Raised when a primary key is needed, but not specified in the schema or model.

Methods
N
Attributes
[R] model
Class Public methods
new(model = nil, description = nil)

Source: show | on GitHub 

# File activerecord/lib/active_record/errors.rb, line 283
def initialize(model = nil, description = nil)
  if model
    message = "Unknown primary key for table #{model.table_name} in model #{model}."
    message += "\n#{description}" if description
    @model = model
    super(message)
  else
    super("Unknown primary key.")
  end
end