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Import BSDDB 4.7.25 (as of svn r89086)

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Zachary Ware
2017-09-04 13:40:25 -05:00
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<?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&lt;String,Inventory&gt; pi =
store.getPrimaryIndex(String.class, Inventory.class);
EntityCursor&lt;Inventory&gt; 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>