Rails“ has_many”關聯：“ collection =”不能按預期工作

Question

發票有許多發票分錄：

class Invoice < ActiveRecord::Base
  has_many :invoice_entries, :autosave => true, :dependent => :destroy
  validates_presence_of :date
end

class InvoiceEntry < ActiveRecord::Base
  belongs_to :invoice
  validates_presence_of :description
end

假設我們在數據庫中有一張發票：

id: 1
date: '2013-06-16'

它有兩個發票條目：

id: 10                           id: 11
invoice_id: 1                    invoice_id: 1
description: 'do A'              description: 'do C'

現在，我有了新的發票條目：

id: 10                               
description: 'do B'              description: 'do D'

(Existing invoice entry          (New invoice entry
 with updated description)        without id)

我希望發票僅具有這些新發票條目（這意味着應刪除id=11發票條目）。

invoice.invoice_entries = new_invoice_entries似乎完成了一半的工作。 它刪除id=11的發票條目，創建描述為'Do D'的新發票條目， 但不會將id=10的發票條目的描述從'Do A'為'Do B' 。 我猜想當Rails在new_invoice_entries看到一個現有的id時，它將完全忽略它。 真的嗎？ 如果是，這背后的理由是什么？

我的完整代碼如下。 您將如何解決此問題？ （我使用Rails 4，以防它簡化了代碼。）

---

# PATCH/PUT /api/invoices/5
def update
  @invoice = Invoice.find(params[:id])
  errors = []

  # Invoice entries
  invoice_entries_params = params[:invoice_entries] || []
  invoice_entries = []

  for invoice_entry_params in invoice_entries_params
    if invoice_entry_params[:id].nil?
      invoice_entry = InvoiceEntry.new(invoice_entry_params)
      errors << invoice_entry.errors.messages.values if not invoice_entry.valid?
    else
      invoice_entry = InvoiceEntry.find_by_id(invoice_entry_params[:id])

      if invoice_entry.nil?
        errors << "Couldn't find invoice entry with id = #{invoice_entry_params[:id]}"
      else
        invoice_entry.assign_attributes(invoice_entry_params)
        errors << invoice_entry.errors.messages.values if not invoice_entry.valid?
      end
    end

    invoice_entries << invoice_entry
  end

  # Invoice
  @invoice.assign_attributes(date: params[:date])

  errors << @invoice.errors.messages.values if not @invoice.valid?

  if errors.empty?
    # Save everything
    @invoice.invoice_entries = invoice_entries
    @invoice.save

    head :no_content
  else
    render json: errors.flatten, status: :unprocessable_entity
  end
end

Answer 1

要不僅更改關聯，還更改關聯對象的屬性，必須使用accepts_nested_attributes_for ：

class Invoice < ActiveRecord::Base
  has_many :invoice_entries, :autosave => true, :dependent => :destroy
  validates_presence_of :date
  accepts_nested_attributes_for :invoice_entries, allow_destroy: true
end

關於如何使用nested_attributes構建動態嵌套表單的信息，請參見第196集 。

附錄：

accepts_nested_attributes_for在嵌套哈希中期望嵌套模型的屬性，即：

invoice_params={"date" => '2013-06-16', 
  "invoice_entries_attributes" => [
    {"description" => "do A"},
    {"description" => "do B"}]
}

invoice= Invoice.new(invoice_params)
invoice.save

save將保存invoice和兩個invoice_items 。

現在

invoice=Invoice.find(1)
invoice_params={
  "invoice_entries_attributes" => [
    {"description" => "do A"},
    {"description" => "do C"}]
}
invoice.update_attributes(invoice_params)

刪除項目do B並添加項目do C

form_fields可用於創建形式，從而使這種嵌套的哈希值form_fields 。
有關詳細信息，請參見railscast。

Answer 2

嘗試使用accepts_nested_attributes_for 。 這將清理大量代碼！ 這是一個例子：

class Invoice < ActiveRecord::Base
  has_many :invoice_entries, :dependent => :destroy
  validates_presence_of :date
  attr_accessible :invoice_entries_attributes

  accepts_nested_attributes_for :invoice_entries, :allow_destroy => true
end

然后可以在視圖中使用fields_for （如果使用這些gem之一，則使用simple形式的simple_fields_for和使用fields_for semantic_fields_for ）。

<%= form_for @invoice do |invoice_form| %>
  <%= invoice_form.fields_for :invoice_entries do |invoice_entry_form| %>
    <%= invoice_entry_form.text_field :description %>
    <%= invoice_entry_form.check_box :_destroy %>
  <% end %>
<% end %>

您現在可以在控制器中重構為基礎知識：

# PATCH/PUT /api/invoices/5
def update
  @invoice = Invoice.find(params[:id])
  if @invoice.update_attributes(params[:invoice]) # This also saves all associated invoice entries, and destroy all that is marked for destruction.
    head :no_content
  else
    render json: @invoice.errors.flatten, status: :unprocessable_entity
  end
end

您可以在此處閱讀有關accepts_nested_attributes_for更多信息： http : //api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html

或者，您可以觀看有關嵌套模型的以下欄目： http ://railscasts.com/episodes/196-nested-model-form-revised