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I have an ActiveRecord query user.loans, and am using user.loans.map(&:dup) to duplicate the result. This is so that I can loop through each Loan (100+ times) and run several calculations.

These calculations take several seconds longer compared to when I run them directly on user.loans or user.loans.dup. If I do this however, all queries user.loans are affected, even when querying with different methods.

Is there an alternative to .map(&:dup) that can achieve the same result with faster calculations? I'd like to preserve the relations so that I can retrieve associated records to each Loan.

Luke Keller
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    Perhaps you should be doing your calculations in SQL? Can you give an example of the calculations you're doing? – Chris Heald Sep 15 '15 at 01:31

2 Answers2

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The fastest way you can achieve what you want is making calculations directly on ActiveRecord, this way you would not have to loop through resulting Array.

If you still want to loop through Array elements, maybe you should not use map to duplicate each Array element. You could use each instead, which does not affect original Array element. Here is what I think you should do: 

def calculate_loans
  calculated_loans = Array.new    
  user.loans.each do |loan|
    # Here you make your calculations. For example:
    calculated_loans.push(loan.value += 10)
  end
  calculated_loans
end

This way, you will have original user.loans elements, and a duplicated Array with calculated_loans.

Please, let me know if this improve your performance :)

Community
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Daniel Batalla
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  • Hey Daniel, ActiveRecord is definitely the way to go, but it doesn't resolve the issue mentioned in the second paragraph of my question. To use ActiveRecord and manipulate the loan objects without affecting other loan data, I wound up using `.reload` on calls to loans outside of the calculations. – Luke Keller Sep 17 '15 at 12:54
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To resolve conflicts with other calls to user.loans, I wound up using user.loans.reload in the Presenter I have for this particular view. This way I was able to continue making calculations directly on Active Record elsewhere(per Daniel Batalla's suggestion), but without the conflicts I mentioned in my original question.

Luke Keller
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