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I have a model students. in studentsController I select a collection of students. I want to attach a flag to the first and the last record.

I'll display the list of students with a partial like this: students/_student and when a user clicks each student, they'll get a popup.

I want to use the flag to determine whether this student is the first/last so that I can add a query parameter to the url. So for instance, the url will look like this when you hover over the first student: localhost:3000/student/1?location=first

When displaying though a partial, the collection is not present in the partial, and so I cannot just do a test like this: student.first?

Any ideas? Thank you.

[EDIT]. This was originally a reply to @neils, but I figured I'd put it out there: It works however I have another issue. Because I'm using an "auto-scroll" feature, which loads in more students as the user scrolls down the page ( 3 at a time), the "first" and "last" gets added to the first and third student of each row rather than the actual first and last of the collection. The way I do the auto-scroll: I use $.getScript to request the index.js.erb file. That file renders the students/_student like so: render @students, and attach to a container div. I render the url in that template (students/_student), so the params gets rendered every first/third time.

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  • why don't you use params[:location] as you are passing it in url?? Commented Sep 4, 2012 at 18:37
  • Please add some code so that its easy to solve the problem. Commented Sep 4, 2012 at 18:43
  • @Sush I'm not sure I understand what you mean. I will use params[:location] to get it back and figure out whether it's the first or last item. My problem is attaching the location params to the url in the first place. I need to figure when to attach it, and so I need to know which item is the first and which one is the last. Commented Sep 4, 2012 at 18:57
  • @soundar I'm at the day job right now, so I can't paste in any code until later on. Is there something specific you want me to explain? Thanks for your response. Commented Sep 4, 2012 at 18:58
  • ok.Are you rendering the students like render "student", :collection => @students ? Commented Sep 4, 2012 at 19:07

3 Answers 3

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You can proceed with your render @students call if you want. Just take note that you magically have a student_counter helper available for you in your partial when you do that. Now in your partial, you can compare the student_counter with @students.size and set your link_to's :location=>'first/last' via helper or decorator.

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I will definitely try this out. Thank you!
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Assuming that you already assign some collection of students to @students (Student.all, Student.where(some_conditions), whatever...) in your controller, you could do the following:

Add attr_accessor :flag to your Student model:

class Student < ActiveRecord::Base
  attr_accessor :flag
  #... rest of your code
end

This creates an non-ActiveRecord attribute on you Student instances.

Than you could do something in the controller like: 

@students[0].flag = 'first'
@students[-1].flag = 'last'

and then use that info in your view. Not really elegant, but it should do the trick.

EDIT: Elaborated the above a bit, to make it more clear. EDIT2: Fixed mistake, attr_accessor is the right method, not attr_accessable...

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7 Comments

niels what you think @students[0] contents?
Well, it's elegant enough. Thanks @neils!
Just checked this out, but this wouldn't work. There's no flag method on @students.
@berto77, you would have to create an attribute for flag. You can't just assign it on the fly.
After a moment of consideration, I think my solution, although it should work, violates some best practices: it introduces view logic in the model and in the controller. So, use at your own risk! :)
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I'm not sure if I understand your problem correctly, but I'm going to take a shot at it.

Assuming you're using @students as the instance variable for your list, you can pass the list of students to your partial like so:

<%= render 'students', :locals => {:students => @students} %>

Inside the students/_students, you can loop through the list and determine their position by using each_with_index:

<% students.each_with_index do |student, index| %>
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Hi @Terence thanks for your answer. I'm trying to avoid doing a loop in my views. I'm trying to use the best practice like so: render :@students where the actual partial that gets rendered is students/_student for each record in @students; without the obvious loop. See here: rails-bestpractices.com/posts/61-simplify-render-in-views
@berto77, you said in your question that you want the collection to be present in your partial, but you're trying to avoid doing a loop in your views? Those two statements are contradictory to each other. What exactly are you trying to accomplish? Also, the point of doing render 'students', :locals => {:students => @students} (which isn't necessarily bad practice according to your link) instead of render @students is to use each_with_index. Doing the second option will only result to using each.
you can proceed with your 'render @students" call if you want. just take note that you magically have a student_counter helper available for you in your partial when you do that. now in your partial, you can compare the student_counter with @students.size and set your link_to's :location=>'first/last' via helper or decorator
I wasn't aware of that helper. Thanks. TIL. You should probably post that as an answer.
@keikun17 Thanks! This makes total sense. I'll try it out after 5 p.m :)

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