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From "Pinaki Poddar (JIRA)" <j...@apache.org>
Subject [jira] Updated: (OPENJPA-305) Dynamic configuration of EntityManagerFactory
Date Tue, 18 Sep 2007 23:44:43 GMT

     [ https://issues.apache.org/jira/browse/OPENJPA-305?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Pinaki Poddar updated OPENJPA-305:
----------------------------------

    Attachment: openjpa-305.patch.1.txt

This is a proposed patch that makes few significant changes in Value-Configuration part to
support dynamic update of Configuration. Hence this is a patch for your comment/review.

1. The intents are
    a) certain Values can be marked dynamic. This allows them to be modified even after the
configuration is frozen i.e. EntityManagerFactory has issued its first EntityManager.

    b) because EntityManagerFactories are cached based on the keys of their configuration,
the hashCode of the configuration must not be changed when a dynamic value V changes from
x1 to x2. 
      For example, for Configuration A, one of it's value V(A) is originally set to x1. Later
it was modified to x2.
      A.hashCode() should remain the same before and after the modification if V is dynamic.

    c) Equality: Two Configuration A and B had originally V(A)=x and V(B)=y where V is dynamic.
       Initially x!=y. That implies A not equals B. 
       Now V(B) is set to x. Does A now equals B? 
       The intended answer is no.

2. What needed to  support (1c) is notion of 'originalValue' for dynamic properties. This
patch implements by declaring a new String field in Value.class, also logic of setting this
'originalValue' in setString() and setObject() methods.

3. The 'originalValue' notion is used for changed behavior of Value.equals() and Value.hashCode()
methods.

4. ConfigurationImpl used to compute its hashCode() and equals() by first converting itself
into a Properties object. I do not why. That is the main reason this is submitted as a patch
for everyone's comment/review. 
   This patch makes a conceptual change. Now ConfigurationImpl computes its hashCode() and
equals() based on its Values -- who in turn evaluates their own hashCode() and equals() that
varies based on their dynamic nature.


          

> Dynamic configuration of EntityManagerFactory
> ---------------------------------------------
>
>                 Key: OPENJPA-305
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-305
>             Project: OpenJPA
>          Issue Type: New Feature
>            Reporter: Pinaki Poddar
>         Attachments: openjpa-305.patch.1.txt
>
>
> OpenJPA configures EntityManagerFactory at creation time via an instance of Configuartion
object. Once EntityManagerFactory is created and a EntityManager is issued from it -- the
Configuration is frozen by design. That is no further changes to Configuration is allowed
as long as EntityManagerFactory lives.
> For certain configuration properties, it is desirable to change them during the lifetime
of a EntityManagerFactory.
> This issue is raised to initiate a discussion on such a feature, the possibility and
limitations of dynamic update and track the impact of such a change as frozen Configuration
is an important assumption.
>  

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