Why will extra fields in my Rails form not save to the database table?

I have my form

<% form_tag users_path, :id => 'registrationForm'开发者_JS百科 do %>
  <div class="formElement">
    <label for="emailAddress">Email Address</label>
    <input name="user[email]" type="text">
  </div>
  <div class="formElement">
    <label for="password">Password</label>
    <input id="password" name="user[password]" type="password">
  </div>
  <div class="formElement">
    <label for="passwordConfirmation">Re-Enter Password</label>
    <input id="passwordConfirmation" name="user[password_confirmation]" type="password">
  </div>

  <div class="formElement right">
    <input name="commit" value="Create" type="submit">
  </div>
<% end %>

and then my controller method to process this which contains

@user = User.new(params[:user])
@user.save do |result|
  ...
end

This works fine. However, if I add 'first_name' and 'last_name' fields to my database table and add

<div class="formElement">
  <label for="firstName">First Name</label>
  <input id="firstName" name="user[first_name]" type="text" />
</div>
<div class="formElement">
  <label for="lastName">Last Name</label>
  <input id="lastName" name="user[last_name]" type="text" />
</div>

to my form, I get

Mysql::Error: Column 'last_name' cannot be null: INSERT INTO users (salt, ship_address_id, created_at, single_access_token, last_request_at, bill_address_id, crypted_password, remember_token_expires_at, updated_at, perishable_token, api_key, failed_login_count, current_login_ip, openid_identifier, current_login_at, last_name, remember_token, persistence_token, login_count, last_login_ip, last_login_at, login, email, first_name) VALUES('gPa4FNsPHbfxLz1FTZJ8', NULL, '2010-11-03 18:07:24', 'INl0QTDduoCKSdLLXEqb', '2010-11-03 18:07:24', NULL, '900d7300768651e4814ca16b1dd39b85e8111c92a63d366c82e3f1d501dc7b85efc060bc2032e55e4405fe33b0883b0ad586fe47e99261b046a34a8b9d785333', NULL, '2010-11-03 18:07:24', 'r8YSPUfKsmbIIJryvz5C', NULL, 0, '127.0.0.1', NULL, '2010-11-03 18:07:24', NULL, NULL, 'd4fe33e9c1bde5e2468d74d3dc1de28089f565d7e0d39584690452547be6d3bbf529e9ac118575529f34e377cce315697538c64b19f799e386d6977a8f37912e', 1, NULL, NULL, 'testuser3@test.com', 'testuser3@test.com', NULL)

Here's the parameters the error page says were passed:

{"commit"=>"Create", "authenticity_token"=>"tFpn+DGMU3VfeaSrc5ckVoVCxfy76Xm0Mqf8Jx8JEFs=", "user"=>{"password_confirmation"=>"test", "last_name"=>"User3", "password"=>"test", "first_name"=>"Test3", "email"=>"testuser3@test.com"}}

Any ideas why I get this MySQL error?

---

Are you using attr_accessible or attr_protected in your User model to guard against mass-assignment exploits?