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<!--$Id: dbc_get.so,v 10.66 2001/07/12 21:13:02 bostic Exp $-->
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<!--Copyright 1997-2001 by Sleepycat Software, Inc.-->
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<!--All rights reserved.-->
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<title>Berkeley DB: Dbc.get</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<table width="100%"><tr valign=top>
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<a href="../api_java/java_index.html"><img src="../images/api.gif" alt="API"></a><a href="../reftoc.html"><img src="../images/ref.gif" alt="Ref"></a>
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import com.sleepycat.db.*;
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public int get(Dbt key, Dbt data, int flags)
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public int pget(Dbt key, Dbt pkey, Dbt data, int flags)
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<p>The Dbc.get method retrieves key/data pairs from the database. The
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byte array and length of the key
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are returned in the object to which <b>key</b> refers (except for the
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case of the Db.DB_SET flag, in which the <b>key</b> object is
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unchanged), and the byte array
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and length of the data are returned in the object to which <b>data</b>
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<p>When called on a cursor opened on a database that has been made into a
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secondary index using the <a href="../api_java/db_associate.html">Db.associate</a> method, the Dbc.get
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and Dbc.pget methods return the key from the secondary index and the
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data item from the primary database. In addition, the Dbc.pget method
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returns the key from the primary database. In databases that are not
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secondary indices, the Dbc.pget interface will always fail and
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<p>Modifications to the database during a sequential scan will be reflected
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in the scan; that is, records inserted behind a cursor will not be
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returned while records inserted in front of a cursor will be returned.
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<p>In Queue and Recno databases, missing entries (that is, entries that
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were never explicitly created or that were created and then deleted)
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will be skipped during a sequential scan.
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<p>The <b>flags</b> value must be set to one of the following values:
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<p><dt><a name="Db.DB_CURRENT">Db.DB_CURRENT</a><dd>Return the key/data pair to which the cursor refers.
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<p>If the cursor key/data pair was deleted, Dbc.get will return
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<a href="../ref/program/errorret.html#DB_KEYEMPTY">Db.DB_KEYEMPTY</a>.
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<p>If the cursor is not yet initialized, the Dbc.get method throws an exception that encapsulates EINVAL.
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<p><dt><a name="Db.DB_FIRST">Db.DB_FIRST</a>, <a name="Db.DB_LAST">Db.DB_LAST</a><dd>The cursor is set to refer to the first (last) key/data pair of the
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database, and that pair is returned. In the presence of duplicate key
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values, the first (last) data item in the set of duplicates is returned.
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<p>If the database is a Queue or Recno database, Dbc.get using the
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Db.DB_FIRST (Db.DB_LAST) flags will ignore any keys that exist
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but were never explicitly created by the application, or were created and
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<p>If the database is empty, Dbc.get will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_GET_BOTH">Db.DB_GET_BOTH</a><dd>identical to the Db.DB_SET flag, except that both the key and the data
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arguments must be matched by the key and data item in the database.
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<p>When used with the Dbc.pget version of this interface on a secondary
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index handle, both the secondary and primary keys must be matched by the
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secondary and primary key item in the database. It is an error to use the
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Db.DB_GET_BOTH flag with the Dbc.get version of this interface and
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a cursor that has been opened on a secondary index handle.
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<p><dt><a name="Db.DB_GET_RECNO">Db.DB_GET_RECNO</a><dd>Return the record number associated with the cursor. The record number
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will be returned in <b>data</b>, as described in <a href="../api_java/dbt_class.html">Dbt</a>. The
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<b>key</b> parameter is ignored.
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<p>For Db.DB_GET_RECNO to be specified, the underlying database must be
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of type Btree, and it must have been created with the <a href="../api_java/db_set_flags.html#DB_RECNUM">Db.DB_RECNUM</a>
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<p><dt><a name="Db.DB_JOIN_ITEM">Db.DB_JOIN_ITEM</a><dd>Do not use the data value found in all of the cursors as a lookup key for
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the primary database, but simply return it in the key parameter instead.
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The data parameter is left unchanged.
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<p>For Db.DB_JOIN_ITEM to be specified, the underlying cursor must have
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been returned from the <a href="../api_java/db_join.html">Db.join</a> method.
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<p><dt><a name="Db.DB_NEXT">Db.DB_NEXT</a>, <a name="Db.DB_PREV">Db.DB_PREV</a><dd>If the cursor is not yet initialized, Db.DB_NEXT (Db.DB_PREV)
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is identical to Db.DB_FIRST (Db.DB_LAST). Otherwise, the cursor
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is moved to the next (previous) key/data pair of the database, and that
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pair is returned. In the presence of duplicate key values, the value of
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the key may not change.
