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From "Craig L Russell (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (JDO-617) JDOQL : Bulk Update and Delete Operations
Date Fri, 06 Apr 2012 21:36:17 GMT

    [ https://issues.apache.org/jira/browse/JDO-617?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13248893#comment-13248893
] 

Craig L Russell commented on JDO-617:
-------------------------------------

I don't see the value in adding update by query to JDO, either in the query language or in
the typesafe query methods. What we have defined already is using a query language to select
a number of items to operate on (either read into memory or delete). Once you have the list
of items, you iterate the list and perform some algorithm on the items using the native methods
of the memory language, Java. Any changes will be reflected in the datastore if you commit
the transaction. 

In contrast, specifying a Java algorithm to execute on all selected items from the datastore
is fraught. Simply providing a constant new value for selected fields doesn't seem very useful.
There are ways of specifying a Java algorithm to operate on some items, and passing the algorithm
to the query method. For example, passing a "function object" (Runnable) to the query, and
expecting the function object to be applied to each item in the result. The implementation
would need to read the byte codes of the "function object" to figure out exactly what the
function was doing and try to apply that function to the datastore objects. 

But I suspect that even this small bit of functionality won't be worth the considerable effort
to implement. 

Bottom line, while I appreciate that there are many places where there is a natural mapping
between a subset of Java that is useful to filter objects from a datastore and the corresponding
datastore language, update is not one of these places.
                
> JDOQL : Bulk Update and Delete Operations
> -----------------------------------------
>
>                 Key: JDO-617
>                 URL: https://issues.apache.org/jira/browse/JDO-617
>             Project: JDO
>          Issue Type: New Feature
>            Reporter: Eric SULTAN
>
> It would be usefull that the JDO Query Langage could do some UPDATE and DELETE on Persistent
Object like this :
> UPDATE [<candidate-class>] SET item1=<newValue>, item2=<newValue> [WHERE
<filter>]
> The new_value specified for an update operation must be compatible in type with the state-field
to
> which it is assigned.
> Bulk Update must modify the value of the version column and refresh Level1 and Level2
cache.
> DELETE FROM [<candidate-class>] [WHERE <filter>]
> By default Bulk Delete is appy on the specified class and its subclasses and doesn't
do cascade delete.
> A keyword like CASCADE must be set if we want to does a cascade delete : 
> DELETE CASCADE FROM [<candidate-class>] [WHERE <filter>]

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