[cdi-dev] Support Request (and Conversation?) Scope in @Singleton @Startup @PostConstruct methods

[Mark Struberg]

Stu, 

usually a select for update is done _explicitely_ to prevent others from doing something with this entity. We do not have control whether this is good or not.

I do agree with you that this should barely be used in a webapp, because sometimes this can even lead to a table-lock (some dbs cannot do a simple record lock without either locking the page or sometimes even the whole table).

Imo this functionality should NEVER have added to the EntityManager but might have been provided via a separate API, etc. But that's how it is currently :/

But this is not the only reason why the EM is not Serializable. If you did serialize an old Hibernate-2 EM then you lost all the non-persistent status. This doesn't sound sane neither...


LieGrue,
strub



----- Original Message -----
> From: Stuart Douglas <stuart.w.douglas at gmail.com>
> To: Mark Struberg <struberg at yahoo.de>
> Cc: Christian Bauer <christian.bauer at gmail.com>; "cdi-dev at lists.jboss.org" <cdi-dev at lists.jboss.org>
> Sent: Thursday, March 15, 2012 12:34 PM
> Subject: Re: [cdi-dev] Support Request (and Conversation?) Scope in @Singleton @Startup @PostConstruct methods
> 
> 
> On 15/03/2012, at 10:26 PM, Mark Struberg wrote:
> 
>>  Simply as that: as the EntityManager per spec doesn't implement 
> Serializable.
>> 
>> 
>>  Also the EJB spec explicitely states it as well in Section 4.2:
>>>  - A container must not passivate a stateful session bean with an 
> extended 
>>>  persistence context unless ...
>> 
>> 
>>  Thus an Extended EM doesn't need to be Serializable. If you build a 
> feature based on the assumption that each EntityManager is Serializable, then it 
> will result in non-portable behaviour.
>> 
>>  Well, in JPA-1 it would at least have been possible to implement a 
> Serializable EM, but in JPA2 you are mostly out of luck.
>> 
>>  There are tons of indicators. As an example: how would you serialize an 
> EntityManager which holds a pessimistic lock() on the database? ^^
> 
> If you are holding a lock longer that a request you are doing something wrong. 
> As you are probably not going to want to serialise the entity manager in the 
> middle of a request it should be possible to work around it. 
> 
> Also not everyone uses HA clusters or persistent sessions, so the conversation 
> scope is not always actually serialised. 
> 
> There are still a lot of use cases for this, but it obviously there are 
> limitations.
> 
> Stuart
> 
> 
>> 
>>  LieGrue,
>>  strub
>> 
>> 
>> 
>> 
>>  ----- Original Message -----
>>>  From: Christian Bauer <christian.bauer at gmail.com>
>>>  To: cdi-dev at lists.jboss.org
>>>  Cc: 
>>>  Sent: Thursday, March 15, 2012 9:18 AM
>>>  Subject: Re: [cdi-dev] Support Request (and Conversation?) Scope in 
> @Singleton @Startup @PostConstruct methods
>>> 
>>> 
>>>  On Mar 6, 2012, at 2:58 , Mark Struberg wrote:
>>> 
>>>>  The EM is per JPA spec NOT Serializable and thus must not get 
> stored in the 
>>>  Session.
>>> 
>>>  Chapter and section?
>>> 
>>> 
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