DataService  - AS3 ADEP Data Services

Package	mx.data
Class	public class DataService
Inheritance	DataService DataManager Object
Subclasses	DataService

A DataService instance is constructed specifying the desired destination. Destinations are generally configured from the services-config.xml file, but can also be configured dynamically with runtime configuration, as in the case of model-driven development.

There are two different sets of methods that retrieve data from the specified remote destination. The first are for collection managed objects. The second are for single managed objects.

For collection managed objects, you use the DataService.fill() method. This method populates an ArrayCollection with objects that this service manages.

To get single manged objects, use the DataService.getItem() and DataService.createItem() methods.

When a previously filled ArrayCollection is no longer needed or the items within that collection should no longer receive or create updates, call the DataService.releaseCollection() method.

When an item previously retrieved using DataService.getItem() or DataService.createItem() is no longer needed or should not receive or create updates, call the DataService.releaseItem() method The DataService.createItem() and DataService.getItem() methods return an ItemReference instance that you can use to release a specific instance of a single managed object. Unlike the DataService.releaseItem() method, calling the ItemReference.releaseItem() method releases a specific instance of a single managed object. The DataService.releaseItem() method releases the first single managed object that it finds with an identity that matches a specified identity. This is fine as long as the number of calls to the DataService.getItem() and DataService.createItem() methods matches the number of calls to the DataService.releaseItem() method.

A connection to the remote destination is created automatically the first time you call any methods that require a connection. For example, when you call the DataService.fill() method or the DataService.commit() method when there are uncommitted updates, the DataService instance attempts to establish a connection to the remote destination. To force a DataService instance to disconnect, call the DataService.disconnect() method. You can use the DataService.disconnect() method to clean up remote destination resources that are no longer needed. Because other services may be using the same physical connection, calling the DataService.disconnect() method may terminate the connection.

The bindable connected property indicates the current state of the associated DataService connection.

If a remote destination has declared any security constraints for an operation, you must provide credentials by calling the DataService.setCredentials() method. A call to the DataService.setCredentials() method turns into a login command at the remote destination. To change credentials or invalidate the current session, call the DataService.logout() method, which releases all local managed data. Calling the DataService.logout() method is equivalent to calling the DataService.release() method.

Each DataService instance has a dataStore property that returns an object of type mx.data.DataStore. This object stores the uncommitted changes for one or more DataService instances. By default, a DataService instance shares the same DataStore instance with other DataService instances if they have managed association properties and share the same set of channels. When sharing a DataStore instance, a call to the commit() method on one DataService instance commits changes for all DataService instances using the shared DataStore instance. This preserves the order of operations in the event that there are dependencies between the changes in the associated DataService instances.

DataService and DataStore instances dispatch result and fault events for all operations that require a remote call.

Note: if you create two DataService instances that point to the same destination, both instances share the same collection of managed objects and dispatch the same set of events. For example, if you add an event listener to one DataService instance for a destination and you use a different instance to initiate an operation, the first DataService instance still receives those events. Each operation you initiate on a DataService instance returns an AsyncToken instance. You can add an event responder to that AsyncToken instance to receive a result event specific to that operation. This approach often produces cleaner code than adding a result or fault event handler globally for a given destination.

You can use data binding on properties of any managed object for a DataService instance. A DataService instance also dispatches a "message" event when a remote operation occurs for any managed object. For example, when a remote process updates a locally managed item, a message is pushed to all DataService instances that are still managing that item. This message is dispatched as a MessageEvent.MESSAGE event.

A conflict event is dispatched when a conflict is detected either at the remote destination in response to a change the DataService instance commits or due to a pushed change that conflicts with a local uncommitted change. You can handle conflict events by listening for DataConflictEvent.CONFLICT. Use data binding to update user interface controls by binding to the DataService.conflicts.resolved property.

The DataService class supports the following data synchronization configuration modes:

• autoCommit - when true each change is immediately sent to the remote destination when detected. When this is false, you must make an explicit call to the commit() method. Use the bindable DataService.commitRequired property determine if there are uncommitted changes.
• autoSyncEnabled - This affects any fill(), getItem() or createItem() method calls and determines whether managed instances listen for changes made to these objects by other clients or by the DataServiceTransaction server push API at the remote destination.
• autoMerge - Controls whether changes received from a remote destination are applied immediately or queued up until a call to the DataService.merge() method is made.

Use the DataService.revertChanges() method to revert changes for a specific item or for all items. When an error occurs for a remote destination operation, the committed changes are put back into the uncommitted queue so the data stays in sync with the data at the remote destination. If the changes are in error, you typically make a call to the DataService.revertChanges() method to undo the changes as part of a fault handler.

The mx.data.mxml.DataService class is an MXML-specific subclass of the mx.data.DataService class that allows binding to the properties of a DataService instance.

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  <mx:DataService
   Properties
   autoCommit="true"
   autoMerge="true"
   autoSaveCache="false"
   autoSyncEnabled="true"
   conflictDetector="No default."
   dataStore="No default."
   destination="No default."
   pageSize="No default."
   id="No default."
 
   Events
   conflict="No default."
   fault="No default."
   message="No default."
   propertyChange="No default."
   result="No default."
 />
 

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