Rails中验证
1. validates_presence_of
validates_presence_of()方法是一个标准的Rails验证器，它会检查指定字段存在、并且值不为空。
用法，例如:(C:\Users\Tony\Desktop\rails\deopt\app\models\product.rb)

class Product < ActiveRecord::Base  validates_presence_of :title, :description, :image_urlend   

2. validates_numericality_of
来检查价格是否是合法的数值。

3. validate(只定义验证)
例如:

class Product < ActiveRecord::Base  validates_presence_of :title, :description, :image_url  validates_numericality_of :price  validate :price_must_be_at_least_a_cent  protected  def price_must_be_at_least_a_cent    errors.add(:price, 'should be at least 0.01' ) if price.nil? || price < 0.01  endend   

4. validates_uniqueness_of
确保数据的唯一性:

  validates_uniqueness_of :title

5. validates_format_of
validates_format_of()验证格式是否正确:

  validates_format_of :image_url,                   :with => %r{\.(gif|jpg|png)$}i,                   :message => 'must be a URL for GIF, JPG or PNG image.'