ruby-on-rails – 访问Rails中未保存的父级和子级的祖父母

class Grandparent < ApplicationRecord
  # before_add and after_add are two callbacks specific to associations
  # See: http://guides.rubyonrails.org/association_basics.html#association-callbacks
  has_many :parents,inverse_of: :grandparent,before_add: :run_before_add,after_add: :run_after_add

  # We will use this to test in what sequence callbacks/initializers are fired
  def self.test
    @grandparent = Grandparent.first

    # Excuse the poor test parameters -- I set up a bare Rails project and
    # did not define any columns,so created_at and updated_at was all I
    # had to work with
    parent_params =
      {
        created_at: 'now',children_attributes: [{created_at: 'test'}]
      }

    # Let's trigger the chain of initializations/callbacks
    puts 'Running initialization callback test:'
    @grandparent.parents.build(parent_params)
  end

  # Runs before parent object is added to this instance's #parents
  def run_before_add(parent)
    puts "before adding parent to grandparent"
  end

  # Runs after parent object is added to this instance's #parents
  def run_after_add(parent)
    puts 'after adding parent to grandparent'
  end
end

class Parent < ApplicationRecord
  belongs_to :grandparent,inverse_of: :parent,after_add: :run_after_add
  accepts_nested_attributes_for :children

  def initialize(attributes)
    puts 'parent initializing'
    super(attributes)
  end

  after_initialize do
    puts 'after parent initialization'
  end

  # Runs before child object is added to this instance's #children    
  def run_before_add(child)
    puts 'before adding child'
  end

  # Runs after child object is added to this instance's #children
  def run_after_add(child)
    puts 'after adding child'
  end
end

class Child < ApplicationRecord
  # whether it's the line below or
  # belongs_to :parent,inverse_of: :children
  # makes no difference in this case -- I tested :)
  belongs_to :parent
  delegate :grandparent,to: :parent

  def initialize(attributes)
    puts 'child initializing'
    super(attributes)
  end

  after_initialize do
    puts 'after child initialization'
  end
end

从Rails控制台运行方法Grandparent.test输出：

Running initialization callback test:
parent initializing
child initializing
after child initialization
before adding child
after adding child
after parent initialization
before adding parent to grandparent
after adding parent to grandparent

你可以从中看到的是,直到最后,父母实际上并没有被添加到祖父母.换句话说,在子初始化和自己的初始化结束之前,父母不知道祖父母.

如果我们修改每个puts语句以包含grandparent.present ?,我们得到以下输出：

Running initialization callback test:
parent initializing: n/a
child initializing: n/a
after child initialization: false
before adding child: false
after adding child: false
after parent initialization: true
before adding parent to grandparent: true
after adding parent to grandparent: true

因此,您可以先执行以下操作,首先初始化父项,然后初始化子项(ren)：

class Parent < ApplicationRecord
  # ...
  def initialize(attributes)
    # Initialize parent but don't initialize children just yet
    super attributes.except(:children_attributes)

    # Parent initialized. At this point grandparent is accessible!
    # puts grandparent.present? # true!

    # Now initialize children. MUST use self
    self.children_attributes = attributes[:children_attributes]
  end
  # ...
end

以下是运行Grandparent.test时输出的内容：

Running initialization callback test:
before parent initializing: n/a
after parent initialization: true
child initializing: n/a
after child initialization: true
before adding child: true
after adding child: true
before adding parent to grandparent: true
after adding parent to grandparent: true

如您所见,父级初始化现在在调用子初始化之前运行并完成.

但明确地将祖父母：@grandparent传递给params哈希可能是最简单的解决方案.

当您在传递给@ grandparent.parents.build的params哈希中明确指定祖父项：@grandparent时,祖父表从一开始就被初始化.可能是因为#initialize方法运行后会立即处理所有属性.这是看起来像：

Running initialization callback test:
parent initializing: n/a
child initializing: n/a
after child initialization: true
before adding child: true
after adding child: true
after parent initialization: true
before adding parent to grandparent: true
after adding parent to grandparent: true

您甚至可以直接在控制器方法#parent_params中调用merge(grandparent：@grandparent),如下所示：

def parent_params
    params.require(:parent).permit(
      :parent_attribute,children_attributes: [
        :some_attribute,:_destroy
      ]
    ).merge(grandparent: @grandparent)
end

PS：为过长的答案道歉.