I have a custom page which has a has_many relationship to a dataobject.
These objects are displayed in a getCMSFields HasManyComplexTableField.
I am running a function within onBeforeWrite() in the dataobject's class in order to validate a value which is entered before saving it to the DB. However if the value is not valid I have no way to notify the user. If I attempt to return any value from the onBeforeWrite function then it just hangs with the "saving..." button spinning.
How can I send a meaningful response back to the user?