如何在 Rails 模型类上正确格式化实例变量

Question

我有一个表 Materials，has_one 与 MaterialCosts 相关，has_one 与 MaterialCharges 相关。它们都属于材料，在材料中删除或记录时应dependent: :destroy。

我不确定如何构建 Material 类。必须使用来自每个 Material 实例的两个属性来计算 MaterialCosts 和 MaterialCharges 中的字段。它们是cost_per_sqm 和ink_per_sqm。 factor 是 Material 中的一个字段，也用于 MaterialCharges。为了将实例变量用于创建方法，我是否需要在 Material 中初始化它们？还是只需要attr_accessor？

我知道代码需要重构，但当我尝试播种数据时也出现此错误：

NoMethodError: undefined method `[]' for nil:NilClass on line 26 seeds.rb

第 26 行种子.rb：

Material.create({ product_name: "Novajet Art 255gsm", guk_name: "none", roll_width_in: 44, roll_length_m: 30, factor: 7, rounded_sale_price: 71, list_price: 240.00, cost_per_sqm: 7.16, ink_per_sqm: 3, supplier_discount: 0, sell_per_sqm: 71.11 })

这是我的代码：

  class Material < ApplicationRecord

  has_and_belongs_to_many :job_entries
  has_one :material_cost,  dependent: :destroy
  has_one :material_charge, dependent:  :destroy

  attr_accessor :cost_per_sqm, :ink_per_sqm, :factor

  def initialize(options)
    @cost_per_sqm = options['cost_per_sqm'].to_f
    @ink_per_sqm = options['ink_per_sqm'].to_f
    @factor = options['@factor'].to_f
    @total_cost = @cost_per_sqm * @ink_per_sqm
  end


  after_create :set_material_cost, :set_material_charge


  A4_FACTOR = 0.0626514876
  A3_FACTOR = 0.124548139
  A2_FACTOR = 0.249096276
  A1_FACTOR = 0.499702226
  B0_FACTOR = 1.41585523
  B1_FACTOR = 0.706656651
  B2_FACTOR = 0.353328326
  B3_FACTOR = 0.176664163
  B4_FACTOR = 0.0878836952

  private



  def set_material_cost
    @material_cost = self.create_material_cost(
    cost_a4: @total_cost * A4_FACTOR,
    cost_a3: @total_cost * A3_FACTOR,
    cost_a2: @total_cost * A2_FACTOR,
    cost_a1: @total_cost * A1_FACTOR,
    cost_b0: @total_cost * B0_FACTOR,
    cost_b1: @total_cost * B1_FACTOR,
    cost_b2: @total_cost * B2_FACTOR,
    cost_b3: @total_cost * B3_FACTOR,
    cost_b4: @total_cost * B4_FACTOR
    )
  end



def set_material_charge
    @material_charge = self.create_material_charge(
    sell_a4: @total_cost * A4_FACTOR * @factor,
    sell_a3: @total_cost * A3_FACTOR * @factor,
    sell_a2: @total_cost * A2_FACTOR * @factor,
    sell_a1: @total_cost * A1_FACTOR * @factor,
    sell_b0: @total_cost * B0_FACTOR * @factor,
    sell_b1: @total_cost * B1_FACTOR * @factor,
    sell_b2: @total_cost * B2_FACTOR * @factor,
    sell_b3: @total_cost * B3_FACTOR * @factor,
    sell_b4: @total_cost * B4_FACTOR * @factor
    )

  end


    end

    class MaterialCost < ApplicationRecord
      belongs_to :material
    end

    class MaterialCharge < ApplicationRecord
      belongs_to :material
    end

代码应该是这样的吗？

Answer 1

正如 Tsao 所说，不要覆盖 initialize，但如果有，则必须调用 super。

# use '*args' so super can use any arguments to 'new'
def initialize(*args)
  # as first line so Rails will do it's "magic" before yours
  super

  # these have got values by Rails (in super) IF you have them
  # in the call to 'new'
  @cost_per_sqm = @cost_per_sqm.to_f
  @ink_per_sqm  = @ink_per_sqm.to_f
  # (you have forgot this as attr_accessor?)
  @factor       = @factor.to_f
  @total_cost   = @cost_per_sqm * @ink_per_sqm
end

但我宁愿使用另一种方法，而不是与initialize混淆

# instead of overriding 'initialize'
def init_after_create
  return if @total_cost
  # these have got values by Rails (in new) IF you have them
  # in the call to 'new'
  @cost_per_sqm = @cost_per_sqm.to_f
  @ink_per_sqm  = @ink_per_sqm.to_f
  # (you have forgot this as attr_accessor?)
  @factor       = @factor.to_f
  @total_cost   = @cost_per_sqm * @ink_per_sqm
end

def set_material_cost
  init_after_create
  @material_cost = self.create_material_cost(
  cost_a4: @total_cost * A4_FACTOR,
  cost_a3: @total_cost * A3_FACTOR,
  ....
end

def set_material_charge
  init_after_create
  @material_charge = self.create_material_charge(
  sell_a4: @total_cost * A4_FACTOR * @factor,
  sell_a3: @total_cost * A3_FACTOR * @factor,
  ...
end

提示，如果您在方法调用或Array 中将Hash 作为最后一个参数，则不必使用{ ... }

# example method
def some_method(options)
  ...
end
some_method(xxx: 1, yyy: 2)

# example array
arr = [ 1, 2, xxx: 1, yyy: 2 ]
#=> [1, 2, {:xxx=>1, :yyy=>2}]