不可能的Rails语法：命令has_many具有多态关联

Question

Statically-typed, compile-time-checked programmer brain, here, struggling with a rails function call.

In a model when we specify has_many , we can specify the sort order like this has_many :requirements, -> { order(created_at: :asc) }, :dependent => :destroy .

But when we have a polymorphic association such as this has_many :text_fields, as: :describable, :dependent => :destroy how can we add the sorting lambda?

I have tried every possible permutation of syntax except, apparently, the correct one.

Answer 1

You have clarified that it is the child records (text_fields) that you want ordered. You could use a default_scope , like so:

class ParentModel < ApplicationRecord
  has_many :text_fields, as: :describable, :dependent => :destroy
end

class TextField < ApplicationRecord
  default_scope { order(created_at: :asc) }
end

But think hard before doing so because default_scope is evil . Among other things, you can't override an order that is defined in a default_scope. I am not familiar with requirements , but you may not be able to override the order defined within requirements either.

I think you are much better served creating a scope like so:

class ParentModel < ApplicationRecord
  has_many :text_fields, as: :describable, :dependent => :destroy
end

class TextField < ApplicationRecord
  scope :default_order, -> { order(created_at: :asc) }
end

Then call it explicitly when you want your records ordered that way:

TextField.all.default_order

or

parent_record.text_fields.default_order