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。一次致电Invoice#save!，一切都被保存。

> 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，当我尝试更新已存在的Invoice项时，会在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

如何在调用Invoice#save!时告诉ActiveRecord删除旧项目？或者这是ActiveRecord中的错误吗？

编辑：我的问题 - 澄清

我不希望在分配项目（DELETE）时运行i.items = ...个查询，但保存包含项目的发票时invoice.save!）。它应标记旧项目以进行删除，并将新项目标记为插入，然后在invoice.save!上执行查询。这可能与ActiveRecord有关吗？

编辑2：进一步澄清

由于有些人不能正确回答问题，因此需要进一步澄清。我必须承认，这非常复杂。所以这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

此不会发生。我希望它发生。这完全是虚构的。将其与上面的列表进行比较，看看差异。

# (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

实际上是什么

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

Answer 1

它会删除旧项目，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，它会起作用。

Answer 2

由于您希望在作业中添加动作，我相信这应该有效：

  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选项配置关联，并使用mark_for_destruction在save上指定要销毁的每个物品。

考虑第二次修改，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

保存模型时删除关联的记录