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<div class="sect1" lang="en" xml:lang="en">
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<h2 class="title" style="clear: both"><a id="txncursor"></a>Transactional Cursors</h2>
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<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">
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<div>
<h3 class="title"><a id="dplcursors"></a>Using Transactional DPL Cursors</h3>
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<div></div>
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<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>
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