Question

数据库是否只允许一行（例如，用于站点范围的设置）？

Answer 1

class Whatever < ActiveRecord::Base
  validates :there_can_only_be_one

  private

  def there_can_only_be_one
    errors.add_to_base('There can only be one') if Whatever.count > 0
  end
end

Answer 2

在Rails 4中：

class Anything < ActiveRecord::Base
  before_create :only_one_row

  private
  def only_one_row
    false if Anything.count > 0
  end
end

无声错误很糟糕，然后

class Anything < ActiveRecord::Base
  before_create :only_one_row

  private
  def only_one_row
    raise "You can create only one row of this table" if Anything.count > 0
  end
end

Answer 3

这一行中只有一列吗？如果没有，则添加具有迁移的新列可能会过度。您至少可以使此表包含“名称”和“值”列，并按名称上的唯一性进行验证。

Rails ActiveRecord数据库只有一行

3 个答案: