Chatter data Model and objects.

Hai friends , i have explored on the chatter,especially on chatter data model and displaying chatter feeds on Vfpage ,sending comments to feeds from Vfpage.
first i will explain about the chatter objects and chatter data model.
              Feed item is the Basic entity in the chatter,information about the each chatter feed(post) like created date,created by,body,....are stored as Feed item in chatter.Here Feed items are different types  ,they are 
                                   User Profile feed
                                   Entity feed
                                   News Feed
                                   Collaboration Group Feed.
Entity Feed :- In Chatter to follow data ,we need  to enable feed tracking for the desired object and we can specify the fields to know updations for that fields.
 Set up--> App Setup--> customize-->Chatter-->Enable feed tracking.
There you can select object and fields also.(Note you can follow only 20 fields for an object.)
Let us consider you have selected Account object,then entity feeds for that object are stored in Accountfeed(chatter automatically created this).if you want to see all the feeds related to account object you can query data from that records,


Example:-
SELECT Body, Type, Title, CreatedBy.Name

 FROM AccountFeed WHERE ParentId = <Account Record Id>

 in the case of custom object

SELECT Body, Type, Title, CreatedBy.Name

 FROM Employee__Feed WHERE ParentId = < Employee Record Id>

   When you update the record then the updates are stored in to FeedTrackedChanges.this contains both  old and new value of the field for a particular record.We can not query directly from Feed tracked changes,

you can query like,


Example:-

  SELECT Id, (SELECT Id, FieldName, OldValue, NewValue FROM                        
  FeedTrackedChanges ) FROM AccountFeed.                     

NewsFeed:-  Newsfeed forms a sort of aggregate of posts of all users, groups, objects that a particular user following. Which hold all the posts, you can see on user home tab.


Example:-

   SELECT Id, Type, Body, Title, CreatedBy.Name FROM Newsfeed


User Profile feed:-User Profile feed like Newsfeed but it is specific to a particular user.
Example:-

  SELECT Id, Type, Body, Title, CreatedBy.Name FROM UserProfileFeed WITH UserId = <User Id>     

 Collaboration Group feed:- It represents chatter feed for a specific chatter group (private/public).
Example:-

SELECT Id, Type, Body, CreatedBy.Name FROM CollaborationGroupFeed where parentId = <GroupId>

Feed Comment:-

If one user adds a comment to another user post, then a record is created in Feed Comment with reference to feeditemid. We can’t directly query the Feed Comment object, we query from Entity feed.

Example:-

 SELECT Id, (SELECT Id, CommentBody, CreatedDate, CreatedById,

 CreatedBy.FirstName, CreatedBy.LastName

 FROM FeedComments ORDER BY CreatedDate DESC LIMIT 10) 

FROM AccountFeed ORDER BY CreatedDate DESC, Id DESC LIMIT 1

                                                                   chatter Data Model