Apex Developer Guide

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Apex Developer Guide
Release Notes
Getting Started with Apex
Writing Apex
Running 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 Considerations for Knowledge Articles
Trigger Exceptions
Trigger and Bulk Request Best Practices
Asynchronous Apex
Exposing Apex Methods as SOAP Web Services
Exposing Apex Classes as REST Web Services
Apex Email Service
Using the InboundEmail Object
Visualforce Classes
JavaScript Remoting
Apex in AJAX
Apex Transactions and Governor Limits
Using Salesforce Features with Apex
Integration and Apex Utilities
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

Context Variable Considerations

Be aware of the following considerations for trigger context variables:
  • trigger.new and trigger.old cannot be used in Apex DML operations.
  • You can use an object to change its own field values using trigger.new, but only in before triggers. In all after triggers, trigger.new is not saved, so a runtime exception is thrown.
  • trigger.old is always read-only.
  • You cannot delete trigger.new.

The following table lists considerations about certain actions in different trigger events:

Trigger Event Can change fields using trigger.new Can update original object using an update DML operation Can delete original object using a delete DML operation
before insert Allowed. Not applicable. The original object has not been created; nothing can reference it, so nothing can update it. Not applicable. The original object has not been created; nothing can reference it, so nothing can update it.
after insert Not allowed. A runtime error is thrown, as trigger.new is already saved. Allowed. Allowed, but unnecessary. The object is deleted immediately after being inserted.
before update Allowed. Not allowed. A runtime error is thrown. Not allowed. A runtime error is thrown.
after update Not allowed. A runtime error is thrown, as trigger.new is already saved. Allowed. Even though bad code could cause an infinite recursion doing this incorrectly, the error would be found by the governor limits. Allowed. The updates are saved before the object is deleted, so if the object is undeleted, the updates become visible.
before delete Not allowed. A runtime error is thrown. trigger.new is not available in before delete triggers. Allowed. The updates are saved before the object is deleted, so if the object is undeleted, the updates become visible. Not allowed. A runtime error is thrown. The deletion is already in progress.
after delete Not allowed. A runtime error is thrown. trigger.new is not available in after delete triggers. Not applicable. The object has already been deleted. Not applicable. The object has already been deleted.
after undelete Not allowed. A runtime error is thrown. Allowed. Allowed, but unnecessary. The object is deleted immediately after being inserted.