Question

我有以下脚本向我证明has_many roles=属性始终以持久的方式工作。

我的问题是：

1）这种行为背后的原因是什么：为什么has_many属性在它们被设置的那一刻就被保留了？为什么这与常规属性行为的区别（以下脚本中的name）？

2）我可以编写我的自定义roles= setter，这样我就可以使用fx assign_attributes来保存一组模型属性（包括roles =）而不保留角色关联吗？如果有可能在Rails＆gt;中我会很感激。 3.2？

这是脚本：

gem 'rails', '>=3.2.0' # change as required
gem 'sqlite3'

require 'active_record'
require 'logger'

puts "Active Record #{ActiveRecord::VERSION::STRING}"
ActiveRecord::Base.logger = Logger.new(STDERR)

ActiveRecord::Base.establish_connection(
  :adapter  => 'sqlite3',
  :database => ':memory:'
)

ActiveRecord::Schema.define do
  create_table :users, :force => true do |t|
    t.string :name
  end

  create_table :user_roles, :force => true do |t|
    t.integer :user_id
    t.integer :role_id
  end

  create_table :roles, :force => true do |t|
    t.string :name
  end
end

# Create the minimal set of models to reproduce the bug
class User < ActiveRecord::Base
  has_many :user_roles
  has_many :roles, :through => :user_roles
end

class UserRole < ActiveRecord::Base
  belongs_to :user
  belongs_to :role
end

class Role < ActiveRecord::Base
end

r = Role.create(:name => 'admin')
u = User.create

# roles= persists its value, name= does not
u.assign_attributes({ :roles => [r], :name => 'Stanislaw' })

# The same behavior is produced by:
# u.attributes=
# u.roles=

puts "name attribute: #{u.name}"
puts "many roles #{u.roles}"

u.reload

puts "name attribute: #{u.name}"
puts "many roles #{u.roles}" # I see admin role and I want to achieve behavior that I would not see it

Answer 1

关联与属性不同。例如，当你分配的是在belongs_to端设置外键时，你所做的就是has_many关联。

class User < ActiveRecord::Base
  has_many :posts
end

class Post < ActiveRecord::Base
  belongs_to :user
end

p = Post.create
u = User.create
u.posts << p # this line will simply update p.user_id with u.id

在使用连接表的示例中，为用户分配角色将创建UserRole记录并设置user_id / role_id记录。发生这种情况是因为您声明了has_many :through

至于防止此行为，您可以使用存储未使用角色的虚拟属性，直到保存记录，然后创建关联。

class User < ActiveRecord::Base
  attr_accessor :unpersisted_roles
  attr_accessible :unpersisted_roles

  after_save :assign_roles

  def assign_roles
    self.roles << @unpersisted_roles if defined(@unpersisted_roles)
  end
end

r = Role.create
u = User.create
u.attributes = {:unpersisted_roles => [r]}
u.save # roles get persisted here

这只是一个简单的例子，实际代码可能需要更复杂，或者需要深入了解AR的界面以使其工作而不会产生太多副作用。

如果你能够提供一些见解，告诉你为什么不想坚持这种关联，我可能会提出一个更具体的行动方案。

的更新

参考Issue #3并提供一些评论，其中包含更改。

module SimpleRoles module Many module Persistence class << self def included base base.class_eval %{ has_many :user_roles has_many :roles, :through => :user_roles # Add a callback to persist the roles after_create :persist_roles } end end def roles # Apply unpersisted roles in case we want to access them before saving super.map(&:name).map(&:to_sym) + (@unpersisted_roles || []) end def roles= *rolez rolez.to_symbols!.flatten! # if we're already persisted then go ahead and save # otherwise stash them in an ivar array if persisted? super retrieve_roles(rolez) else @unpersisted_roles = rolez end end private # Our callback method that sets the roles, this will # work since persisted? is true when this runs. def persist_roles self.roles = @unpersisted_roles end def retrieve_roles rolez raise "Not a valid role!" if (rolez - config.valid_roles).size > 0 rolez.map do |rolle| begin Role.find_by_name! rolle.to_s rescue raise "Couldn't find Role for #{rolle}. Maybe you need to re-run migrations?" end end end def config SimpleRoles::Configuration end end end end

has_many关联属性setter是否始终将其值保存到数据库中，是否可以使其不可用？

1 个答案: