我们希望我们的注册表单对象具有与任何其他ActiveRecord模型相同的API：

// view.html
<%= form_for(@book) do |f| %>
<% end %>

# controller.rb
def create
  @book = Book.new(book_params)

  if @book.save
    redirect_to @book,notice: 'Book was successfully created.'
  else
    render :new
  end
end

为此,我们创建以下对象：

class RegForm
  include ActiveModel::Model

  attr_accessor :company_name,:password

  def save
    # Save Location and Account here
  end
end

现在,通过包含ActiveModel :: Model,我们的RegForm获得了大量功能,包括显示错误和验证属性(是的,不必包含ActiveModel :: Validations).在下一步中,我们添加一些验证：

validates :email,:password,presence: true

我们更改保存,以便它运行这些验证：

def save
  validate
  # Save Location and Account here
end

如果所有验证都通过,则validate返回true,否则返回false.

validate还向@reg_form添加了errors(所有ActiveRecord模型都有一个错误哈希值,当验证失败时填充该哈希值).这意味着在视图中我们可以执行以下任何操作：

@reg_form.errors.messages
#=> { email: ["can't be blank"],password: ["can't be blank"] }

@reg_form.errors.full_messages
#=> ["Email can't be blank","Password can't be blank"]

@reg_form.errors[:email]
#=> ["can't be blank"]

@reg_form.errors.full_messages_for(:email)
#=> ["Email can't be blank"]

同时,我们的RegistrationsController看起来应该是这样的：

def create
  @reg_form = RegForm.new(reg_params)

  if @reg_form.save
    redirect_to @reg_form,notice: 'Registration was successful'
  else
    render :new
  end
end

我们可以清楚地看到,当@ reg_form.save返回false时,将重新呈现新视图.

最后,我们更改保存,以便我们的模型保存调用包含在transaction中：

def save
  if valid?
    ActiveRecord::Base.transaction do
      location = Location.create!(location_params)
      account = location.create_account!(account_params)
    end
    true
  end
rescue ActiveRecord::StatementInvalid => e
  # Handle database exceptions not covered by validations.
  # e.message and e.cause.message can help you figure out what happened
end

值得注意的要点：

>创造！用来代替创建.如果引发异常(通常会发生爆炸的方法),则仅回滚transaction.
> validate is just an alias for valid?.为避免所有缩进,我们可以在save方法的顶部使用guard：

return if invalid?

>我们可以通过执行以下操作将数据库异常(like an email uniqueness constraint)转换为错误：

rescue ActiveRecord::RecordNotUnique
  errors.add(:email,:taken)
end

>我们可以使用符号:base添加与属性无直接关联的错误：

errors.add(:base,'Company and Email do not match')