Oliver’s Place

Did you ever had to implement a menu in Grails GSP where every link element should be seperated from its predecessor by a separator character and where some of the elements can be missing when certain conditions are not met (security etc)?

The part with the optional elements can turn the separator handling into a real mess. So today I decided to end this nonsense. The result is a tiny taglib which can be integrated into every grails project. The usage is pretty self explanatory:

<mx:toolbar separator=’|'>
  <mx:item>
    <shiro:hasPermission permission=”topic:delete”>
      <g:link controller=”topic” action=”delete” id=”${topic.id}”><g:message code=”topic.delete”></g:message></g:link>
    </shiro:hasPermission>
  </mx:item>

  <mx:item>
    <shiro:hasPermission permission=”topic:lock”>
      <g:link controller=”topic” action=”lock” id=”${topic.id}”><g:message code=”topic.lock”></g:message></g:link>
    </shiro:hasPermission>
  </mx:item>
</mx:toolbar>

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The other day I was writing a medium complex HQL query for a Grails App and no matter what the line executing the query would crash like this:

java.lang.NullPointerException
	at $Proxy13.createQuery(Unknown Source)
	at com.acme.PerformanceService.makePerformanceSheet(PerformanceService.groovy:38)
  ...

So how the hell do we figure out what the problem given so few information? Turns out that grails sanitizes the exception stacktrace, resulting in better readability by removing a lot of clutter. Sometimes though this optimization will also hide some important details from you. Luckily we can still refer to stacktrace.log which usually resides in the project root folder in development mode. In this particular case opening the file reveiled this:

java.lang.NullPointerException
	at org.hibernate.dialect.Dialect$3.getReturnType(Dialect.java:125)
	at org.hibernate.hql.ast.util.SessionFactoryHelper.findFunctionReturnType(SessionFactoryHelper.java:405)
	at org.hibernate.hql.ast.tree.AggregateNode.getDataType(AggregateNode.java:44)
	at org.hibernate.hql.ast.tree.SelectClause.initializeExplicitSelectClause(SelectClause.java:165)
	at org.hibernate.hql.ast.HqlSqlWalker.useSelectClause(HqlSqlWalker.java:727)
	at org.hibernate.hql.ast.HqlSqlWalker.processQuery(HqlSqlWalker.java:551)
	at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:645)
	at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:281)
	at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:229)
	at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:251)
	at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:183)
	at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:134)
	at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:101)
	at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
	at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:94)
	at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:156)
	at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:135)
  ...

Which almost instantly gave me the hint that something’s wrong with the aggregate part of my query:

org.hibernate.hql.ast.tree.AggregateNode.getDataType

And indeed the problem was that I had ported an SQL Query to HQL and forgot to rename the sum() aggregate argument from the column name to the domain class property name:

sum(some_property) instead of sum(foo.someProperty)

Every Web Application Project I’ve been involved in the recent past had one thing in common: the client demanded more and more rich-client features at an ever increasing pace – without committing itself to real rich-client frameworks such as Flex or Silverlight. This leaves us with Javascript / AJAX for implementing highly dynamic User Interfaces for Web Applications. A very common problem when working with Ajax is the requirement to update multiple parts of a page in response to a single request. This post aims to familiarize the reader with my own approach to this problem.

At its core my solution consists of just two functions – one running server side and the other executing on the client. The first function is intended to run on the server and is written in Groovy. It was originally written in Python for use with the Django framework and I’ve ported it to Groovy when I switched to Grails as my primary RAD Web framework. This function takes a map as argument and returns a JSON encoded map where the key is a valid jQuery Selector designating the targets for the update and the value is a map containing information how the matched elements should be modified and how the content for the update shall be produced. Don’t worry if you find this confusing at first. There’s a sample further down.

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I’ve been doing a serious amount of Grails Development lately and if there’s one Grails Plugin I consider mandatory for any serious production deployment then it is the UI-Performance plugin by Burt Beckwith. One of the features of the plugin that reduces server load is versioning and far-future “Expires” and “Cache-Control” headers for static resources.

Each time you generate a new WAR for deployment, a new version is applied to all image, .js, and .css files so files can be cached forever. The next time you deploy a new version of your application, all of the resource file names will have changed, so only then will files be requested. The default process for determining the version is to look at the version of the root project folder in the Subversion metadata files. Since I’ve switched to GIT for all my projects a while ago the plugin would fallback to “System.currentTimeMillis().toString()” to compute the version.

My solution is to include the following line in my projects Config.groovy:

uiperformance.determineVersion = { -> "git rev-list --max-count=1 HEAD".execute().text.trim() }

This allows the HEAD commit SHA1 hash of the current branch to be used as the uiperformance version for deployment.