The records that fire the after trigger are read-only
6861
System.FinalException: Record is read-only: Trigger.updateCompetitors: line 24
86693
Trigger to prevent duplication of records in Salesforce
136800
DML statement cannot operate on Trigger.new or Trigger.old
4608
Why can I modify a read-only file?
39314
Parent and children relationships accessible via trigger?
41501
Locking in "Read Committed Snapshot"
123277
execution of BeforeUpdate caused by: System.StringException: Invalid id: in trigger
125805
Not able to catch an exception (Custom + Standard) from trigger
79825
Trigger flow if a specific field on the updated record changed
140004
scenario for recursive trigger
133977
Alter CONSTRAINT or stored procedure only to check when insert not on update
27656
Why I can't read a read only file?
53617
Basic Oracle Trigger audit table
117143
Can a mandatory trigger be missed?
142166
What are the benefits to marking a field as `readonly` in C#?
33613
Why is this trigger finding a null value despite the field being populated?
151899
SQL Server triggers - order of execution