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From "Dan Adams (JIRA)" <...@tapestry.apache.org>
Subject [jira] Created: (TAPESTRY-2244) Add @Once annotiation for caching method values
Date Sat, 08 Mar 2008 13:33:46 GMT
Add @Once annotiation for caching method values
-----------------------------------------------

                 Key: TAPESTRY-2244
                 URL: https://issues.apache.org/jira/browse/TAPESTRY-2244
             Project: Tapestry
          Issue Type: New Feature
          Components: tapestry-core
    Affects Versions: 5.0.11
            Reporter: Dan Adams
            Assignee: Dan Adams


The @Once annotation can be used on methods to cache the value or cache the value based on
some other value changing (great for loops). We've been using it in our internal CMS library
and it's immensly useful, especially when getting things out of any kind of database or doing
queries. Here's a typical usage:

class:
@Once
public List<Entities> getEntities() {
  // get and return the objects from the database or something
}

in the template:
<t:if test="!entities.empty">
  do something
</t:if>

<t:loop source="entities">
  loop through and do something
</t:loop>

In this example, getEntities gets cached on the if test and then the value is cached so it
doesn't get called again on the loop. You can also use it this way:

@Property
private Entity loopValue;

@Once(watch="loopValue")
public Object getSomeDependentValue() {
  // do some expensive operation based on loopValue
}

which will only execute the method each time loopValue changes.

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