Question

I have some STI structure like following:

class Assignment < ActiveRecord::Base 
  has_many :criteria, :class_name => "Criterion", :order => :position
end

class Criterion < ActiveRecord::Base
  # Represents a criterion used to mark an assignment that
  # being the super class for all different criterias
  set_table_name "criteria" # set table name correctly
  belongs_to  :assignment
  validates_associated :assignment, :message => 'association is not strong with an assignment'
  validates_presence_of :assignment_id
  validates_numericality_of :assignment_id, :only_integer => true, :greater_than => 0, :message => "can only be whole number greater than 0"
  validates_uniqueness_of :criterion_name, :scope => :assignment_id, :message => 'is already taken'
  validates_presence_of :criterion_name,:assignment_id
end

class FlexibleCriterion < Criterion
  has_one :flexible_criterion_attribute, :class_name => "FlexibleCriterionAttribute"
  accepts_nested_attributes_for :flexible_criterion_attribute
  default_scope :include => :flexible_criterion_attribute
end

class FlexibleCriterionAttribute < ActiveRecord::Base
  belongs_to  :criterion, :class_name => "FlexibleCriterion"
  validates_presence_of :max
  validates_numericality_of :max, :message => "must be a number greater than 0.0", :greater_than => 0.0

  DEFAULT_MAX = 1

end

好的，我上传了我当前的工作代码。基本上问题是：当我使用像criterion = assignment.criteria.find_or_create_by_criterion_name（“AAA”）这样的方法时，我将得到一个标准对象。但是我希望将此对象转换为flexiblecriterion，以便我可以赋值standard.flexible_criterion_attribute

Thx in advance!

Answer 1

如果assignment.criteria.find_or_create_by_criterion_name("AAA")返回type列的值为FlexibleCriterion的记录，则会自动将对象转换为FlexibleCriterion。
如果您想确保只返回FlexibleCriterion，请修改您的查找器，如下所示：assignment.criteria.find_or_create_by_criterion_name_and_type("AAA", 'FlexibleCriterion')

在Rails中调用child的方法或将父级转换为子级

1 个答案: