Question

我的架构看起来像这样：

create_table "customers" do |t|
  t.integer "customer_number"
end

create_table "past_payments" do |t|
  t.integer  "customer_number"

  t.datetime "transaction_date"
  t.integer  "arbitrary_sequence_number"
end

create_table "payment_details" do |t|
  t.datetime "transaction_date"
  t.integer  "arbitrary_sequence_number"
end

TL;来自架构的DR - 客户通过主/外键与past_payment相关联。并且，当其transaction_date AND arbitrary_sequence_number相等时，PastPayment与单个PaymentDetail相关联。付款和明细没有正式的主要/外键关系。

这给了我以下的ActiveRecord模型：

class Customer < ActiveRecord::Base
  has_many :past_payments, foreign_key: :customer_number, primary_key: :customer_number

  has_many :payment_details, through: :past_payments # unfortunately, broken 
end

class PastPayment < ActiveRecord::Base
  has_one :payment_detail, ->(past_payment) {
    where(arbitrary_sequence_number: past_payment.arbitrary_sequence_number)
  }, foreign_key: :transaction_date, primary_key: :transaction_date
end

由于Customer has_many :past_payments和PastPayment has_one :payment_detail，我认为有一个关联可以定义为Customer has_many :payment_details, through: :past_payments，但由于范围我无法使其工作在has_one :payment_detail协会上定义。

具体来说，调用Customer.payment_details会提升NoMethodError: undefined method 'arbitrary_sequence_number' for #<Customer:0x2i8asdf3>。因此，与PastPayment相反，客户似乎会被传递到我的范围。

是否可以在客户上定义has_many :payment_details关联？我做错了吗？

要明确的是，我希望能够说出Customer.where(some_conditions).includes(:payment_details)并执行两个查询，所以如果有办法在没有关联的情况下实现这一点，我就会接受它。

注意：我无法更改此数据库。它是一些其他应用程序写入的数据库，我需要从中读取它。

与我的问题无关，这是我目前正在使用的解决方法。如果没有办法正确使用关联，我很乐意批评这个解决方案：

class Customer < ActiveRecord::Base
  attr_writer :payment_details

  def payment_details
    @payment_details ||= Array(self).with_payment_details.payment_details
  end

  module InjectingPaymentData
    def with_payment_details
      results = self.to_a
      return self unless results.first.is_a?(Customer)

      user_ids = results.collect(&:id)

      # i've omitted the details of the query, but the idea is at the end of it
      # we have a hash with the customer_number as a key pointing to an array
      # of PaymentDetail objects
      payment_details = PaymentDetails.joins().where().group_by(&:customer_number)

      results.each do |customer|
        customer.payment_details = Array(payment_details[customer.customer_number])
      end
    end
  end
end

ActiveRecord::Relation.send(:include, Customer::InjectingPaymentData)
Array.send(:include, Customer::InjectingPaymentData)

然后我可以通过最少的查询来执行以下操作：

@customers = Customer.where(id: 0..1000).with_payment_details
@customers.each { |c| do_something_with_those_payment_details }

该方法存在问题？

Answer 1

您可以利用此gem更好地处理＆＃34;复合主键＆＃34;在ActiveRecord中：https://github.com/composite-primary-keys/composite_primary_keys

class Customer < ActiveRecord::Base
  has_many :past_payments, foreign_key: :customer_number, primary_key: :customer_number

  has_many :payment_details, through: :past_payments # this works now
end

class PastPayment < ActiveRecord::Base
  has_one :payment_detail, foreign_key: [:transaction_date, :arbitrary_sequence_number],
                           primary_key: [:transaction_date, :arbitrary_sequence_number]
end

在直通模型

1 个答案: