTREE is faster, though, in my tests, so it's a good
choice.
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17-Jul-2001 12:30 |
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How can I get a list of supported handlers (gdbm,ndb, etc.) in my script?
DBM supports dblist();, but there doesn't seem to be a function to get
this information for dba, or rather it doesn't seem to be publicized,
there should be one out there if phpinfo() can show the information. How
about adding a dbalist();?
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21-May-2002 11:04 |
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Re: how to get a list of handlers. Use
echo phpinfo();
And look for the dba section of the result.
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