Ruby-on-rails – Converting an array of objects to ActiveRecord::Relation

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I have an array of objects, let's call it an Indicator. I want to run Indicator class methods (those of the def self.subjects variety, scopes, etc) on this array. The only way I know to run class methods on a group of objects is to have them be an ActiveRecord::Relation. So I end up resorting to adding a to_indicators method to Array.

def to_indicators
  # TODO: Make this less terrible.
  Indicator.where id: self.pluck(:id)
end

At times I chain quite a few of these scopes to filter down the results, within the class methods. So, even though I call a method on an ActiveRecord::Relation, I don't know how to access that object. I can only get to the contents of it through all. But all is an Array. So then I have to convert that array to a ActiveRecord::Relation. For example, this is part of one of the methods:

all.to_indicators.applicable_for_bank(id).each do |indicator|
  total += indicator.residual_risk_for(id)
  indicator_count += 1 if indicator.completed_by?(id)
end

I guess this condenses down to two questions.

  1. How can I convert an Array of objects to an ActiveRecord::Relation? Preferably without doing a where each time.
  2. When running a def self.subjects type method on an ActiveRecord::Relation, how do I access that ActiveRecord::Relation object itself?

Thanks. If I need to clarify anything, let me know.

Best Answer

You can convert an array of objects arr to an ActiveRecord::Relation like this (assuming you know which class the objects are, which you probably do)

MyModel.where(id: arr.map(&:id))

You have to use where though, it's a useful tool which you shouldn't be reluctant to use. And now you have a one-liner converting an array to a relation.

map(&:id) will turn your array of objects to an array containing only their id's. And passing an array to a where clause will generate a SQL statement with IN that looks something like:

SELECT .... WHERE `my_models`.id IN (2, 3, 4, 6, ....

Keep in mind that the ordering of the array will be lost - But since your objective is only to run a class method on the collection of these objects, I assume it won't be a problem.

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