<?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">package db.txn; import com.sleepycat.db.Cursor; import com.sleepycat.db.Database; import com.sleepycat.db.DatabaseConfig; import com.sleepycat.db.DatabaseEntry; import com.sleepycat.db.DatabaseException; import com.sleepycat.db.Environment; import com.sleepycat.db.EnvironmentConfig; import com.sleepycat.db.LockMode; import com.sleepycat.db.OperationStatus; import com.sleepycat.db.Transaction; import java.io.File; import java.io.FileNotFoundException; ... Database myDatabase = null; Environment myEnv = null; try { // Database and environment opens omitted String replacementData = "new data"; Transaction txn = myEnv.beginTransaction(null, null); Cursor cursor = null; try { // Use the transaction handle here cursor = db.openCursor(txn, null); DatabaseEntry key, data; DatabaseEntry key, data; while(cursor.getNext(key, data, LockMode.DEFAULT) == OperationStatus.SUCCESS) { data.setData(replacementData.getBytes("UTF-8")); // No transaction handle is used on the cursor read or write // methods. cursor.putCurrent(data); } cursor.close(); cursor = null; txn.commit(); txn = null; } catch (Exception e) { if (cursor != null) { cursor.close(); } if (txn != null) { txn.abort(); txn = null; } } } catch (DatabaseException de) { // Exception handling goes here } </pre> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="dplcursors"></a>Using Transactional DPL Cursors</h3> </div> </div> <div></div> </div> <p> When using the DPL, you create the cursor using the entity class's primary or secondary index (see the <i class="citetitle">Getting Started with Berkeley DB for Java</i> guide for details). At the time that you create the cursor, you pass a transaction handle to the <tt class="methodname">entities()</tt> method, and this causes all subsequent operations performed using that cursor to be performed within the scope of the transaction. </p> <p> Note that if you are using a transaction-enabled store, then you must provide a transaction handle when you open your cursor. </p> <p> For example: </p> <pre class="programlisting">package persist.txn; import com.sleepycat.db.DatabaseException; import com.sleepycat.db.Environment; import com.sleepycat.db.EnvironmentConfig; import com.sleepycat.db.Transaction; import com.sleepycat.persist.EntityCursor; import com.sleepycat.persist.EntityStore; import com.sleepycat.persist.PrimaryIndex; import java.io.File; import java.io.FileNotFoundException; ... Environment myEnv = null; EntityStore store = null; ... // Store and environment open omitted, as is the DataAccessor // instantiation. ... Transaction txn = myEnv.beginTransaction(null, null); PrimaryIndex<String,Inventory> pi = store.getPrimaryIndex(String.class, Inventory.class); EntityCursor<Inventory> pi_cursor = pi.entities(txn, null); try { for (Inventory ii : pi_cursor) { // do something with each object "ii" // A transactional handle is not required for any write operations. // All operations performed using this cursor will be done within // the scope of the transaction, txn. } pi_cursor.close(); pi_cursor = null; txn.commit(); txn = null; // Always make sure the cursor is closed when we are done with it. } catch (Exception e) { if (pi_cursor != null) { pi_cursor.close(); } if (txn != null) { txn.abort(); txn = null; } } </pre> </div> </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>