<!--$Id: db_associate.so,v 10.36 2003/11/08 19:17:16 bostic Exp $-->
<!--Copyright 1997-2003 by Sleepycat Software, Inc.-->
<!--All rights reserved.-->
<!--See the file LICENSE for redistribution information.-->
<html>
<head>
<title>Berkeley DB: Db::associate</title>
<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
<meta name="keywords" content="embedded,database,programmatic,toolkit,b+tree,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++">
</head>
<body bgcolor=white>
<a name="2"><!--meow--></a>
<table width="100%"><tr valign=top>
<td>
<h3>Db::associate</h3>
</td>
<td align=right>
<a href="../../db42-devel-4.2.52/api_cxx/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a>
<a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a>
</td></tr></table>
<hr size=1 noshade>
<tt>
<h3><pre>
#include <db_cxx.h>
<p>
int
Db::associate(DbTxn *txnid, Db *secondary,
int (*callback)(Db *, const Dbt *, const Dbt *, Dbt *),
u_int32_t flags);
</pre></h3>
<hr size=1 noshade>
<h3>Description: Db::associate</h3>
<p>The Db::associate function is used to declare one database a
secondary index for a primary database. After a secondary database has
been "associated" with a primary database, all updates to the primary
will be automatically reflected in the secondary and all reads from the
secondary will return corresponding data from the primary. Note that
as primary keys must be unique for secondary indices to work, the
primary database must be configured without support for duplicate data
items. See <a href="../../db42-devel-4.2.52/ref/am/second.html">Secondary indices</a> for
more information.</p>
<p>The Db::associate method
either returns a non-zero error value
or throws an exception that encapsulates a non-zero error value on
failure, and returns 0 on success.
</p>
<h3>Parameters</h3>
<p><dl compact>
<p><dt><b>callback</b><dd>
The <b>callback</b> parameter is a callback function that creates a
secondary key from a given primary key and data pair.
<p>The callback parameter may be NULL if both the primary and secondary
database handles were opened with the <a href="../../db42-devel-4.2.52/api_cxx/db_open.html#DB_RDONLY">DB_RDONLY</a> flag.</p>
<p>The callback takes four arguments:</p>
<p><dl compact>
<p><dt><b>secondary</b><dd>The <b>secondary</b> parameter is the database handle for the secondary.
<p><dt><b>key</b><dd>The <b>key</b> parameter is a <a href="../../db42-devel-4.2.52/api_cxx/dbt_class.html">Dbt</a> referencing the primary key.
<p><dt><b>data</b><dd>The <b>data</b> parameter is a <a href="../../db42-devel-4.2.52/api_cxx/dbt_class.html">Dbt</a> referencing the primary data
item.
<p><dt><b>result</b><dd>The <b>result</b> parameter is a zeroed <a href="../../db42-devel-4.2.52/api_cxx/dbt_class.html">Dbt</a> in which the callback
function should fill in <b>data</b> and <b>size</b> fields that describe
the secondary key.
</dl>
<a name="3"><!--meow--></a>
<p>If the callback function needs to allocate memory for the <b>data</b>
field rather than simply pointing into the primary key or datum, the
<b>flags</b> field of the returned <a href="../../db42-devel-4.2.52/api_cxx/dbt_class.html">Dbt</a> should be set to
DB_DBT_APPMALLOC, which indicates that Berkeley DB should free the
memory when it is done with it.</p>
<a name="4"><!--meow--></a>
<p>If any key/data pair in the primary yields a null secondary key and
should be left out of the secondary index, the callback function may
optionally return DB_DONOTINDEX. Otherwise, the callback
function should return 0 in case of success or an error outside of the
Berkeley DB name space in case of failure; the error code will be returned
from the Berkeley DB call that initiated the callback.</p>
<p>If the callback function returns DB_DONOTINDEX for any key/data
pairs in the primary database, the secondary index will not contain any
reference to those key/data pairs, and such operations as cursor
iterations and range queries will reflect only the corresponding subset
of the database. If this is not desirable, the application should
ensure that the callback function is well-defined for all possible
values and never returns DB_DONOTINDEX.</p>
<p><dt><b>flags</b><dd>
The <b>flags</b> parameter must be set to 0 or
the following value:
<p><dl compact>
<p><dt><a name="DB_CREATE">DB_CREATE</a><dd>If the secondary database is empty, walk through the primary and create
an index to it in the empty secondary. This operation is potentially
very expensive.