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<p>If the database is a Queue or Recno database, Dbc.get using the
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Db.DB_NEXT (Db.DB_PREV) flag will skip any keys that exist
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but were never explicitly created by the application, or those that were
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created and later deleted.
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<p>If the cursor is already on the last (first) record in the database,
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Dbc.get will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_NEXT_DUP">Db.DB_NEXT_DUP</a><dd>If the next key/data pair of the database is a duplicate data record for
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the current key/data pair, the cursor is moved to the next key/data pair
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of the database, and that pair is returned. Otherwise, Dbc.get
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will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p>If the cursor is not yet initialized, the Dbc.get method throws an exception that encapsulates EINVAL.
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<p><dt><a name="Db.DB_NEXT_NODUP">Db.DB_NEXT_NODUP</a>, <a name="Db.DB_PREV_NODUP">Db.DB_PREV_NODUP</a><dd>If the cursor is not yet initialized, Db.DB_NEXT_NODUP
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(Db.DB_PREV_NODUP) is identical to Db.DB_FIRST
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(Db.DB_LAST). Otherwise, the cursor is moved to the next (previous)
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non-duplicate key of the database, and that key/data pair is returned.
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<p>If the database is a Queue or Recno database, Dbc.get using the
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Db.DB_NEXT_NODUP (Db.DB_PREV_NODUP) flags will ignore any keys
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that exist but were never explicitly created by the application, or those
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that were created and later deleted.
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<p>If no non-duplicate key/data pairs occur after (before) the cursor
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position in the database, Dbc.get will return <a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_SET">Db.DB_SET</a><dd>Move the cursor to the specified key/data pair of the database, and
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return the datum associated with the given key.
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<p>In the presence of duplicate key values, Dbc.get will return the
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first data item for the given key.
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<p>If the database is a Queue or Recno database, and the specified key exists,
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but was never explicitly created by the application or was later deleted,
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Dbc.get will return <a href="../ref/program/errorret.html#DB_KEYEMPTY">Db.DB_KEYEMPTY</a>.
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<p>If no matching keys are found, Dbc.get will return
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<a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a>.
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<p><dt><a name="Db.DB_SET_RANGE">Db.DB_SET_RANGE</a><dd>The Db.DB_SET_RANGE flag is identical to the Db.DB_SET flag,
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except that the key is returned as well as the data item; and, in the case
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of the Btree access method, the returned key/data pair is the smallest
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key greater than or equal to the specified key (as determined by the
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comparison method), permitting partial key matches and range
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<p><dt><a name="Db.DB_SET_RECNO">Db.DB_SET_RECNO</a><dd>Move the cursor to the specific numbered record of the database, and
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return the associated key/data pair. The <b>data</b> field of the
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must be a byte array containing a record number, as described in
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<a href="../api_java/dbt_class.html">Dbt</a>. This determines the record to be retrieved.
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<p>For Db.DB_SET_RECNO to be specified, the underlying database must be
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of type Btree, and it must have been created with the <a href="../api_java/db_set_flags.html#DB_RECNUM">Db.DB_RECNUM</a>
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<p>In addition, the following flags may be set by
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bitwise inclusively <b>OR</b>'ing them into the <b>flags</b> parameter:
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<p><dt><a name="Db.DB_DIRTY_READ">Db.DB_DIRTY_READ</a><dd>Read modified but not yet committed data. Silently ignored if the
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<a href="../api_java/db_open.html#DB_DIRTY_READ">Db.DB_DIRTY_READ</a> flag was not specified when the underlying
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<p><dt><a name="Db.DB_MULTIPLE">Db.DB_MULTIPLE</a><dd>Return multiple data items. The buffer to which the <b>data</b>
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argument refers is filled with the specified key's data items. If the
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first data item associated with the key cannot fit into the buffer, the
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size field of the <b>data</b> argument is set to the length needed to
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retrieve it, and a <a href="../api_java/mem_class.html">DbMemoryException</a> is thrown. Subsequent calls with both the
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Db.DB_NEXT_DUP and Db.DB_MULTIPLE flags specified will return
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additional data items associated with the current key or
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<a href="../ref/program/errorret.html#DB_NOTFOUND">Db.DB_NOTFOUND</a> if there is no additional data items to return.
