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Sourcecode: db4.2 version File versions  Download package

Dbc com::sleepycat::db::Db::join ( Dbc[]  curslist,
int  flags 
) throws DbException [inline]

The Db.join method creates a specialized join cursor for use in performing equality or natural joins on secondary indices. For information on how to organize your data to use this functionality, see Equality join .

The Db.join method method is called using the Db handle of the primary database.

The join cursor supports only the Dbc.get and dbc_close cursor functions:

Iterates over the values associated with the keys to which each item in curslist was initialized. Any data value that appears in all items specified by the curslist parameter is then used as a key into the primary , and the key/data pair found in the primary is returned. The flags parameter must be set to 0 or the following value: In addition, the following flag may be set by bitwise inclusively OR 'ing it into the flags parameter: Close the returned cursor and release all resources. (Closing the cursors in curslist is the responsibility of the caller.)

curslist The curslist parameter contains a null terminated array of cursors. Each cursor must have been initialized to refer to the key on which the underlying database should be joined. Typically, this initialization is done by a Dbc.get call with the Db.DB_SET flag specified. Once the cursors have been passed as part of a curslist , they should not be accessed or modified until the newly created join cursor has been closed, or else inconsistent results may be returned.

Joined values are retrieved by doing a sequential iteration over the first cursor in the curslist parameter, and a nested iteration over each secondary cursor in the order they are specified in the curslist parameter. This requires database traversals to search for the current datum in all the cursors after the first. For this reason, the best join performance normally results from sorting the cursors from the one that refers to the least number of data items to the one that refers to the most. By default, Db.join does this sort on behalf of its caller.

For the returned join cursor to be used in a transaction-protected manner, the cursors listed in curslist must have been created within the context of the same transaction.

flags must be set to 0 or the following value:

    Do not sort the cursors based on the number of data items to which they refer. If the data are structured so that cursors with many data items also share many common elements, higher performance will result from listing those cursors before cursors with fewer data items; that is, a sort order other than the default. The Db.DB_JOIN_NOSORT flag permits applications to perform join optimization prior to calling Db.join.

DbException The Db.join method may fail and throw DbException, encapsulating one of the following non-zero errors:
IllegalArgumentException The Db.join method will fail and throw a IllegalArgumentException exception if cursor methods other than Dbc.get or Dbc.close were called; or if an invalid flag value or parameter was specified.
The Db.join method throws an exception that encapsulates a non-zero error value on failure.

Definition at line 4425 of file Db.java.

        long cPtr = db_javaJNI.Db_join(swigCPtr, curslist, flags);
        return (cPtr == 0) ? null : new Dbc(cPtr, true);

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