Question

My app uses a :has_many :through association, and I’m having trouble figuring out how to most efficiently load and display data from both ends of the association and the association itself.

Here are my classes:

class Person < ActiveRecord::Base
  has_many :people_ranks
  has_many :ranks, :through => :people_ranks
  has_many :institutions_people
  has_many :institutions, :through => :institutions_people
  belongs_to :school
  belongs_to :department
end
class Institution < ActiveRecord::Base
  has_many :institutions_people
  has_many :people, :through => :institutions_people
end
class InstitutionsPerson < ActiveRecord::Base
  belongs_to :institution
  belongs_to :person
end

and their corresponding models:

    create_table :people, :force => true do |t|
      t.string :name
      t.string :degree
      t.integer :year_grad
      t.integer :year_hired
    end
   create_table :institutions, :force => true do |t|
      t.string :name
      t.integer :ischool
    end
    create_table :institutions_people, :id => false do |t|
      t.integer :institution_id
      t.integer :person_id
      t.string :rel_type
    end

I want to show a person’s institution info with something like @person.year_hired, @person.institution.name, and @person.institution.institutions_people.rel_type (where rel_type is either “graduated” or “hired:), but I know that third part won’t work. Using the following in the show bit in the person_controller:

    @person = Person.find(params[:id], :include => [:school, :department, :institutions_people, :people_ranks, {:institutions_people => :institution}, {:people_ranks => :rank}])

gives me access to @person.institutions and @person.institutions_people, but how do I connect the rel_type attribute from the join to the person-institution relationship? (I’m coming from PHP and now how to build the SQL and loop through it there, but RoR has me stumped.)

I’ve looked for help under “eager loading” and “associations with :has_many :through”, but I get answers about building the associations. My question is really about accessing the association’s data after it exists. My app uses static data, and I’m not worried about the update, destroy, or create methods. Thank you for your help!

Answer 1

The way to access the data is through the institutions_people association. So, you would do something like:

me = Person.first
rel = me.institutions_people.first

And then in the view

<%= rel.rel_type %> from <%= rel.institution.name %>

Alternatively, you can give yourself a full list of institutions along with their info:

me = Person.first

And then in the view:

<% for ip in me.institutions_people %>
  <%= ip.rel_type %> from <%= ip.institution.name %>
<% end %>