Force.com Apex Code Developer's Guide

Getting Started
Writing Apex
Ways to Invoke Apex
Invoking Apex
Anonymous Blocks
Triggers
Bulk Triggers
Trigger Syntax
Trigger Context Variables
Context Variable Considerations
Common Bulk Trigger Idioms
Defining Triggers
Triggers and Merge Statements
Triggers and Recovered Records
Triggers and Order of Execution
Operations That Don't Invoke Triggers
Entity and Field Considerations in Triggers
Triggers for Chatter Objects
Trigger Exceptions
Trigger and Bulk Request Best Practices
Asynchronous Apex
Web Services
Apex Email Service
Visualforce Classes
Invoking Apex Using JavaScript
Apex Transactions and Governor Limits
Using Salesforce Features with Apex
Integration and Apex Utilities
Finishing Touches
Reference
Appendices
Glossary
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Triggers for Chatter Objects

You can write triggers on the FeedItem and FeedComment triggers.
  • Only FeedItems of Type TextPost, LinkPost, HasLink, ContentPost, and HasContent can be inserted, and therefore invoke the before or after insert trigger. User status updates don't cause the FeedItem triggers to fire.
  • While FeedPost objects were supported for API versions 18.0, 19.0, and 20.0, don't use any insert or delete triggers saved against versions before 21.0.
  • For FeedItem the following fields are not available in the before insert trigger:
    • ContentSize
    • ContentType

    In addition, the ContentData field is not available in any delete trigger.

  • Triggers on FeedItem objects run before their attachment and capabilities information is saved, which means that ConnectApi.FeedItem.attachment information and ConnectApi.FeedElement.capabilities information may not be available in the trigger.

    The attachment and capabilities information may not be available from these methods: ConnectApi.ChatterFeeds.getFeedItem, ConnectApi.ChatterFeeds.getFeedElement, ConnectApi.ChatterFeeds.getFeedPoll, ConnectApi.ChatterFeeds.getFeedElementPoll, ConnectApi.ChatterFeeds.postFeedItem, ConnectApi.ChatterFeeds.postFeedElement, ConnectApi.ChatterFeeds.shareFeedItem, ConnectApi.ChatterFeeds.shareFeedElement, ConnectApi.ChatterFeeds.voteOnFeedPoll, and ConnectApi.ChatterFeeds.voteOnFeedElementPoll

  • For FeedComment before insert and after insert triggers, the fields of a ContentVersion associated with the FeedComment (obtained through FeedComment.RelatedRecordId) are not available.
  • Apex code uses extra security when executing in a Chatter context. To post to a private group, the user running the code must be a member of that group. If the running user isn't a member, you can set the CreatedById field to be a member of the group in the FeedItem record.
Note the following for the CollaborationGroup and CollaborationGroupMember objects:
  • When CollaborationGroupMember is updated, CollaborationGroup is automatically updated as well to ensure that the member count is correct. As a result, when CollaborationGroupMember update or delete triggers run, CollaborationGroup update triggers run as well.