保存模型时删除关联记录

Question

我正在运行 ActiveRecord 3.2.6。鉴于我有这些模型定义：

我的发票模型

class Invoice < ActiveRecord::Base
  has_many :items, :autosave => true, :dependent => :delete_all
  attr_accessible :recipient_email

  # This is just a simple wrapper with allows me to build multiple
  # items at once and to specify them as a Hash instead of Item.new.
  def items=(ary)
    super ary.map{|item| item.is_a?(Hash) ? items.build(item) : item}
  end
end

我的项目模型

class Item < ActiveRecord::Base
  belongs_to :invoice

  attr_accessible :amount, :description, :invoice_id, :value
end

我的目标是将发票项目直接保存在模型中。当新创建发票时，这没有问题。拨打Invoice#save! 即可保存所有内容。

> i = Invoice.new(:recipient_email => "foobar@example.org")
> i.items = [{amount: 10, description: "Bottles of Milk", value: 0.40},
  {amount: 1, description: "Shipping fee to Antarctica", value: 217.38}]
> i.save!
  SQL (23.5ms)  INSERT INTO "invoices" [...]
  SQL (0.3ms)  INSERT INTO "items" [...]
  SQL (0.2ms)  INSERT INTO "items" [...]
 => true 

但是，当我尝试更新 Invoice 中已经存在的项目时，它会在我保存新项目之前删除旧项目。

# Load invoice ID 1, with two items: ID 1 and ID 2.
> i = Invoice.find(1)

# It deletes the old items here
> i.items = [{amount: 10, description: "Less buggy objective relational mappers", value: 1337.00}]
  SQL (0.8ms)  DELETE FROM items WHERE id IN (1, 2)

# But it should delete the new items here, before inserting the new items,
# wrapping everything in a transaction.
> i.save!
  SQL (1.0ms)  INSERT INTO "items" [...]
   (192.6ms)  commit transaction

如何告诉 ActiveRecord 仅在调用 Invoice#save! 时删除旧项目？或者这是 ActiveRecord 中的错误？

编辑：我的问题 - 澄清

我不希望在分配项目 (i.items = ...) 时运行 DELETE 查询，但在保存包含项目的发票时 (invoice.save!)。它应该将旧项目标记为删除，将新项目标记为插入，然后在invoice.save! 上执行查询。 ActiveRecord 可以做到这一点吗？

编辑 2：进一步澄清

由于有些人没有正确回答问题，因此需要进一步澄清。我必须承认，这很复杂。所以这就是实际发生的事情和我想要发生的事情之间的区别。

我想要什么

这不会发生。我希望它发生。这完全是虚构的。将其与上面的清单进行比较，看看有什么不同。

# (1) Load invoice ID 1, with two items: ID 1 and ID 2.
> i = Invoice.find(1)

# (2) Assign new items, delete the old ones. New stuff exists in memory, not in database
> i.items = [{amount: 10, description: "Less buggy objective relational mappers", value: 1337.00}]

# (3) Save everything to database. Run queries.
> i.save!
   (0.0ms) begin transactions
  SQL (0.8ms)  DELETE FROM items WHERE id IN (1, 2)
  SQL (1.0ms)  INSERT INTO "items" [...]
   (192.6ms)  commit transaction

实际发生了什么

DELETE 查询在点 (2) 处运行。但它应该在(3) 点运行。 （与上面的清单相比）。

Answer 1

它将删除旧项目，因为您将关联配置为自动保存

has_many :items, :autosave => true, :dependent => :delete_all

删除自动保存并重试，它会工作。

Answer 2

由于您想在作业中附加操作，我相信这应该可行：

  def items=(ary)
    super(ary.map{|item| item.is_a?(Hash) ? items.build(item) : item} + self.items)
  end

Answer 3

您可以使用autosave: true 选项配置您的关联，并使用mark_for_destruction 指定您要在save 上销毁的每个项目。

考虑到您的第二次编辑，您可以执行以下操作：

# (1) Load invoice ID 1, with two items: ID 1 and ID 2.
> i = Invoice.find(1)

# (2) Mark the old items to be destroyed on save. They are still in memory and in the database for now.
> i.items.each(&:mark_for_destruction)

# (3) Assign new items. New stuff exists in memory, not in database.
> i.items.build([{amount: 10, description: "Less buggy objective relational mappers", value: 1337.00}])

# (4) Delete the items which has been mark for destruction. Save everything to database. Run queries.
> i.save!
   (0.0ms) begin transactions
  SQL (0.8ms)  DELETE FROM items WHERE id IN (1, 2)
  SQL (1.0ms)  INSERT INTO "items" [...]
   (192.6ms)  commit transaction