The way that Flex works with data sources and data is different from other web application environments, such as JSP, ASP, and ColdFusion. Data access in Flex applications also differs significantly from data access in applications that are created in Flash Professional.

Client-side processing and server-side processing

Unlike a set of HTML templates created using JSPs and servlets, ASP, or CFML, the files in a Flex application are compiled into a binary SWF file that is sent to the client. When a Flex application makes a request to an external service, the SWF file is not recompiled and no page refresh is required.

The following example shows MXML code for calling a web service. When a user clicks the Button control, client-side code calls the web service, and result data is returned into the binary SWF file without a page refresh. The result data is then available to use as dynamic content within the application.

<?xml version="1.0"?>
<!-- ds\rpc\RPCIntroExample2.mxml --> 
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml">
    <!-- Declare a WebService component (the specified WSDL URL is not functional). --> 
    <mx:WebService id="WeatherService"
        destination="wsDest"/>

    <mx:Button label="Get Weather" 
        click="WeatherService.GetWeather(input.text);"/>
        
    <mx:TextInput id="input"/>  
</mx:Application>

The following example shows JSP code for calling a web service using a JSP custom tag. When a user requests this JSP, the web service request is made on the server instead of on the client, and the result is used to generate content in the HTML page. The application server regenerates the entire HTML page before sending it back to the browser.

<%@ taglib prefix="web" uri="webservicetag" %>

<% String str1="BRL";
String str2="USD";%>

<!-- Call the web service. -->
<web:invoke
    url="http://www.itfinity.net:8008/soap/exrates/default.asp"
    namespace="http://www.itfinity.net/soap/exrates/exrates.xsd"
    operation="GetRate"
    resulttype="double"
    result="myresult">
    <web:param name="fromCurr" value="<%=str1%>"/>
    <web:param name="ToCurr" value="<%=str2%>"/>
</web:invoke>

<!-- Display the web service result. -->
<%= pageContext.getAttribute("myresult") %>

Data source access

Another difference between Flex and other web application technologies is that you never communicate directly with a data source in Flex. You use a Flex service component to connect to a server-side service that interacts with the data source.

The following example shows one way to access a data source directly in a ColdFusion page:

<CFQUERY DATASOURCE="Dsn"
    NAME="myQuery">
    SELECT * FROM table
</CFQUERY>

To get similar functionality in Flex, use an HTTPService, a WebService, or a RemoteObject component to call a server-side object that returns results from a data source.