VIII. 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.
The following handlers are supported:
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 is a newer type and more flexible than dbm. It still has most of the
arbitrary limits of dbm (therefore it is deprecated).
gdbm is the GNU database manager.
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
here. Since it is constant, we support
only reading operations.
Example 1. DBA example 1
2 <?php
3
4 $id = dba_open("/tmp/test.db", "n", "db2");
5
6 if(!$id) {
7 echo "dba_open failed\n";
8 exit;
9 }
10
11 dba_replace("key", "This is an example!", $id);
12
13 if(dba_exists("key", $id)) {
14 echo dba_fetch("key", $id);
15 dba_delete("key", $id);
16 }
17
18 dba_close($id);
19 ?>
20 |
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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 1
2 <?php
3
4 # ...open database...
5
6 $key = dba_firstkey($id);
7
8 while($key != false) {
9 if(...) { # remember the key to perform some action later
10 $handle_later[] = $key;
11 }
12 $key = dba_nextkey($id);
13 }
14
15 for($i = 0; $i < count($handle_later); $i++)
16 dba_delete($handle_later[$i], $id);
17
18 ?>
19 |
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