zkgrails - LoadOnDemand

?

This is a ZKGrails port of the program written in?http://docs.zkoss.org/wiki/Use_Load-On-Demand_to_Handle_Huge_Data. This tutorial is working for ZKGrails 0.7.1 and later.

You need to prepare a Grails project for this tutorial by type:

$?grails create-app ondemand

Next,you need to install ZKGrails. The latest version will be installed automatically,when type:

$?grails install-plugin zk

We are going to demonstrate with a simple domain class,Employee. To create domain class in Grails,simply use the command?create-domain-class,following by your class name:

$?grails create-domain-class employee

We then add two properties into domain class Employee,namely fullname and username. Both are string.

class Employee {

? ? String fullname
? ? String username

? ? static constraints = {
? ? }
}

$?grails create-zul employee

This will also create?grails-apps/composers/EmployeeComposer.groovy?for you.

<window apply="${employeeComposer}">

? ? <vbox>
? ? ? ? <image src="images/grails_logo.jpg"/>
? ? </vbox>

? ? <listbox id="lstEmployee" width="100%" checkmark="true">
? ? ? ? <listhead sizable="true">
? ? ? ? ? ? <listheader label="ID" sort="auto" />
? ? ? ? ? ? <listheader label="Full Name" sort="auto" />
? ? ? ? ? ? <listheader label="User Name" sort="auto" />
? ? ? ? </listhead>
? </listbox>
? <paging id="pagEmployee" pageSize="30" />

</window>

From the code,you may see 2 properties?lstEmployee,and?pagEmployee. Both are injected by?GrailsComposer,which is a subclass ofGenericForwardComposer. They,apparently,represents listbox and paging components from your .zul file.

You may notice that there is?afterCompose?closure. This closure is run by doAfterCompose,and it's a Groovy place to initialize your components.

The auto-wired event handle?onPaging_pagEmployee?will be called everytime you click pagEmployee to change the active page. Note that,the only argument of the handler must be?ForwardEvent?or?Event?to make it work.

I also show you the use of Groovy's default argument value declared at?redraw?method. That is,calling?redraw()?in?afterCompose?meansredraw(0).

Also in?redraw?method,there are two places to use dynamic methods added by ZKGrails. The first one is listbox#clear,of which removes all listitem. The second one is append,which accepts component construction via ZK Builder.

import org.zkoss.zkgrails.*
import org.zkoss.zk.ui.event.*

class EmployeeComposer extends GrailsComposer {

? ? def lstEmployee
? ? def pagEmployee

? ? def afterCompose = { c ->
? ? ? ? pagEmployee.totalSize = Employee.count()
? ? ? ? redraw()
? ? }

? ? def onPaging_pagEmployee(ForwardEvent fe) {
? ? ? ? def e = fe.origin
? ? ? ? redraw(e.activePage)
? ? }

? ? def redraw(page=0) {
? ? ? ? def list = Employee.list(offset: page * pagEmployee.pageSize,
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?max: pagEmployee.pageSize)

? ? ? ? lstEmployee.clear()
? ? ? ? lstEmployee.append {
? ? ? ? ? ? list.each { e ->
? ? ? ? ? ? ? ? listitem(value: e) {
? ? ? ? ? ? ? ? ? ? listcell(label: e.id)
? ? ? ? ? ? ? ? ? ? listcell(label: e.fullname)
? ? ? ? ? ? ? ? ? ? listcell(label: e.username)
? ? ? ? ? ? ? ? }
? ? ? ? ? ? }
? ? ? ? }
? ? }

}

Before getting your application run,you need some testing data to show. Open?grails-app/conf/BootStrap.groovy,and then add the following snippet into?init?closure.

? ? ?def init = { servletContext ->
? ? ? ? 1000.times { i ->
? ? ? ? ? ? new Employee(fullname: "Name $i", username: "user$i").save()
? ? ? ? }
? ? ?}

With the above code,we loop 1,000 times to create 1,000 domain objects of class?Employee.

$?grails run-app

and point your browser to?http://localhost:8080/ondemand/employee.zul