Welcome!

Adobe Flex Authors: Matthew Lobas, PR.com Newswire, Shelly Palmer, Kevin Benedict

Related Topics: Adobe Flex

Adobe Flex: Article

End-to-End Rapid Application Development with Data Services & Adobe Flex

Excerpts from Chapter 6 of Rich Internet Applications With Adobe Flex & Java

The simplest way to explain Flex Data Services (FDS) is to compare them with Flex Remoting. Simply put, FDS addresses only a subset of operations facilitated via Flex Remoting - result set requests. However, whereas Flex Remoting enables one-way requests, FDS combines one-way requests with the publish/subscribe mechanism so that besides the original result set FDS sends the client live updates produced by other clients of the same destination. And there's one more dimension in which Data Services depart from Flex Remoting - support for hierarchical collections, but we won't be covering that subject in this book.

In other words, FDS resolves the task of programming data collaboration: Several users may edit different rows and columns of the "same" DataGrid and see each other's changes automatically pushed by the server. Now, what if they overlap each other's work? In terms of FDS that's called a conflict and the FDS API provides for flexible conflict resolution, which may require the user's intervention.

An FDS destination can be configured for working with the data that is persisted to a data store as well as supporting scenarios that persist the data in the server's memory. To that end, FDS provides Java and ActionScript data adapters that are responsible for reading and updating a persistent data store according to its type. In this chapter we'll focus on use cases involving Java adapters.

Flex Data Services & Automation: Problem Statement & Solution
Robust in enabling collaborative manipulation of data, FDS demands a substantial development effort in case of persistent data stores. In particular, you need to build:

  • A Java Data Access Object class that implements retrieve, update, delete, and insert of the data;
  • Java Data Transfer Objects (DTO);
  • A matching ActionScript data transfer object class;
  • A configuration file, which registers identity columns of the result set and, optionally, argument types for every retrieval method and other parameters.
We just mentioned four classes/files containing hard-coded names of the fields and there are more. To function properly, these hard-coded values have to be kept in sync, which is an additional maintenance effort whenever the data structures change.

Addressing this complexity, the main idea of this chapter is not to cover every twist of the FDS API, but rather automate the development effort that FDS takes for granted. We'll start with a "manual," albeit simplified, example of using DataServices. Then we'll introduce you to the methodology of complete code generation based on the pre-written XSL templates and FDS-friendly XML metadata, which will be extracted from the annotated Java abstract classes.

This methodology is fully implemented in DAOFlex - an Open Source utility that's a complementary addition to this book. We'll gradually introduce this tool by leading you through a process of creating the most comprehensive template that generates a complete DataServices Data Access Object DAO. Finally, we'll show you how to run and customize DAOFlex in your development environment so that writing and synchronizing routine DataServices support classes becomes a task of the Ant building tool and not yours!

A "Manual" FDS Application
Let's handcraft the application presented in Figure 6.1. This application displays a Panel with a scrollable DataGrid that we consciously did not size in the horizontal dimension, so that all columns can be viewed without shrinking. The database result set is ultimately produced by the following SQL query that will use a bound variable in place of the question mark:

    select * from employee where start_date < ?

There are two buttons below the DataGrid: Fill and Commit. As the names imply, these buttons pull the original data from the database table and submit the data changes back to an FDS destination. A separate Parameters panel permits entering parameters of the back-end method behind the Fill button, which, in our case, is the employee start date :

Building the Client Application
Let's build the client application first. The full listing of the application is presented in Listing 6.1. We start with defining the mx:DataServices object (a k a ds), which points to the destination "Employee." Later, when we get to the server components we'll discuss mapping this destination to the backing Java class:

    <mx:DataService id="ds" destination="Employee" fault="onFault(event)" />

We provide only a rudimentary handler of the fault event that's sufficient to keep us aware of any anomalies that may occur along the way. Dynamic referencing fault and faultString properties will spare us from casting to a specific event:

    private function onFault(evt:Event):void {
       Alert.show(evt["fault"]["faultString"], "Fault");
    }

Then we define a handler of the application's onCreationComplete event where we instantiate a collection to be eventually associated with our mx:DataService object and, most importantly, set both autoCommit and autoSyncEnabled of the ds to false:

    private function onCreationComplete() : void {
       collection = new ArrayCollection();
       ds.autoCommit=false;
       ds.autoSyncEnabled=false;
    }

