你如何在带有 PostgreSQL 的 Rails 中查询 3 个不同的模型？

Question

I need to write a query in Rails that involves 3 different models. I need to know which Subscriptions are delivereable. But delivereable is not a column in Subscription but in BasePlan.

class BasePlan
  has_many :plans
end

class Plan
  has_many :subscriptions
end

class Subscription
  belongs_to  :plan
end

I've tried joining all three models together to no success:

Subscription.joins(:plans).joins(:base_plans).where(queried_column: true)

What would be the right way to write the query?

Answer 1

Subscription needs to know about it's relationship to :base_plans for your code to work.

class Subscription
  belongs_to :plan
  has_one :base_plan, through: :plan
end

Answer 2

Using @SteveTurczyn 's answer, you could query like this: Subscription.joins(:base_plan).where(base_plans: { queried_column: true }) . You need to first define the through relationship as Steve suggests, then you can traverse the relationship to get the column you need to check on BasePlan.