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From "Albert Lee (JIRA)" <j...@apache.org>
Subject [jira] Commented: (OPENJPA-910) Allow multiple keys for the same property to be specified at different levels
Date Fri, 06 Feb 2009 21:48:59 GMT

    [ https://issues.apache.org/jira/browse/OPENJPA-910?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12671345#action_12671345
] 

Albert Lee commented on OPENJPA-910:
------------------------------------

>> Rule 3: If the same key is specified at the same level, a error message is generated.


Throwing an exception seems too harsh for the following reasons:

1) Rule 2 says: "All monikers for a key are treated as interchangeable for all purpose.....",
so we should treated all property instances the same.
2) Based on 1), one property can override other, even with different prefix, at different
levels. For consistency, this should work the same at the same level
3) If 2 instances of the SAME property is specified in the same level, openjpa currently will
take the last instance's value, so I lean toward keeping the same behavior.
4) The argument against 3) is which instance of the multiple definitions will be used and
how will user know which one is picked deterministically by openjpa. hence the proposed rule
3, thrown an exception. To address the concern, a warning can be issued indicating the value
accepted and used by openjpa configuration would be sufficient.

Albert Lee.

> Allow multiple keys for the same property to be specified at different levels
> -----------------------------------------------------------------------------
>
>                 Key: OPENJPA-910
>                 URL: https://issues.apache.org/jira/browse/OPENJPA-910
>             Project: OpenJPA
>          Issue Type: Improvement
>          Components: kernel
>    Affects Versions: 2.0.0-M1
>            Reporter: Dianne Richards
>            Priority: Minor
>             Fix For: 2.0.0
>
>
> In OPENJPA-850, support was provided for some 2.0 spec properties. Some of these properties
are equivalent to current openjpa properties, resulting in some properties supported by 2
different keys. As part of this enhancement, an exception is thrown if the same property is
specified more than once with different keys. An issue has been raised related to this suggesting
that one key could be specified at one level (such as the persistence.xml) but another key
could be specified at another level (such as a system property), and that we should allow
this. This was discussed among several people, with the resulting conclusion documented by
Pinaki as follows:
> Rule 1: OpenJPA configurations can be specified at following levels (from lowest to highest)
> I have changed Mike's order to reflect how the code (perhaps) now uses precedence (changing
such order may require hard tweaks)
> > 1. openjpa.xml (globals)
> > 5. java.lang.System.getProperties()  
> > 2. persistence.xml (<properties></properties>)
> > 3. A map passed in to the call to createEntityManagerFactory()
> > 4. A map passed in to getEntityManager() 
> Rule 2: Each property is identified by a key. A key must have one, but can have multiple
monikers. For example, 'ConnectionDriver' property has two monikers 'openjpa.ConnectionDriverName'
and 'javax.persistence.jdbc.driver'. All monikers for a key are treated as interchangeable
for all purpose other than when a key appears in the returned list of EMF.getProperties()
-- which is always the moniker whose corresponding value is 'in effect' in the configuration.
> Rule 3: If the same key is specified at the same level, a error message is generated.
> Rule 4: If the same key is specified at different levels, the higher level value overwrite
the lower level value. 
> INFO/TRACE message is printed if the values are overwritten or attempted to be overwritten
respectively. 

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