ActiveRecord Rails 如何在多态关联中查询关联模型

Question

I have a polymorphic association on my PartnerItem model :

class PartnersItem < ApplicationRecord
  belongs_to :item, polymorphic: true
  belongs_to :partner
end

Item can be a program or a session

Program is also linked to sessions in a has_many relationship : Program has_many Sessions

I need to find all Programs to which a partner_item is linked. That means

Any program / item associated to a specific partner

Any program linked to a session/item associated to a specific partner.

Finally the query results need to be unique, meaning a Program can't appear twice in the results

I am having a hard time figuring out how to assemble such query.

This retrieves all items for a specific partner but Im stuck on what are the next steps

  PartnerItem.where(
     partner: current_partner
   ).items

Answer 1

One way to do could be like this:

program_ids = PartnerItem.where(partner: current_partner, item_type: 'Program').pluck(:item_id)
program_ids += Session.joins(:partner_items).where(partner_items: { partner_id: partner.id }).where.not(program_id: nil).pluck(:program_id)
Program.where(id: program_ids.uniq)

This would probably return all the Program records which have a PartnerItem directly or through Session .

Answer 2

partner_items = PartnerItem.where(partner: current_partner) problem_ids = partner_items.filter { |x| x.item_type == "Program" }.map(&:item_id) session_ids = partner_items.filter { |x| x.item_type == "Session" }.map(&:item_id) Problem.joins(:sessions) .where("problems.id IN (?) OR sessions.id IN (?)", problem_ids, session_ids) .distinct

Answer 3

If I understand correctly, this is almost what you:

current_partner.partners_items

want except then you get models with a reference to the program or to the session and when the session you want the program it belongs to.

In SQL this would be:

SELECT programs.*
FROM programs
  INNER JOIN partners
    ON partners.item_type = 'Program' and partners.item_id = programs.id
WHERE partners.id = ?

UNION

SELECT programs.*
FROM programs
  INNER JOIN sessions
    ON sessions.program_id = programs.id
  INNER JOIN partners
    ON sessions.item_type = 'Session' and partners.item_id = sessions.id
WHERE partners.id = ?

Because the joins have a different structure the SQL is going to need a UNION or a subquery which is hard to express in one query using ActiveRecord.

First I would add scopes for the polymorphic types.

class PartnersItem < ApplicationRecord
  belongs_to :item, polymorphic: true
  belongs_to :partner

  scope :programs, -> { where(type: 'Program') }
  scope :sessions, -> { where(type: 'Session') }
end

Then you might query for the program ids and the session ids for the current partner and use that in the final query.

partner_program_ids = current_partner.partners_items.programs.pluck(:id)
partner_session_ids = current_partner.partners_items.sessions.pluck(:id)

Program.joins(:session)
    .where("programs.id = :partner_program_ids
           OR sessions.id = :partner_session_ids",
           partner_program_ids: partner_program_ids,
           partner_session_ids: partner_session_ids)