紅寶石在Rails3中：錯誤：無法大規模指派保護的屬性：名稱，位置

我有ROR一個問題：紅寶石在Rails3中：錯誤：無法大規模指派保護的屬性：名稱，位置

我想創造一個名爲「類別2」的模式，我用下面的命令：

rails g model category2

然後，我改變了文件* DB /遷移/ 20120521113409_create_category2s.rb *到：

class CreateCategory2s < ActiveRecord::Migration

def change
create_table :category2s do |t| 

    t.string :name 

    t.integer :position 

    t.timestamps 

end 
add_column :events, :category2_id, :integer
add_index :events, :category2_id
end

end

然後，

bundle exec rake db:migrate

當我打開控制檯，輸入

b = Category2.new(:name => 'Ruby', :position => 1)

它返回一個錯誤：

irb(main):009:0> b = Category2.new(:name => 'Ruby', :position => 1)

ActiveModel::MassAssignmentSecurity::Error: Can't mass-assign protected attributes: name, position 

from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.3/lib/active_model/mass_assignment_security/sanitizer.rb:48:in `process_removed_attributes' 

from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.3/lib/active_model/mass_assignment_security/sanitizer.rb:20:in `debug_protected_attribute_removal' 

from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.3/lib/active_model/mass_assignment_security/sanitizer.rb:12:in `sanitize' 

from /usr/local/lib/ruby/gems/1.9.1/gems/activemodel-3.2.3/lib/active_model/mass_assignment_security.rb:230:in `sanitize_for_mass_assignment' 

from /usr/local/lib/ruby/gems/1.9.1/gems/activerecord-3.2.3/lib/active_record/attribute_assignment.rb:75:in `assign_attributes' 

from /usr/local/lib/ruby/gems/1.9.1/gems/activerecord-3.2.3/lib/active_record/base.rb:498:in `initialize' 

from (irb):9:in `new' 

from (irb):9 

from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.3/lib/rails/commands/console.rb:47:in `start' 

from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.3/lib/rails/commands/console.rb:8:in `start' 

from /usr/local/lib/ruby/gems/1.9.1/gems/railties-3.2.3/lib/rails/commands.rb:41:in `<top (required)>' 

from script/rails:6:in `require' 

from script/rails:6:in `<main>'

這意味着什麼？

如果我不加參數，我只是喜歡輸入：