Why does scaffold ignores some fields?

Hello,

somehow the 'scaffold' method does not emits HTML fields for all the fields of my models. For example, this simple controller:

  class CatalogController < ApplicationController     scaffold :fact   end

and a model backed by (sqlite3, tested also with mysql)

  create table "facts" (     "id" integer primary key autoincrement,     "type" varchar not null,     "device_id" integer not null,     "stated_on" date not null,     "created_at" datetime not null,     "updated_at" datetime not null,     "approved" boolean default false   );

produces HTML fields only for "Stated on", "Created at", "Updated at" and "Approved". "type" and "device_id" are ignored. Why?