Question

I have a method that will provide an array of model object. Some of those model’s attributes are easy to sort by using some help from SQL. I mean, using .find(:condition => {})

The problem is some of the other attributes isn’t. It has to be calculated, modified, or did something else before showing. Then, I found the way to sort it using collection sorting. Which is, collection.sort{|a,b| a.something_to_sort <=> b.something_to_sort}

OK! That’s works. But the problem is, is it possible to make that something_to_sort part to become a dynamic variable? For example, I want to take a parameter from the UI and assign it to that something_to_sort like following,

HTML

<select name="sort">
    <option value="name">Name</option>
    <option value="age">Age</option>
    <option value="activity.category">Activity</option>
    <option value="tax.calculate_personal_income_tax">Income Tax</option>
    <option value="tax.calculate_withholding_tax">Withholding Tax</option>
    <option value="doctor.name">Doctor's Name</option>
</select>

Rails

params[:sort] ||= "Age"
@people = Person.find(:all)
@people.sort{|a,b| a.params[:sort] <=> b.params[:sort]}    #Note that this is an incorrect syntax

Is there any way to do this by not having to write a sort block for each of sorting option?

Additional #1

I’ve just tried this and it was working for some sorting option

@people.sort{|a,b| a.send(params[:sort]) <=> b.send(params[:sort])}

This works for name and age as they are people’s attribute (and it works for peopls’s method too). But for the association’s such as tax.calculate_personal_income_tax, it’s not.

So, my colleague told me to create new people’s method, calculate_personal_income_tax and then change the option value from tax.calculate_personal_income_tax to calculate_personal_income_tax so that the send method will be able to find this method …

def calculate_personal_income_tax
    tax.calculate_personal_income_tax
end

But, this is not really what I want. Because I believe that there must be a way to access this association method without having to define a new model method. If I choose to do this and one day people model become larger, more attribute, more information to sort and display. Then, there will be a lot of method like this.

The other reason is, if I have to define a new method, that method should have to do some logic, calculation or else, not just retrieve a data from other model.

Additional #2

Finally, I’ve just found the way to access other model attribute by adding args to the find method, :join and :select.

@people = Person.find(:all, :select => "persons.*, tax.tax_rate AS tax_rate", :joins => :tax, :condition => {some conditions})

The result of that will be a table of person joining with tax. Then, I use the send(params[:sort]) thing to help me sorting the attribute that I want.

Answer 1

@people.sort {|a, b| a.send(params[:sort]) <=> b.send(params[:sort])}