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int com::sleepycat::db::Db::get ( DbTxn  txnid,
Dbt  key,
Dbt  data,
int  flags 
) throws DbException [inline]

The Db.get method retrieves key/data pairs from the database. The byte array and length of the data associated with the specified key are returned in the structure to which data refers.

In the presence of duplicate key values, Db.get will return the first data item for the designated key. Duplicates are sorted by insert order, except where this order has been overridden by cursor operations. Retrieval of duplicates requires the use of cursor operations. See Dbc.get for details.

When called on a database that has been made into a secondary index using the Db.associate method, the Db.get method returns the key from the secondary index and the data item from the primary database. In addition, the second method signature returns the key from the primary database. In databases that are not secondary indices, the second method signature will always fail.

Parameters:
data The data Dbt operated on.
flags must be set to 0 or one of the following values:
  • Db.DB_CONSUME

    Return the record number and data from the available record closest to the head of the queue, and delete the record. The cursor will be positioned on the deleted record. The record number will be returned in key , as described in Dbt. The data will be returned in the data parameter. A record is available if it is not deleted and is not currently locked. The underlying database must be of type Queue for Db.DB_CONSUME to be specified.

  • Db.DB_GET_BOTH

    Retrieve the key/data pair only if both the key and data match the arguments.

    When used with the second method signature version of this method on a secondary index handle, return the secondary key/primary key/data tuple only if both the primary and secondary keys match the arguments. It is an error to use the Db.DB_GET_BOTH flag with the first method signature version of this method and a secondary index handle.

  • Db.DB_SET_RECNO

    Retrieve the specified numbered key/data pair from a database. Upon return, both the key and data items will have been filled in.

    The data field of the specified key must be a byte array large enough to hold a logical record number (that is, an int). This record number determines the record to be retrieved.

    For Db.DB_SET_RECNO to be specified, the underlying database must be of type Btree, and it must have been created with the DB_RECNUM flag.

In addition, the following flags may be set by bitwise inclusively OR 'ing them into the flags parameter:
  • Db.DB_AUTO_COMMIT

    Enclose the Db.get call within a transaction. If the call succeeds, changes made by the operation will be recoverable. If the call fails, the operation will have made no changes. This flag may only be specified with the Db.DB_CONSUME and Db.DB_CONSUME_WAIT flags.

  • Db.DB_DIRTY_READ

    Read modified but not yet committed data. Silently ignored if the Db.DB_DIRTY_READ flag was not specified when the underlying database was opened.

  • Db.DB_MULTIPLE

    Return multiple data items in the buffer to which the data parameter refers.

    In the case of Btree or Hash databases, all of the data items associated with the specified key are entered into the buffer. In the case of Queue or Recno databases, all of the data items in the database, starting at, and subsequent to, the specified key, are entered into the buffer.

    The buffer to which the data parameter refers must be provided from user memory (see Db.DB_DBT_USERMEM ). The buffer must be at least as large as the page size of the underlying database, aligned for unsigned integer access, and be a multiple of 1024 bytes in size. If the buffer size is insufficient, then upon return from the call the size field of the data parameter will have been set to an estimated buffer size, and a DbMemoryException is thrown. (The size is an estimate as the exact size needed may not be known until all entries are read. It is best to initially provide a relatively large buffer, but applications should be prepared to resize the buffer as necessary and repeatedly call the method.)

    The Db.DB_MULTIPLE flag may only be used alone, or with the Db.DB_GET_BOTH and Db.DB_SET_RECNO options. The Db.DB_MULTIPLE flag may not be used when accessing databases made into secondary indices using the Db.associate method.

    See DbMultipleDataIterator for more information.

  • Db.DB_RMW

    Acquire write locks instead of read locks when doing the retrieval. Setting this flag can eliminate deadlock during a read-modify-write cycle by acquiring the write lock during the read part of the cycle so that another thread of control acquiring a read lock for the same item, in its own read-modify-write cycle, will not result in deadlock.

    Because the Db.get method will not hold locks across Berkeley DB calls in non-transactional operations, the Db.DB_RMW flag to the Db.get call is meaningful only in the presence of transactions.

Parameters:
key The key Dbt operated on.
pkey the return key from the primary database.
txnid If the operation is to be transaction-protected, the txnid parameter is a transaction handle returned from DbEnv.txnBegin; otherwise, null.
Exceptions:
DbException The Db.get method may fail and throw DbException, encapsulating one of the following non-zero errors:
DbDeadlockException If a transactional database environment operation was selected to resolve a deadlock, the Db.get method will fail and throw a DbDeadlockException exception.
DbLockNotGrantedException If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time, the Db.get method will fail and throw a DbLockNotGrantedException exception.
DbLockNotGrantedException If the Db.DB_CONSUME_WAIT flag was specified, lock or transaction timers were configured and the lock could not be granted before the wait-time expired, the Db.get method will fail and throw a DbLockNotGrantedException exception.
IllegalArgumentException The Db.get method will fail and throw a IllegalArgumentException exception if a record number of 0 was specified; the Db.DB_THREAD flag was specified to the Db.open method and none of the Db.DB_DBT_MALLOC, Db.DB_DBT_REALLOC or Db.DB_DBT_USERMEM flags were set in the Dbt; the second method signature was called with a Db handle that does not refer to a secondary index; or if an invalid flag value or parameter was specified.
DbMemoryException If the requested item could not be returned due to insufficient memory, the Db.get method will fail and throw a DbMemoryException exception.
Returns:
  • DB_KEYEMPTY

    The Db.get method will return Db.DB_KEYEMPTY if the database is a Queue or Recno database and the specified key exists, but was never explicitly created by the application or was later deleted.

Unless otherwise specified, the Db.get method throws an exception that encapsulates a non-zero error value on failure.

Definition at line 3770 of file Db.java.

Referenced by com::sleepycat::bdb::DataDb::get().

                                                                                 {
        return db_javaJNI.Db_get__SWIG_0(swigCPtr, DbTxn.getCPtr(txnid), key, data, flags);
    }


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