验证Ruby on Rails中has_many项的数量

Question

用户可以将标签添加到代码段:

class Snippet < ActiveRecord::Base

  # Relationships
  has_many :taggings
  has_many :tags, :through => :taggings
  belongs_to :closing_reason

end

我想验证标签的数量:至少为1,最多为6.我如何做到这一点？谢谢.

Answer 1

您始终可以创建自定义验证.

就像是

  validate :validate_tags

  def validate_tags
    errors.add(:tags, "too much") if tags.size > 5
  end

Answer 2

@SooDesuNe在此SO帖子上提供了更好的解决方案

validates :tags, length: { minimum: 1, maximum: 6 }

Answer 3

我认为你可以使用验证.reject(&:marked_for_destruction?).length.

这个怎么样？

class User < ActiveRecord::Base
  has_many :groups do
    def length
      reject(&:marked_for_destruction?).length
    end
  end
  accepts_nested_attributes_for :groups, allow_destroy: true
  validates :groups, length: { maximum: 5 }
end

或这个.

class User < ActiveRecord::Base
  has_many :groups
  accepts_nested_attributes_for :groups, allow_destroy: true
  GROUPS_MAX_LENGTH = 5
  validate legth_of_groups

  def length_of_groups
    groups_length = 0
    if groups.exists?
      groups_length = groups.reject(&:marked_for_destruction?).length
    end
    errors.add(:groups, 'too many') if groups_length > GROUPS_MAX_LENGTH
  end
end

然后,你可以命令.

@user.assign_attributes(params[:user])
@user.valid?

谢谢你的阅读.

参考文献:

http://homeonrails.com/2012/10/validating-nested-associations-in-rails/ http://qiita.com/asukiaaa/items/4797ce44c3ba7bd7a51f