<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>Transactional Cursors</title> <link rel="stylesheet" href="gettingStarted.css" type="text/css" /> <meta name="generator" content="DocBook XSL Stylesheets V1.62.4" /> <link rel="home" href="index.html" title="Getting Started with Berkeley DB Transaction Processing" /> <link rel="up" href="usingtxns.html" title="Chapter 3. Transaction Basics" /> <link rel="previous" href="nestedtxn.html" title="Nested Transactions" /> <link rel="next" href="txnindices.html" title="Secondary Indices with Transaction Applications" /> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Transactional Cursors</th> </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td> <th width="60%" align="center">Chapter 3. Transaction Basics</th> <td width="20%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td> </tr> </table> <hr /> </div> <div class="sect1" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2> </div> </div> <div></div> </div> <p> You can transaction-protect your cursor operations by specifying a transaction handle at the time that you create your cursor. Beyond that, you do not ever provide a transaction handle directly to a cursor method. </p> <p> Note that if you transaction-protect a cursor, then you must make sure that the cursor is closed before you either commit or abort the transaction. For example: </p> <pre class="programlisting">#include <stdio.h> #include <stdlib.h> #include "db.h" int main(void) { DBT key, data; DBC *cursorp; DB_TXN *txn = NULL; int ret, c_ret; char *replacementString = "new string"; ... /* environment and db handle creation omitted */ ... /* Get the txn handle */ txn = NULL; ret = envp->txn_begin(envp, NULL, &txn, 0); if (ret != 0) { envp->err(envp, ret, "Transaction begin failed."); goto err; } /* Get the cursor, supply the txn handle at that time */ ret = dbp->cursor(dbp, txn, &cursorp, 0); if (ret != 0) { envp->err(envp, ret, "Cursor open failed."); txn->abort(txn); goto err; } /* * Now use the cursor. Note that we do not supply any txn handles to these * methods. */ /* Prepare the DBTs */ memset(&key, 0, sizeof(DBT)); memset(&data, 0, sizeof(DBT)); while (cursor->get(&key, &data, DB_NEXT) == 0) { data->data = (void *)replacementString; data->size = (strlen(replacementString) + 1) * sizeof(char); c_ret = cursor->put(cursor, &key, &data, DB_CURRENT); if (c_ret != 0) { /* abort the transaction and goto error */ envp->err(envp, ret, "Cursor put failed."); cursorp->close(cursorp); cursorp = NULL; txn->abort(txn); goto err; } } /* * Commit the transaction. Note that the transaction handle * can no longer be used. */ ret = cursorp->close(cursorp); if (ret != 0) { envp->err(envp, ret, "Cursor close failed."); txn->abort(txn); goto err; } ret = txn->commit(txn, 0); if (ret != 0) { envp->err(envp, ret, "Transaction commit failed."); goto err; } err: /* Close the cursor (if the handle is not NULL) * and perform whatever other cleanup is required */ /* Close the database */ /* Close the environment */ ... if (c_ret != 0) ret = c_ret; return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE); } </pre> </div> <div class="navfooter"> <hr /> <table width="100%" summary="Navigation footer"> <tr> <td width="40%" align="left"><a accesskey="p" href="nestedtxn.html">Prev</a> </td> <td width="20%" align="center"> <a accesskey="u" href="usingtxns.html">Up</a> </td> <td width="40%" align="right"> <a accesskey="n" href="txnindices.html">Next</a></td> </tr> <tr> <td width="40%" align="left" valign="top">Nested Transactions </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td width="40%" align="right" valign="top"> Secondary Indices with Transaction Applications</td> </tr> </table> </div> </body> </html>