ruby - Datamapper 的钩子(Hook)不起作用

Question

无法理解为什么 Hook 不起作用。我有以下模型:

class DirItem
  include DataMapper::Resource

  # property <name>, <type>
  property :id, Serial
  property :dir_cat_id, Integer, :required => true
  property :title, String, :required => true
  property :price, Integer, :default => 0

  belongs_to :dir_cat
  has n, :dir_photos
  has n, :dir_field_values

  before :destroy do
    logger.debug "==============DESTROYING ITEM ##{id}, TITLE
#{title}"
    dir_field_values.destroy
    dir_photos.destroy
  end
end

当我从我的应用程序或 irb 调用 destroy 方法时，它返回 false。 errors 哈希为空，日志消息不打印且记录不删除。

Answer 1

这个钩子(Hook)对我有用(ruby 1.9.2/DM 1.0.2):

require 'rubygems'
require 'dm-core'
require 'dm-migrations'


# setup the logger
DataMapper::Logger.new($stdout, :debug)

# connect to the DB
DataMapper.setup(:default, 'sqlite3::memory:')

class DirItem
  include DataMapper::Resource

  # property <name>, <type>
  property :id, Serial
  property :dir_cat_id, Integer, :required => true
  property :title, String, :required => true
  property :price, Integer, :default => 0

  has n, :dir_photos

  before :destroy do
    dir_photos.destroy
  end
end

class DirPhoto
  include DataMapper::Resource
  property :id, Serial
  belongs_to :dir_item
end

DataMapper.finalize.auto_migrate!

@i = DirItem.create(:title => 'Title', :dir_cat_id => 1)
@i.dir_photos.create
@i.dir_photos.create
@i.dir_photos.create
@i.destroy

DM 记录器显示每个 dir_photos 在 dir_item 之前被销毁。不过，您可能不希望使用钩子(Hook)，而是考虑使用 dm-constraints。像这样:

has n, :dir_photos, :constraint => :destroy

可以肯定的是，当 dir_item 被销毁时，所有的 dir_photos 都将被销毁，这也将由数据库级外键约束强制执行。