[hibernate-issues] [Hibernate-JIRA] Updated: (HV-230) Database Connective or @Unique

[Hardy Ferentschik (JIRA)]

     [ http://opensource.atlassian.com/projects/hibernate/browse/HV-230?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Hardy Ferentschik updated HV-230:
---------------------------------

    Attachment: HV-230.patch

Attaching a patch which shows how a {{@Unique}} constraint could be implemented using the "open temporary session on top of current session's connection" approach. Included in the patch is a {{SessionAwareConstraintValidatorFactory}}. We could add a check into {{BeanValidationEventListener.validate}} to see which type the current factory is and if it is the {{SessionAwareConstraintValidatorFactory}} inject the {{SessionFactory}} automatically. 
The reason I am not committing this patch yet is that introducing the {{@Unique}} creates some problems.  Most importantly there might be [phantom reads|http://en.wikipedia.org/wiki/Isolation_%28database_systems%29#Repeatable_reads_.28phantom_reads.29]. If we add {{@Unique}} as custom constraint we need to make sure that we add appropriate warning notes to the documentation.
The alternative is to provide the sample code on the Validator [wiki|http://community.jboss.org/en/hibernate/validator]

> Database Connective or @Unique
> ------------------------------
>
>                 Key: HV-230
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HV-230
>             Project: Hibernate Validator
>          Issue Type: New Feature
>          Components: validators
>    Affects Versions: 3.1.0.GA
>            Reporter: Ken Egervari
>            Priority: Critical
>             Fix For: 4.1.0
>
>         Attachments: HV-230.patch
>
>
> I find a common validation use case is checking to see if a field is unique to all those in the table, such as emails, isbns, usernames, keywords, etc. these fields may not be the primary key, but still need to be unique.
> It would be fantastic if hibernate validator implemented this.
> This is a common problem though because the domain class will need to have access the database. I dunno if there's an easy way to wire in a copy of sessionFactory to make this easy to write.
> Perhaps something like this:
> @Query( "select user from User user where user.emailAddress = :this.emailAddress and user.id != :this.id", message = "That Email is already being used by another user in the system" )
> private String emailAddress;
> Basically the idea is that if @Query returns no results, then the validation constraint is good, and if returns more than 1 result, then it fails. Kind of like simpleJdbcTemplate.queryForMap() does within the Spring testing framework. That method causes the test to fail if no row is returned, because it expects 1 result.
> If it were possible to just say
> @Unique
> private String emailAddress;
> That would be extremely concise and would save people a ton of time. 
> Of course, this requires some interoperability with Hibernate... but I think that's a good thing, no?
> Thanks for taking this into consideration. I'd appreciate an email letting me know how to do this in a clean way in 3.1.0 GA as it is as well if you would. Thank you.

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