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https://issues.apache.org/jira/browse/TAPESTRY-1408?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jesse Kuhnert updated TAPESTRY-1408:
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Fix Version/s: 4.2
> Breakup @InitialValue functionality
> -----------------------------------
>
> Key: TAPESTRY-1408
> URL: https://issues.apache.org/jira/browse/TAPESTRY-1408
> Project: Tapestry
> Issue Type: Improvement
> Components: Annotations
> Affects Versions: 4.1.2
> Reporter: Patrick Moore
> Fix For: 4.2
>
>
> Currently, @InitialValue is responsible for initialize a property prior to
> use and reseting the property prior to returning the component or page to the
> pool.
> This has some negative aspects:
> 1) If InitialValue specifies a non-null value, extra objects occupy memory.
> 2) InitialValue cannot refer to anything that might result in a large graph
> of objects (for example a db query result) as this graph will remain after
> the processing is complete.
> 3) @Persist("session") + @InitialValue() semantics are unclear.
> I propose that @InitialValue be modified so that it takes a second argument:
> @InitialValue(pre-use-value, reset-value)
> "pre-use-value" - assigned to the property prior to the first attempt to use
> the property.
> "reset-value" - assigned to the property prior to the component/page being
> returned to the pool ( default: null)
> InitialValue would be changed so that it acts the first time the property's
> get method is called, provided the property doesn't already have a value set
> by another annotation ( @Persist("session") ) or some other reason (tapestry
> experts fill in that some-other-reason here ). InitialValue would set the
> propert by using the property's set() method rather than setting it directly
> (I think this is what is done today)
> When the component/page is returned to the pool, the 'reset-value' would be
> used. When reseting the property, InitialValue should not use the property's
> set() method, but would set the field variable directly.
> What would this mean? This would eliminate many uses "prepareForRender()"
> methods. Also eliminated would be the if ( == null ) { } initialization
> boilerplate done in a property's get() . Both could be replaced by:
> @InitialValue("dataFromDB")
> // or @InitialValue("getDataFromDB()")
> public abstract MyData getData();
> protected MyData getDataFromDB() {
> // hard work here
> }
> In the html, the user would just refer to the 'data' property. If due to
> conditional blocks the 'data' property was never accessed, then
> getDataFromDB() is never called either.
> This would also allow @Persist + @InitialValue to work together. InitialValue
> does its thing when accessed and it would invoke the set() method on the
> property to trigger any session persistence.
> If there are backward compatability issues, could a new annotation be created?
> This change would help make initializing components/pages flow more naturally.
> Thanks....
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