XII. 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 subset of features modern databases
such as Sleepycat Software's DB2
support. (This is not to be confused with IBM's DB2 software, which is
supported through the ODBC functions.)
The behaviour of various aspects depend 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.
To add support for any of the following handlers, add the specified --with
configure switch to your PHP configure line:
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. (--with-dbm)
Ndbm is a newer type and more flexible than dbm. It still has
most of the arbitrary limits of dbm (therefore it is
deprecated). (--with-ndbm)
Gdbm is the GNU database
manager. (--with-gdbm)
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." (--with-db2)
DB3 is Sleepycat Software's
DB3. (--with-db3)
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. (--with-cdb)
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);
?>
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DBA is binary safe and does not have any arbitrary limits. 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);
?>
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