<p>If the secondary database has been opened in an environment configured
with transactions, each put necessary for its creation will be done in
the context of a transaction created for the purpose.</p>
<p>Care should be taken not to use a newly-populated secondary database in
another thread of control until the Db::associate call has
returned successfully in the first thread.</p>
<p>If transactions are not being used, care should be taken not to modify
a primary database being used to populate a secondary database, in
another thread of control, until the Db::associate call has
returned successfully in the first thread. If transactions are being
used, Berkeley DB will perform appropriate locking and the application need
not do any special operation ordering.</p>
</dl>
In addition, the following flag may be set by
bitwise inclusively <b>OR</b>'ing it into the <b>flags</b> parameter:
<p><dl compact>
<p><dt><a name="DB_AUTO_COMMIT">DB_AUTO_COMMIT</a><dd>Enclose the Db::associate call within a transaction. If the call succeeds,
changes made by the operation will be recoverable. If the call fails,
the operation will have made no changes.
</dl>
<p><dt><b>primary</b><dd>
The associate method called should be a method off a database handle for
the primary database that is to be indexed.
<p><dt><b>secondary</b><dd>
The <b>secondary</b> parameter should be an open database handle of
either a newly created and empty database that is to be used to store
a secondary index, or of a database that was previously associated with
the same primary and contains a secondary index. Note that it is not
safe to associate as a secondary database a handle that is in use by
another thread of control or has open cursors. If the handle was opened
with the <a href="../../db42-devel-4.2.52/api_cxx/env_open.html#DB_THREAD">DB_THREAD</a> flag it is safe to use it in multiple threads
of control after the Db::associate method has returned. Note also
that either secondary keys must be unique or the secondary database must
be configured with support for duplicate data items.
<p><dt><b>txnid</b><dd>
If the operation is to be transaction-protected,
(other than by specifying the DB_AUTO_COMMIT flag),
the <b>txnid</b> parameter is a transaction handle returned from
<a href="../../db42-devel-4.2.52/api_cxx/txn_begin.html">DbEnv::txn_begin</a>; otherwise, NULL.
</dl>
<h3>Errors</h3>
<p>The Db::associate method
may fail and throw
<a href="../../db42-devel-4.2.52/api_cxx/except_class.html">DbException</a>,
encapsulating one of the following non-zero errors, or return one of
the following non-zero errors:</p>
<p><dl compact>
<p><dt>DB_REP_HANDLE_DEAD<dd>The database handle has been invalidated because a replication election
unrolled a committed transaction.
</dl>
<p><dl compact>
<p><dt>EINVAL<dd>If the secondary database handle has already been associated with this or
another database handle; the secondary database handle is not open; the
primary database has been configured to allow duplicates; or if an
invalid flag value or parameter was specified.
</dl>
<hr size=1 noshade>
<h3>Class</h3>
<a href="../../db42-devel-4.2.52/api_cxx/db_class.html">Db</a>
<h3>See Also</h3>
<a href="../../db42-devel-4.2.52/api_cxx/db_list.html">Databases and Related Methods</a>
</tt>
<table width="100%"><tr><td><br></td><td align=right>
<a href="../../db42-devel-4.2.52/api_cxx/api_index.html"><img src="../../db42-4.2.52/images/api.gif" alt="API"></a><a href="../../db42-devel-4.2.52/ref/toc.html"><img src="../../db42-4.2.52/images/ref.gif" alt="Ref"></a>
</td></tr></table>
<p><font size=1><a href="../../db42-devel-4.2.52/sleepycat/legal.html">Copyright (c) 1996-2003</a> <a href="http://www.sleepycat.com">Sleepycat Software, Inc.</a> - All rights reserved.</font>
</body>
</html>
distrib
>
Mandriva
>
2007.0
>
x86_64
>
media
>
main-release
>
by-pkgid
>
a4c98df40e78f6c892308fd6841f950a
>
files
>
205
