Dec 27, 2012

Streaming APIs - Easy Code


Streaming API is useful when you want notifications to be pushed from the server to the client based on criteria that you define.

The sequence of events when using Streaming API is as follows: (explained in detail later)
1. Create a PushTopic based on a SOQL query. This defines the channel.
2. Clients subscribe to the channel.
3. A record is created or updated (an event occurs). The changes to that record are evaluated.
4. If the record changes match the criteria of the PushTopic query, a notification is generated by the server and received by the subscribed clients.

Before we get started, I recommend you to go through these topics:

1) Push Technology
2) Bayeux Protocol, CometD, and Long Polling


We will achieve this once we are done with all steps (given below):





Now follow these steps:

Prerequisites:
1) The “Streaming API” permission must be enabled -> "Your Name > Setup > Customize > User Interface"
2) The logged-in user must have “Read” permission on the PushTopic standard object to receive notifications.
3) The logged-in user must have “Create” permission on the PushTopic standard object to create and manage PushTopic records.
4) The logged-in user must have “Author Apex” permissions to create a PushTopic by using the Developer Console.


Step 1: Create an Object - In our case we will use Account

Step 2: Create a PushTopic
Use the Developer Console to create the PushTopic record. You can use either Developer Console or Workbench. If needed these records can be updated.

"Your Name > Developer Console"


PushTopic pushTopic = new PushTopic();
pushTopic.Name = 'RefreshAccounts';
pushTopic.Query = 'SELECT Id, Name FROM Account';
pushTopic.ApiVersion = 26.0;
pushTopic.NotifyForOperations = 'All';
pushTopic.NotifyForFields = 'Referenced';
insert pushTopic;


Step 3: Create Static resource

1. Download the CometD compressed archive (.tgz) file from http://download.cometd.org/cometd-2.2.0-distribution.tar.gz
2. Extract the following JavaScript files from cometd-2.2.0-distribution.tar.gz:
• cometd-2.2.0/cometd-javascript/common/target/org/cometd.js
• cometd-2.2.0/cometd-javascript/jquery/src/main/webapp/jquery/jquery-1.5.1.js
• cometd-2.2.0/cometd-javascript/jquery/src/main/webapp/jquery/json2.js
• cometd-2.2.0/cometd-javascript/jquery/src/main/webapp/jquery/jquery.cometd.js


File Name
Static Resource Name
cometd.js
Cometd
jquery-1.5.1.js
Jquery
json2.js
json2
jquery.cometd.js
jquery_cometd




Step 4: Test the PushTopic Channel

Here is the code sample

Visualforce Page


<apex:page id="PG" controller="StreamingAPIController">
<apex:form id="FRM">

    <apex:includeScript value="{!$Resource.cometd}"/>
    <apex:includeScript value="{!$Resource.jquery}"/>
    <apex:includeScript value="{!$Resource.json2}"/>
    <apex:includeScript value="{!$Resource.jquery_cometd}"/>

    <apex:actionFunction name="GetRefreshedAccounts" reRender="PB,PBT"/>

    <script type="text/javascript">
        (function($)
        {
            $(document).ready(function() {
                
                // Connect to the CometD endpoint
                $.cometd.init({
                    url: window.location.protocol+'//'+window.location.hostname+'/cometd/24.0/',
                    requestHeaders: { Authorization: 'OAuth {!$Api.Session_ID}'}
                });
                
                // Subscribe to a topic. JSON-encoded update will be returned in the callback
                // In this example we are using this only to track the generated event
                $.cometd.subscribe('/topic/RefreshAccounts', function(message)
                {
                    //You can use message as it will return you many attributes
                    //I am just using to track that event is generated
                    GetRefreshedAccounts();
                });

            });
        })(jQuery)
    </script>

    <apex:pageBlock id="PB">
        <apex:variable var="count" value="{!0}" />
        <apex:pageBlockTable id="PBT" value="{!getRefreshedAccount}" var="AllAcc">
            
            <apex:column headerValue="S.No.">
                <apex:variable var="count" value="{!count+1}" />
                {!count}
            </apex:column>
            <apex:column value="{!AllAcc.Name}" headerValue="Name"/>
            
        </apex:pageBlockTable>
    </apex:pageBlock>

</apex:form>
</apex:page>

Apex Class


public class StreamingAPIController
{
    //Everytime page is reRendered it will get refreshed values of account
    public List<Account> getRefreshedAccount
    {
        get
        {
            return [select Id, Name from Account LIMIT 50000] ;
        }
        set;
    }
    
    public StreamingAPIController()
    {
    }
}


This is very small and simple sample code, you can do a lot more with streaming APIs. Please refer these documents to learn more:

1) http://www.salesforce.com/us/developer/docs/api_streaming/api_streaming.pdf
2) http://www.salesforce.com/us/developer/docs/api_streaming/index.htm
3)http://wiki.developerforce.com/page/Getting_Started_with_the_Force.com_Streaming_API

6 comments:

  1. Hi, I am trying to do the same thing for attachment object.But unable to do so, as its give an error while i am inserting a record in push object that attachment object is not supported. Is this a limit to streaming API.

    ReplyDelete
  2. Hi.. Good Blog on Streaming API. I have a small question: Can i decide on to which user the Push Notification to occur?
    So for example: If an account record is being updated, and i have Users A,B and C enabled for Streaming API, I want that only User A to be notified about this update.? Internally Salesforce Broadcast this message to all users(using Streaming API) and creating alot of traffic if number of users are high.

    Please help

    Regards,
    Sagar

    ReplyDelete
    Replies
    1. I have never done this.. but I think you can probably control that within your SOQL query, when creating the PushTopic.

      Regards,
      Nash

      Delete
  3. Hi, Excellent blog. The code works fine in a visual force page, but it does not work in visual force TAB. Do I need to make some specific changes to make it work in visual force TAB.

    ReplyDelete
  4. geting Dojo not defined and org not defined when trying to implement the same.
    seems we need to add more header files here. Can anyone help me out with the references.

    Thanks in Advance

    ReplyDelete
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