Question

在activemodel关系上运行reduce时出现一个非常奇怪的错误。这似乎是在呼叫＆＃34; c.name＆＃34;在我的reduce代码中导致错误。 c.name返回字符串＆＃34;俄罗斯联邦＆＃34;。我使用reduce不正确吗？

这是错误：

[2014-03-17T21:12:40.174655 #9240] FATAL -- :
ActiveModel::MissingAttributeError (can't write unknown attribute `Russian Federation'):
app/controllers/registrations_controller.rb:96:in `block in pluck_countries'
app/controllers/registrations_controller.rb:96:in `pluck_countries'

来自控制台的更大堆栈跟踪：

@third_party_countries.reduce(@hsh) {|hsh, c| hsh[c.name] = ThirdPartyShipping.first }
ActiveModel::MissingAttributeError: can't write unknown attribute `Russian Federation'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/attribute_methods/write.rb:47:in `write_attribute'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/attribute_methods/dirty.rb:70:in `write_attribute'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/attribute_methods.rb:341:in `[]='
from (irb):3:in `block in irb_binding'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/relation/delegation.rb:63:in `each'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/relation/delegation.rb:63:in `reduce'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.2/lib/active_record/relation/delegation.rb:63:in `method_missing'
from (irb):3
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/commands/console.rb:90:in `start'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/commands/console.rb:9:in `start'
from /var/www/html/babiators.com/landf/vendor/bundle/ruby/2.0.0/gems/railties-4.0.2/lib/rails/commands.rb:62:in `<top (required)>'
from bin/rails:4:in `require'
from bin/rails:4:in `<main>'

以下是代码：

@third_party_countries = Country.third_party_countries

@hsh = HashWithIndifferentAccess.new
@third_party_countries.reduce(@hsh) {|hsh, c| hsh[c.name] = c.third_party_shipping }

国家架构：

create_table "countries", force: true do |t|
  t.string   "name"
  t.float    "shipping_rate"
  t.integer  "third_party_shipping_id"
  t.datetime "created_at"
  t.datetime "updated_at"
  t.integer  "product_id"
end

国家模式：

class Country < ActiveRecord::Base
  belongs_to :third_party_shipping
  has_and_belongs_to_many :products
  has_many :addresses

  validates_presence_of :name
  validates_uniqueness_of :name

  before_create :init
  after_initialize :init

  scope :shippable, -> { where(third_party_shipping_id: nil) }
  scope :third_party_countries, -> { where.not(third_party_shipping_id: nil) }

  def shipping_price 
    self.shipping_rate * 100
  end

  def free_shipping
    self.shipping_rate <= 0 and self.third_party_shipping_id.nil?
  end

  def paid_shipping
    !self.free_shipping
  end

  def shipping_display
    if self.free_shipping
      "free"
    elsif self.paid_shipping
      self.shipping_rate      
    end
   end

  private
  def init
    if self.shipping_rate.blank? 
      self.shipping_rate = 0
    end
  end
end

Answer 1

由于您在循环之外声明@hsh，因此您无需inject / reduce引入的额外复杂性。只需使用each：

@hsh = HashWithIndifferentAccess.new
@third_party_countries.each{ |c| @hsh[c.name] = c.third_party_shipping }

现有代码的问题在于，使用inject / reduce时，块的返回值将作为第一个参数传递给下一次调用。您需要从块中返回hsh，否则c.third_party_shipping的值将作为hsh传递给下一次调用，并且您有效地执行c.third_party_shipping[c.name]。< / p>

可以通过返回hsh ...

使其正常工作

@third_party_countries.reduce(@hsh) do |hsh, c|
   hsh[c.name] = c.third_party_shipping
   hsh
end

但你不应该。您不需要此功能。 each_with_object是正确的使用方法：

@hsh = @third_party_countries.each_with_object(HashWithIndifferentAccess.new) do |hsh, c|
   hsh[c.name] = c.third_party_shipping
end

您也可以map将数据集合@hsh = HashWithIndifferentAccess[@third_party_countries.map { |c| [c.name, c.third_party_shipping] }]，并使用该数组初始化哈希：

[[a, b], [c, d]]

这依赖于在数组和散列之间自由转换的能力。数组{ a => b, c => d }会转换为哈希{{1}}。

ActiveModel :: MissingAttributeError（不能写未知属性'俄罗斯联邦'）：

1 个答案: