Library Version 18.1.40

Transactional Cursors
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## Transactional Cursors

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.

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:

    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
    }

### Using Transactional DPL Cursors

When using the DPL, you create the cursor using the entity class's primary or secondary index (see the Getting Started with Berkeley DB for Java guide for details). At the time that you create the cursor, you pass a transaction handle to the `entities()` method, and this causes all subsequent operations performed using that cursor to be performed within the scope of the transaction.

Note that if you are using a transaction-enabled store, then you must provide a transaction handle when you open your cursor.

For example:

    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;
            }
        }

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