Rails：从出生日期起从 model 的所有实例中获取平均值

Question

Im kinda new to the dev world and have the next issue:

I need to display the average age from a group of people. Since i cannot have an "age" property in the model, i defined the age method on the class as follows:

class Persona < ApplicationRecord


require 'date'
    def age
      now = Time.now.utc.to_date
      dob = self.fecha_de_nacimiento
      now.year - dob.year - ((now.month > dob.month || (now.month == dob.month && now.day >= dob.day)) ? 0 : 1)
    end
end

This is my controller:

 def index
@personas = Persona.order(Arel.sql("cast(strftime('%m', fecha_de_nacimiento) as integer)"))

This is because I need to have the table ordered by month of birth on the index view.

Now I need to show the average age of Persona, but have tried with persona.average(age), persona.average(:age) and so on and cant seem to get it to work. Is there a way to do it with average or to make the sum of all ages and then divide it by the total number of my persona instances?

Thanks in advance to anyone who might help me.

Answer 1

Just found the way to make it work, If anyone needs it. what I did was just sum all the ages and then divide it by @personas:lenght in my view with embedded ruby like this:

<p>


El promedio de edad es:
  <%= @personas.sum(&:age) / @personas.length %>
</p>

And it worked fine just like that!

This older answer really helped. Rails 4 Sum by Model Method

Hope this helps anyone else!