Re: [eclipselink-users] SessionCustomizer to modify/detect database plat

[Tom Ware <tom.ware@xxxxxxxxxx>]

Hi Laird,

  It looks like the use-case where you want auto-detection of database platform 
for all but a single platform is not well covered by the current code base.  I 
see you've filed bug 401388 for this issue.  The easiest way for us to address 
your specific issue is to make the isInformixOuterJoin flag a boolean on the 
InformixPlatform that could be set in your customizer, this could be done 
quickly, but would not help you for your 2.3.2 deployment.

  The possible workarounds I see are:

1. Pass the new platform as a property when your EntityManagerFactory is created
2. Try to override the auto-detection yourself.  This would involve roughly the 
following steps
  - Use the eclipselink.target-database property in your persistence.xml to set 
a platform... Any platform. (this setting will make EclipseLink avoid it's own 
auto-detection code)
  - In a prelogin event use the code from our 
DatabaseSessionImpl.loginAndDetectDatasource method to use our auto-detection 
code and then override the InformixPlatform if it is detected.  Here is the code 
as it exists.  You could override the platformName if it was the InformixPlatform:

--
                try {
                    String vendorNameAndVersion = 
conn.getMetaData().getDatabaseProductName() + 
conn.getMetaData().getDatabaseMajorVersion();
                    platformName = 
DBPlatformHelper.getDBPlatform(vendorNameAndVersion, getSessionLog());
                    getLogin().setPlatformClassName(platformName);
                } catch (EclipseLinkException classNotFound) {
                    if (platformName.indexOf("Oracle") != -1) {
                        // If we are running against Oracle, it is possible 
that we are running in an environment where
                        // the OracleXPlatform class can not be loaded. Try 
using OraclePlatform class before giving up

getLogin().setPlatformClassName(OraclePlatform.class.getName());
                    } else {
                        throw classNotFound;
                    }
                }
--

Sorry this is so involved.

-Tom

On 21/02/2013 1:43 AM, Laird Nelson wrote:
> Is it possible to write a SessionCustomizer that jumps in early enough to
> install a custom platform on a session, AND that is immune to the platform's
> jettisoning of any installed platform upon initial login?
>
> One of the first things that DatabaseSessionImpl.java does is to set the
> session's associated platform--conveniently installed by my session
> customizer--to null.  WTF.
>
> In other words, a SessionCustomizer that I've written happily installs a new
> platform...which is then immediately overwritten by the core EclipseLink
> innards.  I see no way to prevent this overwriting.
>
> A SessionEventListener which activates after a postLogin() event that does the
> same thing results in dozens of NullPointerExceptions from deep within
> QuerySequence.java later on in the persistence unit lifecycle, so that's not an
> option.
>
> Relevant StackOverflow question:
> http://stackoverflow.com/questions/14899458/what-is-the-proper-way-to-have-a-user-authored-eclipselink-databaseplatform-subc
>
> Best,
> Laird
>
> --
> http://about.me/lairdnelson
>
>
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