What is the proper syntax to databind a class attribute in the OpenLaszlo language? - openlaszlo

Question

I am developing a class where I wish to databind the attributes of a class to a dataset.
I have managed to get the following to work in the following simplified version of my class:
<class name="myclass">
<dataset name="attSettings"><settings>
<property name="applyshadow" defaultvalue="false" type="boolean" />
</settings></dataset>
<attribute name="default_applyshadow" type="boolean" value="$once{(this.attSettings.getPointer()).xpathQuery('settings/property[#name="applyshadow"]/#defaultvalue')}" />
</class>
However, this syntax is very cumbersome and does not feel right so I am wondering if there is a better way to do this.

Answer 1

This doesn't answer your question but explains why you cannot use a local dataset in your situation. When you have a local dataset in a class, the dataset can only be addressed in children of the class, e.g.:
<canvas debug="true">
<class name="myclass">
<dataset name="myds">
<root>
<property name="applyshadow" defaultvalue="false" type="boolean" />
</root>
</dataset>
<text datapath="local:classroot.myds:/root/property[#name='applyshadow']/#defaultvalue" />
</class>
<myclass />
</canvas>
The <text> element can access the dataset of the parent class by prepending local: to the datapath value. If you don't select a name for your dataset, OpenLaszlo will automatically use the name localdata for the dataset. Datasets using that name can be addressed by omitting the dataset name in the datapath/xpath value, e.g.
<class name="myclass">
<dataset>
<root>
<property name="applyshadow" defaultvalue="false" type="boolean" />
</root>
</dataset>
<text datapath="local:classroot:/root/property[#name='applyshadow']/#defaultvalue" />
</class>
Note that the datapath does not have a name and that the datapath used for the <text> component is now local:classroot:/root/..., while local:classroot.localdata:/root/... would work as well.
I don't understand the design decision which makes it impossible to allow the use a local dataset in the datapath of a class containing that dataset, but maybe there were some technical reasons (initialization order, etc.) for it.

Answer 2

I figured out the proper syntax to do what I wanted:
<dataset name="myclass_settings">
<root>
<property name="applyshadow" defaultvalue="false" type="boolean" />
</root>
</dataset>
<class name="myclass" datapath="myclass_settings:/root">
<attribute name="default_applyshadow" type="boolean" value=$path{'property[#name="applyshadow"]/#defaultvalue'}" />
</class>
The $path{} constraint is used on the class attribute to link the value to the dataset via a relative xpath query. I also had to move the dataset outside of the class to get it to work.