Raised when an error occurred while doing a mass assignment to an attribute through the attributes= method. The exception has an attribute property that is the name of the offending attribute.

Methods
N
Attributes
[R] exception
[R] attribute
Class Public methods
new(message, exception, attribute)

Source: show | on GitHub 

     # File activerecord/lib/active_record/errors.rb, line 166
166:     def initialize(message, exception, attribute)
167:       @exception = exception
168:       @attribute = attribute
169:       @message = message
170:     end