[hibernate-issues] [Hibernate-JIRA] Issue Comment Edited: (HHH-2896) unified approach for id and natural-id loading

[Eric Dalquist (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2896?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=43830#comment-43830 ] 

Eric Dalquist edited comment on HHH-2896 at 9/28/11 2:39 PM:
-------------------------------------------------------------

SessionImpl will be restructured to make IdentifierLoadAccess the first-class method of retrieving entities by primary key. All existing load and get methods will be updated to delegate to IdentifierLoadAccess.

The initial implementation of NaturalIdLoadAccess will be a two-step process which includes the creation of a new ResolveNaturalIdEvent event type.
# Fire a ResolveNaturalIdEvent with the entity name and natural id attribute values. This event will resolve the primary key for the entity.
# Fire a LoadEvent using the resolved primary key and provided lock options.

A new cache to store the NaturalId->PK mappings is needed, it will be named [entityName].naturalId. This cache will be similar to a query cache in functionality, lookups by immutable natural id will never do an isUpToDate check, lookups on mutable natural id's will behave very similarly to existing query cached lookups.

The hibernate persist logic will need to be reviewed for its handling of immutable natural id attributes. These attributes should never be included in generated SQL update statements to enforce the immutability constraint of the natural id.

New methods to manage this new cache will need to be added to org.hibernate.Cache
{code:java}
evictNaturalKeyEntry(String entityName, Object key)
evictNaturalKeyRegion(String entityName)
{code}

Improvements that can be planned out beyond the initial feature implementation
* Extend the handling of ResolveNaturalIdEvent to load the entity into the session cache if it is not already present, this should reduce the number of db queries by 1 for each naturalid load that is a cache-miss.
* Add handling of the various persist/load/merge/delete events to maintain the NaturalID->PK mappings in this new cache.

      was (Author: edalquist):
    SessionImpl will be restructured to make IdentifierLoadAccess the first-class method of retrieving entities by primary key. All existing load and get methods will be updated to delegate to IdentifierLoadAccess.

The initial implementation of NaturalIdLoadAccess will be a two-step process which includes the creation of a new ResolveNaturalIdEvent event type.
# Fire a ResolveNaturalIdEvent with the entity name and natural id attribute values. This event will resolve the primary key for the entity.
# Fire a LoadEvent using the resolved primary key and provided lock options.

A new cache to store the NaturalId->PK mappings is needed, it will be named [entityName].[naturalId]. This cache will be similar to a query cache in functionality, lookups by immutable natural id will never do an isUpToDate check, lookups on mutable natural id's will behave very similarly to existing query cached lookups.

The hibernate persist logic will need to be reviewed for its handling of immutable natural id attributes. These attributes should never be included in generated SQL update statements to enforce the immutability constraint of the natural id.

New methods to manage this new cache will need to be added to org.hibernate.Cache
{code:java}
evictNaturalKeyEntry(String entityName, Object key)
evictNaturalKeyRegion(String entityName)
{code}

Improvements that can be planned out beyond the initial feature implementation
* Extend the handling of ResolveNaturalIdEvent to load the entity into the session cache if it is not already present, this should reduce the number of db queries by 1 for each naturalid load that is a cache-miss.
* Add handling of the various persist/load/merge/delete events to maintain the NaturalID->PK mappings in this new cache.
  
>  unified approach for id and natural-id loading
> -----------------------------------------------
>
>                 Key: HHH-2896
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2896
>             Project: Hibernate Core
>          Issue Type: Improvement
>          Components: core
>            Reporter: Steve Ebersole
>            Assignee: Steve Ebersole
>             Fix For: 3.x
>
>         Attachments: hhh-2896_irc_discussion.txt
>
>
> A follow-on to HHH-2879 in regards to unifying the loading of entities by pk or natural-id.

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