我有带有 Cancan 1.6.9 的 Rails 3 应用程序进行授权。我想将能力类转换为 JSON。这是我的能力类。
# encoding: utf-8
module Ability
def self.for(guest)
guest ||= User.new # guest user (not logged in)
if guest.admin?
AdminAbility.new(guest)
elsif guest.assurer?
AssurerAbility.new(guest)
end
end
##
# Assurer
class AssurerAbility
include CanCan::Ability
def initialize(user)
cannot :manage, User
can :read, ExchangeRate
end
end
##
# Admin
class AdminAbility
include CanCan::Ability
def initialize(user)
can :manage, User
can :manage, ExchangeRate
end
end
end
当我运行 Ability.for(User.last).to_json
时出现以下错误:
ActiveSupport::JSON::Encoding::CircularReferenceError: object references itself
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:75:in `check_for_circular_references'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:46:in `encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `block in encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `each'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `map'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:48:in `block in encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:77:in `check_for_circular_references'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:46:in `encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `block in encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `each'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `map'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:48:in `block in encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:77:in `check_for_circular_references'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:46:in `encode'
... 19 levels...
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:46:in `encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `block in encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `each'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `map'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:246:in `encode_json'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:48:in `block in encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:77:in `check_for_circular_references'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:46:in `encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/json/encoding.rb:31:in `encode'
from /home/user/.rvm/gems/ruby-1.9.3-p392@rails-3.2.13/gems/activesupport-3.2.13/lib/active_support/core_ext/object/to_json.rb:16:in `to_json'
enter code here
当我运行 Ability.for(User.last).as_json
时,我得到了结果。但它不是有效的 JSON 结果。
{"rules"=>[#<CanCan::Rule:0xaf5e81c @match_all=false, @base_behavior=false, @actions=[:manage], @subjects=[User(id: integer, password_digest: string, created_at: datetime, updated_at: datetime, uic: string, role: string, name: string, register_no: string)], @conditions={}, @block=nil>, #<CanCan::Rule:0xaf5e72c @match_all=false, @base_behavior=true, @actions=[:read], @subjects=[ExchangeRate(id: integer, data: float, date: date, created_at: datetime, updated_at: datetime)], @conditions={}, @block=nil>]}
有什么想法吗?
最佳答案
TL;DR: 在您的模型中实现 self.as_json
方法并明确指定要转换为 JSON 的字段。在此之后,您将能够运行 Ability.for(User.last).to_json
而不会出错。
完整解释:让我们看看从source看到的Ability
的结构:
Ability
实例有一个名为@rules
的字段。- 每个规则都有一个名为
@subject
的字段,它是一个扁平化的 ActiveRecord 类(User
、ExchangeRate
等)。是的,类,不是类实例。 @subject
被转换为 JSON 并出现CircularReferenceError
。为什么?
问题是,将 User
或 ExchangeRate
类转换为 JSON 不是一个好主意,因为它们的结构可能非常复杂。例如,如果您尝试运行 User.as_json
,结果可能类似于 this .可能User
的一个字段引用回User
并且您得到CircularReferenceError
。为避免这种情况,请指定哪些字段应包含在 User
的 JSON 表示中(同样适用于 ExchangeRate
):
class User < ActiveRecord::Base
#...
def self.as_json(options = {})
{ "class" => "User" }
end
end
关于ruby-on-rails - Cancan:json的能力类,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15629181/