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Accepted
Hector Hernandez
Asked: 2020-09-03 18:05:03 +0800 CST 2020-09-03 18:05:03 +0800 CST

Getting the records of an association in a collection in Rails

  • 772

Cheers! I am trying to get the municipalities of an association in a collection, however I am having difficulties, the municipalities are an association between companies and municipalities, therefore, I would like the collection to print the municipalities associated with the companies that publish those jobs, to To make it simpler, place the current association:

Municipality.rb
has_many :enterprises

Enterprise.rb
belongs_to :muncipality
has_many :jobs

Job.rb
belongs_to :enterprise

If job was directly associated with Municipality I could easily get it like this, using a scope, however I want to take advantage of the companies, my code here:

job.rb

scope :municipality, -> (municipality_id) { where(municipality_id: municipality_id) }

jobs_controller.rb

  def index
    if params[:municipality_id].present?
      @jobs = Job.municipality(params[:municipality_id]).paginate(:page => params[:page], :per_page => 9)      
    else
      @jobs = Job.all.paginate(:page => params[:page], :per_page => 9)
    end
  end

index.html.erb

<%= form_tag({ controller: :jobs, action: :index }, { method: :get }) do %>
  <div class="input-group no-margin">
    <%= select_tag(:municipality_id, options_from_collection_for_select(Municipality.all, :id, :name), { :include_blank => "Todos los municipios", class: "input-group-field" }) %>
    <div class="input-group-button">
      <%= button_tag( :class => "button secondary", name: nil ) do %>
        <i class="fa fa-search" aria-hidden="true"></i>
      <% end %>
    </div>
  </div>
<% end %>
ruby-on-rails

1 Answers

  1. Best Answer

    The fact that there is no direct association between Joband Municipalitydoes not imply that it cannot be used municipality_idwith the model Job, you simply have to do a JOIN with the model Enterprise, which will give you access to the municipality through enterprises.municipality_id.

    Considering the above, the scopeen Jobwould look like this:

    scope :municipality, -> (municipality_id) { 
  joins(:enterprise).where("enterprises.municipality_id = ?", municipality_id)
}

    Of course, since you're building the where, you could omit the table name enterprises, since the column municipality_idis only found in that table; for instance:

    scope :municipality, -> (municipality_id) { 
  joins(:enterprise).where("municipality_id = ?", municipality_id)
}

    It is important to note that you cannot use something like

    joins(:enterprise).where(municipality_id: municipality_id)

    since ActiveRecord will automatically add the table jobsto municipality_id(ie jobs.municipality.id) and the query will return an error.

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