refactoring ruby: want to pass attribute name into a method

Question

I have a DataPoint model where I have three methods that do the same thing, just on different fields in the data_points database.

def self.currently_employed(data_points)
    data_points.where(currently_employed: true).count / data_points.count.to_f * 100
end

def self.undergrad_degree(data_points)
    data_points.where(undergrad_degree: true).count / data_points.count.to_f * 100
end

def self.grad_degree(data_points)
    data_points.where(grad_degree: true).count / data_points.count.to_f * 100
end

I think I should be able to refactor this to accept which column to perform the calculation on as a parameter, but much time on the internet / trying stuff out hasn't yielded results.

Could someone please advise me on whether / how I could refactor this to a single method?

In case it affects the answer: the data_points argument is a subset of DataPoint.all specified by the User - i.e. User types in what age, years work experience, etc. they want to see results for (age & years_work_experience are DataPoint attributes), and then I want to show summary stats for that subset.

Thanks!

Ajedi32 · Accepted Answer · 2015-06-05 20:27:36Z

1

The name of the attribute is really just a key in a hash.

data_points.where(currently_employed: true)

Is equivalent to

data_points.where({:currently_employed => true})

With this in mind, it's easy to refactor these methods into one:

def self.percent_with_attribute(data_points, attribute)
    data_points.where(attribute => true).count / data_points.count.to_f * 100
end

answered Jun 5, 2015 at 20:27

Ajedi32

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Comments

Achrome · Accepted Answer · 2015-06-05 20:31:38Z

0

You can use string interpolation here.

def self.status(data_points, key)
  data_points.where("#{key}": true).count / data_points.count.to_f * 100
end

How it differs from @Ajedi32's answer is only in that the key here will be converted to a Symbol, instead of a plain String.

answered Jun 5, 2015 at 20:31

Achrome

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3 Comments

Ajedi32 Over a year ago

To clarify, my answer only passes the attribute as a string if the attribute argument given to percent_with_attribute was already a string. If the attribute argument was a symbol, it will be passed as a symbol. This answer converts the argument to a symbol regardless of whether it was passed as a string, symbol, or any other object that responds to to_s. In practice, there's probably not any real significant difference between these two approaches, since AFAIK Rails treats string and symbol keys identically.

Achrome Over a year ago

That's correct, but I thought I would provide the alternative solution as well.

Achrome Over a year ago

No. There isn't. Except the syntax for the hash will change to key.to_sym => true.

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