A filtered index page via ids of has_many through child objects

Question

I have an index page for Jobs. Both Cities and Positions has a has_many :through relationship with jobs.

On the Jobs Index Page, I have a small search form, which I would like to use to filter results by the combination of cities and Positions a user chooses.

This is how it looks so far

Jobs#Index

- provide(:title, 'All Jobs')

.thinstripe_career
  .darken
    .container
      .row
        .span10.offset1
          .jobs_header
            .row
              .span7
                h2 All #{@city.name if @city} #{@position.name if @position} Jobs 
              .span3
                == link_to "Sign up for Job Alerts!", "#", :class => "button"

- if current_user && current_user.admin? 
  == render 'shared/dashboard_header' 

.container
  .row
    .span10.offset1
      .job_search
        == form_tag jobs_path, :method => 'get', :id => "jobs_filter" do
          h2 I'd like jobs in
          .filter_sect
            == select_tag :city_id, options_from_collection_for_select(@cities, "id", "name"), :class => "basic" 
          .filter_sect
            == select_tag :position_id, options_from_collection_for_select(@positions, "id", "name"), :class => "basic"             
          .filter_sect.filter_search
            == submit_tag "Search", :class => "button search_button button_black"

      ul.jobs
        == render @jobs

      == will_paginate

Jobs#Index Controller

  def index     
    @cities = City.all
    @positions = Position.all

    @city = City.find(params[:city_id]) if params[:city_id]
    @position = Position.find(params[:position_id]) if params[:position_id]

    @jobs = Job.paginate(page: params[:page])
  end

I would like to @jobs to be be filtered buy @city or @position.

With the condition that if @city is not present, it only filters by @position, and vice versa. If both are not present, then it simply paginates all jobs. However, all the code I think of is quite long and ridden with if statements, so I think I'm going into the wrong path.

How would I go about filtering @jobs through @city and @position?

Answer 1

You can utilize the fact that conditions in multiple where calls are joined by AND when the query is executed:

@jobs = Job
@jobs = @jobs.includes(:cities).where(cities: { id: @city }) if @city
@jobs = @jobs.where(position_id: @position) if @position
@jobs = @jobs.paginate(page: params[:page], per_page: 5)