Re: AW: [OJB-developers] Let's fix the testsuite!

[Thomas M. <tho...@ho...>]

Hi again,

Oleg Nitz wrote:

> Hi Thomas,
> 
> On Tuesday 28 May 2002 10:14, Mahler Thomas wrote:
> 
>>>But maybe there are some problems with this?
>>>
>>I don't see any. in storeMtoNImplementor() we should check if an entry
>>already exists. If so do nothing, else insert a new entry.
>>
> No you mean repetitive database lookups? 


yes, that's ugly, that's why I implemented it the "easy" way initially...


> 
>>>BTW I wonder if the current algorithm works when some link
>>>between Persons
>>>and Projects is removed.
>>>
>>Currently there is no support to remove m:n entries automatically. They
>>have to be deleted manually.
>>
> I see. To achieve this we should either remember the original state of the 
> m:n relation or to read the set of all indirection instances from the 
> database in storeMtoNImplementor(), then compare them against the current set 
> of indirection instances in memory, then insert/delete the two differences of 
> two sets. Then there is no need in multiple database lookups.
> 


This sounds good, but we must be very careful wrt. to concurrent 
transaction.

The basic design of a broker is to be an stateless service. Of course a 
broker has a transaction state, but is does not know anything about the 
state of persistent instances. Once we start to store object state 
information within the broker we'll need a lot more thinking.
(concurrent transactions, broker pooling mechanism, cache 
synchronization accross JVM, setc.)

A much simpler aproach:
before inserting entries for a given relation in storeMtoNImplementor(), 
just delete all existing entries.
This way we
- can avoid exception caused by failing inserts,
- won't need to track object state to detect removed entries.
Overhead should be rather small we'll need to execute only one DELETE 
statement.


what do you think?


Thomas




> 
>>I'll have a look at 4. and 5. then!
>>
> Okay! :)
> 
> Thanks,
>  Oleg
> 
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