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 <reference xml:id="ref.dba" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
  <title>Database (dbm-style) Abstraction Layer Functions</title>
  <titleabbrev>dba</titleabbrev>

  <partintro>
   <section xml:id="dba.intro">
    &reftitle.intro;
   <para>
    These functions build the foundation for accessing Berkeley DB
    style databases.
   </para>
   <para>
    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
    <link xlink:href="&url.sleepycat;">Sleepycat Software's DB2</link>.
    (This is not to be confused with IBM's DB2 software, which is
    supported through the <link linkend="ref.uodbc">ODBC functions</link>.)
   </para>
  </section>
   <section xml:id="dba.requirements">
    &reftitle.required;
    <para>
     The behaviour of various aspects depends on the implementation of the
     underlying database. Functions such as <function>dba_optimize</function>
     and <function>dba_sync</function> will do what they promise for one
     database and will do nothing for others. You have to download and install
     supported dba-Handlers.
    <table>
     <title>List of DBA handlers</title>
     <tgroup cols="2">
      <thead>
       <row>
        <entry>Handler</entry>
        <entry>Notes</entry>
       </row>
      </thead>
      <tbody>
       <row>
        <entry><literal>dbm</literal></entry>
        <entry>
         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.
        </entry>
       </row>

       <row>
        <entry><literal>ndbm</literal></entry>
        <entry>
         Ndbm is a newer type and more flexible than dbm. It still has
         most of the arbitrary limits of dbm (therefore it is
         deprecated).
        </entry>
       </row>

       <row>
        <entry><literal>gdbm</literal></entry>
        <entry>
         Gdbm is the <link xlink:href="&url.gdbm;">GNU database
         manager</link>.
        </entry>
       </row>

       <row>
        <entry><literal>db2</literal></entry>
        <entry>
         DB2 is <link xlink:href="&url.sleepycat;">Sleepycat Software's
         DB2</link>. It is described as "a programmatic toolkit that
         provides high-performance built-in database support for both
         standalone and client/server applications.
        </entry>
       </row>

       <row>
        <entry><literal>db3</literal></entry>
        <entry>
         DB3 is <link xlink:href="&url.sleepycat;">Sleepycat Software's
         DB3</link>.
        </entry>
       </row>

       <row>
        <entry><literal>db4</literal></entry>
        <entry>
         DB4 is <link xlink:href="&url.sleepycat;">Sleepycat Software's
         DB4</link>. This is available since PHP 4.3.2.
        </entry>
       </row>

       <row>
        <entry><literal>cdb</literal></entry>
        <entry>
         Cdb is "a fast, reliable, lightweight package for creating and
         reading constant databases." It is from the author of qmail and
         can be found at <link xlink:href="&url.cdb;">&url.cdb;</link>. 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.
        </entry>
       </row>

       <row>
        <entry><literal>cdb_make</literal></entry>
        <entry>
         Since PHP 4.3.0 we support creation (not updating) of cdb files 
         when the bundled cdb library is used.
        </entry>
       </row>

       <row>
        <entry><literal>flatfile</literal></entry>
        <entry>
         This is available since PHP 4.3.0 for compatibility with the deprecated
         <link linkend="ref.dbm">dbm</link> 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.
        </entry>
       </row>

       <row>
        <entry><literal>inifile</literal></entry>
        <entry>
         This is available since PHP 4.3.3 to be able to modify php.ini files 
         from within PHP scripts. When working with ini files you can pass arrays 
         of the form array(0=>group,1=>value_name) or strings of the form 
         "[group]value_name" where group is optional. As the functions 
         <function>dba_firstkey</function> and <function>dba_nextkey</function>
         return string representations of the key there is a new function
         <function>dba_key_split</function> available since PHP 5 which allows
         to convert the string keys into array keys without loosing &false;.
        </entry>
       </row>

       <row>
        <entry><literal>qdbm</literal></entry>
        <entry>
         This is available since PHP 5.0.0. The qdbm library can be loaded from
         <link xlink:href="http://qdbm.sourceforge.net">http://qdbm.sourceforge.net</link>.
        </entry>
       </row>

      </tbody>
     </tgroup>
    </table>
    </para>
    <para>
     When invoking the <function>dba_open</function> or
     <function>dba_popen</function> functions, one of the
     handler names must be supplied as an argument. The actually
     available list of handlers is displayed by invoking
     <function>phpinfo</function> or <function>dba_handlers</function>.
    </para>
   </section>

   &reference.dba.configure;

   <section xml:id="dba.runtime">
    &reftitle.runtime;
    &no.config;
   </section>
   
   <section xml:id="dba.resources">
    &reftitle.resources;
    <para>
    The functions <function>dba_open</function> and
    <function>dba_popen</function> return a handle to the specified
    database file to access which is used by all other dba-function calls.
    </para>
   </section>
   
   <section xml:id="dba.constants">
    &reftitle.constants;
    &no.constants;
   </section>
   
   <section xml:id="dba.examples">
    &reftitle.examples;
     <para>
      <example>
       <title>DBA example</title>
       <programlisting role="php">
<![CDATA[
<?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);
?>
]]>
      </programlisting>
     </example>
    </para>
    <para>
     DBA is binary safe and does not have any arbitrary limits.
     However, it inherits all limits set by the underlying
     database implementation.
    </para>
    <para>
     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
     <function>dba_open</function> or <function>dba_popen</function>.
    </para>
    <para>
     You can access all entries of a database in a linear way by using the
     <function>dba_firstkey</function> and <function>dba_nextkey</function>
     functions. You may not change the database while traversing it.
    </para> 
    <para>
     <example>
      <title>Traversing a database</title>
      <programlisting role="php">
<![CDATA[
<?php

// ...open database...

$key = dba_firstkey($id);

while ($key != false) {
    if (true) {          // remember the key to perform some action later
        $handle_later[] = $key;
    }
    $key = dba_nextkey($id);
}

foreach ($handle_later as $val) {
    dba_delete($val, $id);
}

?>
]]>
      </programlisting>
     </example>
    </para>
   </section>

  </partintro>

&reference.dba.functions;

 </reference>
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