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 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.
When invoking the dba_open() or dba_popen() functions, one of the following handler names must
be supplied as an argument. The actually available list of handlers is displayed by invoking phpinfo(). (To add support for any of the following
handlers during the production of PHP, add the specified --with-XXXX configure switch to
your PHP configure line.)
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. (--with-dbm) |
| 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). (--with-ndbm) |
| gdbm |
Gdbm is the GNU database manager. (--with-gdbm) |
| 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."
(--with-db2) |
| db3 |
DB3 is
Sleepycat Software's DB3. (--with-db3) |
| 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. (--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);
?>
|
|
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);
?>
|
|
- Table of Contents
- dba_close -- Close database
- dba_delete -- Delete entry specified by
key
- dba_exists -- Check whether key exists
- dba_fetch -- Fetch data specified by key
- dba_firstkey -- Fetch first key
- dba_insert -- Insert entry
- dba_nextkey -- Fetch next key
- dba_popen -- Open database persistently
- dba_open -- Open database
- dba_optimize -- Optimize database
- dba_replace -- Replace or insert entry
- dba_sync -- Synchronize database
|
