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From Evgeny Ryabitskiy <evgeny.ryabits...@gmail.com>
Subject Re: Singletons in Cayenne and problems. Can I use multiple transactions?
Date Tue, 01 Dec 2009 13:27:55 GMT
Problem in multiple Domains.
When I am creating transaction I am creating it's for specific
DataDomain (like a DataContext).
When I have 2 Modules with dedicated DataDomains (so it will be 2
DataDomains) I can create 2 Transactions
(domain.createTransaction()).

But to thread I can bind only one. Then when I start performing queries I got:
1)First Domain Transaction is binded and handled normally
2)Second Domain Transaction is override by first DataDomain. So when I
perform query for second: ThreadLocals return Transaction for firs
Domain.

Evgeny



2009/12/1 Andrus Adamchik <andrus@objectstyle.org>:
> Singletons are bad in a general purpose framework, like Cayenne. No question
> about that. Per your description even thread-local singletons can be a
> problem, which is less obvious to me, but I guess real in some
> circumstances. So let's see what those are.
>
>> 2)DataContext.getThreadLocal()
>> Solved by own ThreadLocal for each module. (modules can work in one
>> thread)
>> //also spend some time
>
> This is just a convenience in Cayenne. Nobody's forced to use it. I will go
> as far as to suggest to remove it from Cayenne 3.1 as a built-in feature,
> and just document it as a possible design pattern in a user application.
>
>> 3)Transaction.getThreadTransaction()
>> this is killing one!!!
>> using of own ThreadLocal doesn't help.
>> It's hard-coded in performing Query to use this singleton
>> Transaction.getThreadTransaction()
>> And that is really huge problem for me.
>
> J2EE pattern of tying a transaction to an execution thread, even if multiple
> data sources are involved, makes sense as it allows to commit/rollback
> multiple things at once. Cayenne Transaction sort of follows that. JDBC
> connections within the transaction are scoped by DataNode name. So what
> exactly is the problem?
>
> Andrus
>
>
>
> On Dec 1, 2009, at 2:44 PM, Evgeny Ryabitskiy wrote:
>
>> Hello 2 everyone!
>>
>> Today I one more time thinking about singleton pattern and it's hard
>> usssage in Cayenne.
>>
>> So.. I have several modules, each has own DomainConfig file and
>> connection to it's DataBase. Sometimes there can be used different DB
>> servers and even different DB types (usually it's Oracle and MS SQL,
>> sometimes Sybase).
>>
>> Singletons:
>> 1) Configuration.getSharedConfiguration()
>> This problem is solved:
>> DefaultConfiguration conf = new
>> DefaultConfiguration("module1-cayenne.xml");
>> conf .initialize;
>> conf.getDomain();
>> //spend some time to find solution... everywhere examples with
>> SharedConfiguration
>>
>> 2)DataContext.getThreadLocal()
>> Solved by own ThreadLocal for each module. (modules can work in one
>> thread)
>> //also spend some time
>>
>> 3)Transaction.getThreadTransaction()
>> this is killing one!!!
>> using of own ThreadLocal doesn't help.
>> It's hard-coded in performing Query to use this singleton
>> Transaction.getThreadTransaction()
>> And that is really huge problem for me.
>>
>> So me suggestion is to move this ThreadLocal to DataDomain. Still can
>> use singleton API for standalone applications.
>> Also we can move DataContext to DataDomain.
>>
>> Evgeny.
>>
>
>

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