By setting autoCommit to false we state that all updates have to be batched and explicitly submitted to the server as a single transaction during the ds.commit() call. By setting autoSyncEnabled to false we effectively protect our local instance of data from delivery of messages caused by other clients connected to destination "Employee." Setting autoSyncEnabled to false is entirely optional, and we use it to avoid dealing with application specific conflict resolution. In particular, in the handler of the Commit button's click event you might uncomment the first line to support the "optimistic" way of handling the conflicts:

    private function commit_onClick():void {
       //ds.conflicts.acceptAllClient();
       // Optimistic conflict handling, as oppose to
       ds.conflicts.acceptAllServer();
       ds.commit();
    }

Last, we have to initiate the population of the local collection with the ds.fill() method, which we do inside the click event handler of the button Fill:

    private function fill_onClick():void {
       ds.release();
       ds.fill(collection, param_getEmployees_startDate.selectedDate);
    }

The scripting portion of the application is completed so let's build the UI. We create a DataGrid with the dataProvider bound to our collection in Listing 6.1. For brevity's sake, we didn't list all the columns here: you'll have a chance to scrutinize them in the subsequent section of this chapter.

The DataGrid and ControlBar with Fill and Commit buttons are put inside a Panel, with DataGrid's title bearing the name of the destination and a specific getEmployees method of that destination, which will ultimately be invoked during the ds.fill() call. The second panel, titled Parameters, contains a form with a single item mx:DateField. Both panels are embraced by the VDividedBox.

We've included a linkage variable of the data transfer type to ensure that the corresponding ActionScript class (EmployeeDTO) will be linked into the generated SWF file.

<?xml version="1.0" encoding="UTF-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" backgroundColor="#FFFFFF"
creationComplete="onCreationComplete()">
   <mx:DataService id="ds" destination="Employee" fault="onFault(event)" />
   <mx:VDividedBox width="800" height="100%">
    <mx:Panel title="Employee::getEmployees()" width="800" height="70%">
     <mx:DataGrid id="dg" dataProvider="{collection}" editable="true" height="100%">
      <mx:columns><mx:Array>
       <mx:DataGridColumn dataField="EMP_ID" headerText="Emp Id" />
       <mx:DataGridColumn dataField="MANAGER_ID" headerText="Manager Id" />
       <mx:DataGridColumn dataField="EMP_FNAME" headerText="Emp Fname" />
       . . . .
      </mx:Array></mx:columns>
     </mx:DataGrid>
     <mx:ControlBar>
      <mx:Button label="Fill" click="fill_onClick()"/>
      <mx:Button label="Commit" click="commit_onClick()"        enabled="{ds.commitRequired}"/>
     </mx:ControlBar>
    </mx:Panel>
    <mx:Panel title="Parameters" width="100%" height="30%">
     <mx:HBox height="100%" width="100%">
      <mx:Form label="getEmployees()">
       <mx:FormItem label="startDate:">
        <mx:DateField id="param_getEmployees_startDate" selectedDate="{new Date()}"/>
       </mx:FormItem>
      </mx:Form>
     </mx:HBox>
   </mx:Panel>
</mx:VDividedBox>
<mx:Script>
   <![CDATA[
   import mx.controls.Alert;
   import mx.collections.ArrayCollection;
   import com.theriabook.datasource.dto.EmployeeDTO;
   private var linkage:com.theriabook.datasource.dto.EmployeeDTO = null;
   [Bindable]
   private var collection : ArrayCollection;
   private function fill_onClick():void {
     ds.release();
     ds.fill(collection, param_getEmployees_startDate.selectedDate);
   }
   private function onCreationComplete() : void {
     collection = new ArrayCollection();
     ds.autoCommit=false;
     ds.autoSyncEnabled=false;
   }
   private function commit_onClick():void {
     ds.conflicts.acceptAllClient();
     ds.commit();
   }
   private function onFault(evt:Event):void {
     Alert.show(evt["fault"]["faultString"], "Fault");
   }

   ]]>
</mx:Script>
</mx:Application>


More Stories By Victor Rasputnis

Dr. Victor Rasputnis is a Managing Principal of Farata Systems. He's responsible for providing architectural design, implementation management and mentoring to companies migrating to XML Internet technologies. He holds a PhD in computer science from the Moscow Institute of Robotics. You can reach him at [email protected]