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<p>If Db.DB_MULTIPLE is specified for the Queue and Recno access
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methods, the buffer will be filled with as many data records as
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possible. The record number of the first record will be returned in
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the <b>key</b> argument. The record number of each subsequent returned
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record must be calculated from this value.
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<p>The buffer to which the <b>data</b> argument refers should be large
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relative to the page size of the underlying database, aligned for
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unsigned integer access, and be a multiple of 1024 bytes in size.
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<p>The Db.DB_MULTIPLE flag may only be used with the
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Db.DB_CURRENT, Db.DB_FIRST, Db.DB_GET_BOTH,
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Db.DB_NEXT, Db.DB_NEXT_DUP, Db.DB_NEXT_NODUP,
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Db.DB_SET, Db.DB_SET_RANGE, and Db.DB_SET_RECNO
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<p>The Db.DB_MULTIPLE flag may not be used when accessing databases
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made into secondary indices using the <a href="../api_java/db_associate.html">Db.associate</a> method.
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<p>See <a href="../api_java/dbt_bulk_class.html">DbMultipleDataIterator</a> for more information.
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<p><dt><a name="Db.DB_MULTIPLE_KEY">Db.DB_MULTIPLE_KEY</a><dd>Return multiple key and data pairs. The buffer to which the
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<b>data</b> argument refers is filled with key and data pairs. If the
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first key and data pair cannot fit into the buffer, the size field of
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the <b>data</b> argument is set to the length needed to retrieve them,
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and a <a href="../api_java/mem_class.html">DbMemoryException</a> is thrown.
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<p>The buffer to which the <b>data</b> argument refers should be large
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relative to the page size of the underlying database, aligned for
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unsigned integer access, and be a multiple of 1024 bytes in size.
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<p>The Db.DB_MULTIPLE_KEY flag may only be used with the
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Db.DB_CURRENT, Db.DB_FIRST, Db.DB_GET_BOTH,
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Db.DB_NEXT, Db.DB_NEXT_NODUP, Db.DB_SET,
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Db.DB_SET_RANGE, and Db.DB_SET_RECNO options. The
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Db.DB_MULTIPLE_KEY flag may not be used when accessing databases
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made into secondary indices using the <a href="../api_java/db_associate.html">Db.associate</a> method.
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<p>See <a href="../api_java/dbt_bulk_class.html">DbMultipleKeyDataIterator</a> for more information.
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<p><dt><a name="Db.DB_RMW">Db.DB_RMW</a><dd>Acquire write locks instead of read locks when doing the retrieval.
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Setting this flag can eliminate deadlock during a read-modify-write
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cycle by acquiring the write lock during the read part of the cycle so
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that another thread of control acquiring a read lock for the same item,
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in its own read-modify-write cycle, will not result in deadlock.
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<p>Otherwise, the Dbc.get method throws an exception that encapsulates a non-zero error value on
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<p>If Dbc.get fails for any reason, the state of the cursor will be
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<p>The Dbc.get method may fail and throw an exception encapsulating a non-zero error for the following conditions:
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<p><dt>Db.DB_SECONDARY_BAD<dd>A secondary index references a nonexistent primary key.
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>The specified cursor was not currently initialized.
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<p>The Dbc.pget interface was called with a cursor that does not
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refer to a secondary index.
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<p>If the operation was selected to resolve a deadlock, the
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Dbc.get method will fail and
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throw a <a href="../api_java/deadlock_class.html">DbDeadlockException</a> exception.
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<p>If the requested item could not be returned due to insufficient memory,
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the Dbc.get method will fail and
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throw a <a href="../api_java/mem_class.html">DbMemoryException</a> exception.
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<p>The Dbc.get method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods.
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If a catastrophic error has occurred, the Dbc.get method may fail and throw
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a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>, in which case all subsequent Berkeley DB calls
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will fail in the same way.
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<a href="../api_java/dbc_class.html">Dbc</a>
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<a href="../api_java/dbc_close.html">Dbc.close</a>,
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<a href="../api_java/dbc_count.html">Dbc.count</a>,
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<a href="../api_java/dbc_del.html">Dbc.del</a>,
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<a href="../api_java/dbc_dup.html">Dbc.dup</a>,
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<a href="../api_java/dbc_get.html">Dbc.get</a>,
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<a href="../api_java/dbc_get.html">Dbc.pget</a>,
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<a href="../api_java/dbc_put.html">Dbc.put</a>.
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<p><font size=1><a href="http://www.sleepycat.com">Copyright Sleepycat Software</a></font>
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