错误(私有方法"选择"调用 nil：NilClass)：

Question

为什么我会遇到此错误？我该如何修复？

ActionView :: Template ::错误（私有方法``select'' nil：nilclass）：

class MyformObject
  include ActiveModel::Model
  #validations

@form_structure =
  [
    {  name: :country, model: :car, field_type: :string },
    {  name: :street, model: :repair_center, field_type: :string }
  ]
  def get_model_from_name(name)
    model = @form_structure.select { |record| record[:name] == name }.first[:model]
  end  
  def type_for_attribute(name)
    get_model_from_name(name).to_s.capitalize.constantize.type_for_attribute
  end 
  def has_attribute?(name)
    get_model_from_name(name).to_s.capitalize.constantize.attributes.key?(name.to_s)
   end
def self.fields_of_model(model)
  form_structure.select { |record| record[:model] == model }.map { |record| record[:name] }
end
 end

更新版本：

错误：未定义的方法`[] nil：nilclass def get_model_from_name（name）
model = self.class.form_structure.select {|记录|记录[：name] ==名称} .first [：model] 结束

class MyformObject
  include ActiveModel::Model
  #validations

def self.form_structure 
  [
    {  name: :country, model: :car, field_type: :string },
    {  name: :street, model: :repair_center, field_type: :string }
  ]
end
  def get_model_from_name(name)
    model = self.class.form_structure.select { |record| record[:name] == name }.first[:model]
  end  
  def type_for_attribute(name)
    get_model_from_name(name).to_s.capitalize.constantize.type_for_attribute
  end 
  def has_attribute?(name)
    get_model_from_name(name).to_s.capitalize.constantize.attributes.key?(name.to_s)
   end
def self.fields_of_model(model)
  form_structure.select { |record| record[:model] == model }.map { |record| record[:name] }
end
def self.delegate_fields_to(*models)
      models.each do |model|
        fields_of_model(model).each do |attr|
          delegate attr.to_sym, "#{attr}=".to_sym, to: model
        end
      end
    end
 end

Answer 1

imho，常数是处理该数组的好方法，并充满了硬编码值，仅包含两个元素。

因此，您可以做类似：

的事情

class MyformObject
  FORM_STRUCTURE = [
    { name: :country, model: :car, field_type: :string },
    { nname: :street, model: :repair_center, field_type: :string }
  ].freeze
  private_constant :FORM_STRUCTURE
  def get_model_from_name(name)
    FORM_STRUCTURE.select { |record| record[:name] == name }.first[:name]
  end 
end
p MyformObject.new.get_model_from_name(:country)
# [:country]

在那里您可以看到常数无法修改，并且仅在MyFormObject范围内使用。

我删除了模型本地变量分配，因为它没有使用。

Answer 2

您可以尝试这样的尝试使执行一点轻松执行，

  def get_model_from_name(name)
    model = form_structure.select { |record| record[:name] == name }.first[:model]
  end
  def form_structure
    [
      {  name: :country, model: :car, field_type: :string },
      {  name: :street, model: :repair_center, field_type: :string }
    ]
  end

为了更好的封装，您可以将方法form_structure放在私有范围中。