Intro

Recently, I was tasked with creating a calculation to run an Oban job using ash_oban. I needed to determine whether a specific record met the criteria using this calculation. Here's what I did to achieve that.

calculations do
    calculate :should_this_record_run_oban_job?, :boolean do
       calculation expr(
         # this is where the problem I need to solve.
         true
       )
    end
end

Problem 1: How can I build the criteria that I need?

calculations do
    calculate :should_this_record_run_oban_job?, :boolean do
       calculation expr(
         # this is where the problem I need to solve.
         true
       )
    end
end

When performing calculations, you can use fragments or directly access the attributes needed to create specific conditions. Initially, I did something like this.

calculations do
    calculate :should_this_record_run_oban_job?, :boolean do
       calculation expr(
         inserted_at <= ago(24, :hour) and name == "freddy" and 
         age >= 18
       )
    end
end

It seems pretty straightforward right? BUT what I discovered is somehow more readable and organized.

What I discovered

What I discovered is that, you can create multiple calculations and combine them according to your needs.

calculations do
    calculate :active_last_24_hours_ago?, :boolean do
        calculation expr(inserted_at <= ago(24, :hour)
    end

    calculate :is_his_name_freddy?, :boolean do
        calculation expr(name == "freddy")
    end

    calculte :is_age_18_or_more?, :boolean do
        calculation expr(age >= 18)
    end

    calculate :should_this_record_run_oban_job?, :boolean do
       calculation expr(
         active_last_24_hours_ago? and is_his_name_freddy? and is_age_18_or_more?
       )
    end
end