More Stories By Yakov Fain

Yakov Fain is a Java Champion and a co-founder of the IT consultancy Farata Systems and the product company SuranceBay. He wrote a thousand blogs (http://yakovfain.com) and several books about software development. Yakov authored and co-authored such books as "Angular 2 Development with TypeScript", "Java 24-Hour Trainer", and "Enterprise Web Development". His Twitter tag is @yfain

More Stories By Anatole Tartakovsky

Anatole Tartakovsky is a Managing Principal of Farata Systems. He's responsible for creation of frameworks and reusable components. Anatole authored number of books and articles on AJAX, XML, Internet and client-server technologies. He holds an MS in mathematics. You can reach him at [email protected]

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


IoT & Smart Cities Stories
Dion Hinchcliffe is an internationally recognized digital expert, bestselling book author, frequent keynote speaker, analyst, futurist, and transformation expert based in Washington, DC. He is currently Chief Strategy Officer at the industry-leading digital strategy and online community solutions firm, 7Summits.
Digital Transformation is much more than a buzzword. The radical shift to digital mechanisms for almost every process is evident across all industries and verticals. This is often especially true in financial services, where the legacy environment is many times unable to keep up with the rapidly shifting demands of the consumer. The constant pressure to provide complete, omnichannel delivery of customer-facing solutions to meet both regulatory and customer demands is putting enormous pressure on...
IoT is rapidly becoming mainstream as more and more investments are made into the platforms and technology. As this movement continues to expand and gain momentum it creates a massive wall of noise that can be difficult to sift through. Unfortunately, this inevitably makes IoT less approachable for people to get started with and can hamper efforts to integrate this key technology into your own portfolio. There are so many connected products already in place today with many hundreds more on the h...
The standardization of container runtimes and images has sparked the creation of an almost overwhelming number of new open source projects that build on and otherwise work with these specifications. Of course, there's Kubernetes, which orchestrates and manages collections of containers. It was one of the first and best-known examples of projects that make containers truly useful for production use. However, more recently, the container ecosystem has truly exploded. A service mesh like Istio addr...
Digital Transformation: Preparing Cloud & IoT Security for the Age of Artificial Intelligence. As automation and artificial intelligence (AI) power solution development and delivery, many businesses need to build backend cloud capabilities. Well-poised organizations, marketing smart devices with AI and BlockChain capabilities prepare to refine compliance and regulatory capabilities in 2018. Volumes of health, financial, technical and privacy data, along with tightening compliance requirements by...
Charles Araujo is an industry analyst, internationally recognized authority on the Digital Enterprise and author of The Quantum Age of IT: Why Everything You Know About IT is About to Change. As Principal Analyst with Intellyx, he writes, speaks and advises organizations on how to navigate through this time of disruption. He is also the founder of The Institute for Digital Transformation and a sought after keynote speaker. He has been a regular contributor to both InformationWeek and CIO Insight...
Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settlement products to hedge funds and investment banks. After, he co-founded a revenue cycle management company where he learned about Bitcoin and eventually Ethereal. Andrew's role at ConsenSys Enterprise is a mul...
To Really Work for Enterprises, MultiCloud Adoption Requires Far Better and Inclusive Cloud Monitoring and Cost Management … But How? Overwhelmingly, even as enterprises have adopted cloud computing and are expanding to multi-cloud computing, IT leaders remain concerned about how to monitor, manage and control costs across hybrid and multi-cloud deployments. It’s clear that traditional IT monitoring and management approaches, designed after all for on-premises data centers, are falling short in ...
In his general session at 19th Cloud Expo, Manish Dixit, VP of Product and Engineering at Dice, discussed how Dice leverages data insights and tools to help both tech professionals and recruiters better understand how skills relate to each other and which skills are in high demand using interactive visualizations and salary indicator tools to maximize earning potential. Manish Dixit is VP of Product and Engineering at Dice. As the leader of the Product, Engineering and Data Sciences team at D...
Dynatrace is an application performance management software company with products for the information technology departments and digital business owners of medium and large businesses. Building the Future of Monitoring with Artificial Intelligence. Today we can collect lots and lots of performance data. We build beautiful dashboards and even have fancy query languages to access and transform the data. Still performance data is a secret language only a couple of people understand. The more busine...