> *** For factory sequences (not defined in the database) is the API > sufficient to use the sequence in the three modes: nontransactional, > contiguous, and noncontiguous? ***
Well, the implementation has to call factory.newInstance() to create the sequence, but has no way of telling the factory whether it wants a contiguous, noncontiguous, or nontransactional sequence. Really depends whether the users sequence that is created by the factory will typically be able to operate in all 3 strategies. I would guess that most sequences would support one of the 3 strategies, so by saying that they want to use a particular factory, then they are implicitly electing the strategy that will be used. If it is really necessary to allow a factory to create a sequence in any of the 3 strategies then we could add a requirement on the factory of having a static newInstance(int strategy) method, and the "strategy" value specified in the metadata could be passed in. If the metadata has no value for strategy then the newInstance() method is called. > *** Does Derby support sequences? *** No. DB2, PostgreSQL, Oracle, Firebird, SAPDB, McKoi and maybe some others do. The JDO impl can clearly generate a sequence using other means where there is no native RDBMS support. -- Andy
