[OJB-developers] New update lock mechanism

[<Car...@vi...>]

Hi,

we are using OJB to access an existing db and it works create. But now we
came to a point where we would like to implement some locking for updates to
prevent users from destroying there data each other. (concurrency problem )
BRJ has implemented a locking mechanism for optimistic locking and I think
it works create if you have extra columns in the database for locking such
as version fields etc. 
Unfortunately the database we have to access does not have any special
fields for a locking mechanism. So we would like to implement the locking
via the changed attributes and manipulate the update statement in that way
that we enhance the filter criteria so that the changed values must have the
original value in the database. 

Example:
   UPDATE <table> set Field1=<newValue> where pk=<pkValue> AND
Field1=<oldValue>;

To get this work the locking mechanism must be implemented outside from OJB.


My first idea is to define an UpdateLockManager- Interface. Such an ULM can
be registered to the Class in the ClassDescriptor. If the JDBCAccess-Class
finds a ULM for a specific class in the executeUpdate-Method than it would
get a ready bound PreparedStatement from the ULM and executes it. Otherwise
everything will work as now. 
The strategy do register an ULM in the repository would minimize the changes
in OJB but could bring many threading problems to the implementation of the
ULM. Another way could be to define another update-Method in the broker
interface where you can give an ULM per call. This surely makes the
threadsafe implementation of an ULM easier.
Maybe it is helpful for the ULM to get some call backs from the
ClassDescriptor or from the broker if something happens with the objects. So
a Listener interface on the broker could be useful as well.

What do you think about the ideas?

sp...@vi...