Rails 中的多态性“未初始化常量”错误

Question

我想在我的项目中建立多态关联，所以我按照 Rails 指南去做，但我得到了：NameError: uninitialized constant DashboardAssignment::Assignable 错误。

型号：

仪表板分配：

class DashboardAssignment < ActiveRecord::Base
  belongs_to :dashboard
  belongs_to :assignable, polymorphic: true

  validates :dashboard, presence: true
  validates :assignable, presence: true, uniqueness: { :scope => :dashboard }
end

用户：

class User < ActiveRecord::Base
  has_many :dashboard_assignments, as: :assignable
  has_many :dashboards, through: :dashboard_assignments
end

组：

class Group < ActiveRecord::Base
  has_one :dashboard_assignment, as: :assignable
  has_many :laboratories_assignments, as: :lab_assignable
end

仪表板：

class Dashboard < ActiveRecord::Base
  has_one :building
  has_many :dashboard_assignments
  has_many :users, through: :dashboard_assignments, as: :assignable
end

在 DashboardAssignment Migration 文件中我有：

t.references :assignable, null: false, polymorphic: true, index: true

当我尝试通过 DashboardAssignment.create(assignable: u) 创建新的 DashboardAssignment 时，u = User.find(1) 它给了我错误：

NameError: uninitialized constant DashboardAssignment::Assignable
    from P:/Ruby23-x64/lib/ruby/gems/2.3.0/gems/activerecord-4.2.6/lib/active_record/inheritance.rb:158:in `compute_type' ...

我做错了吗？

我的 rails 版本是 4.2.6

Answer 1

您应该在 through 关联中使用 source 而不是 as

class Dashboard < ActiveRecord::Base
  has_one :building
  has_many :dashboard_assignments
  has_many :users, through: :dashboard_assignments, source: :assignable
end

我会提醒您，这可能会给您assignables 属于Group 类。解决此问题的最佳方法是为dashboard_assignments 添加一个条件到has_many，让您只过滤具有assignable_type = 'User' 的dashboard_assignments：

class Dashboard < ActiveRecord::Base
  has_one :building
  has_many :user_dashboard_assignments, -> { where(assignable_type: 'User') }, class_name: 'DashboardAssignment'
  has_many :users, through: :user_dashboard_assignments, source: :assignable
end