Sorry to drag this up again, but…
I've also come across a use case as I'm migrating data in MySQL. I had to migrate data from a single table to MTI, which meant I had to investigate INFORMATION_SCHEMA, find the relevant constraints and change them in the migration script before I could migrate my data.
I appreciate that migrations and emails/usernames as PKs, are probably the only use cases, and that in general you wouldn't want the onUpdate to cascade... but is there some sort of extension that can update the constraints of all tables referencing the PK of a specified table to allow the onUpdate? If not, is that possible? Perhaps this should be raised against the doctrine migrations project... I'm not sure and would value some steer.
For anyone wondering, here's how I found the relevant constraints to batch update the onUpdate behaviour during migrations in mysql:
SELECT a.CONSTRAINT_SCHEMA, a.CONSTRAINT_NAME, a.TABLE_NAME, a.COLUMN_NAME, a.REFERENCED_TABLE_NAME, a.REFERENCED_COLUMN_NAME, c.UPDATE_RULE, c.DELETE_RULE FROM KEY_COLUMN_USAGE a LEFT JOIN REFERENTIAL_CONSTRAINTS c ON a.CONSTRAINT_NAME = c.CONSTRAINT_NAME AND a.CONSTRAINT_SCHEMA=c.CONSTRAINT_SCHEMA WHERE a.CONSTRAINT_SCHEMA = '<db-name>' AND a.REFERENCED_TABLE_NAME='<table-name>'
Then repeat the following for each constraint whose UPDATE_RULE is RESTRICT:
ALTER TABLE <table-name> DROP FOREIGN KEY `<constraint-name>`
ALTER TABLE <table-name> ADD CONSTRAINT `<constraint-name>` FOREIGN KEY (`<column-name>`) REFERENCES `<referenced-table-name>` (`<referenced-column-name>`) ON UPDATE CASCADE ON DELETE CASCADE");