title: Polymorphic association, creating a record
body: <p>I'm trying to seed a GroupItem record but I'm not providing the correct data into the create method. </p>
  
  <p>Here's what I tried in the rails console:</p>
  
  <pre><code>irb(main):055:0&gt; group = Group.first
    Group Load (0.2ms)  SELECT  "groups".* FROM "groups" ORDER BY "groups"."id" ASC LIMIT ?  [["LIMIT", 1]]
  =&gt; #&lt;Group id: 1, groupable_type: "Legislator", name: "Cool Peeps", created_at: "2017-02-23 01:13:21", updated_at: "2017-02-23 01:13:21"&gt;
  
  irb(main):056:0&gt; person = Role.first
    Role Load (0.2ms)  SELECT  "roles".* FROM "roles" ORDER BY "roles"."role_id" ASC LIMIT ?  [["LIMIT", 1]]
  =&gt; #&lt;Role role_id: 100, caucus: nil, congress_numbers: "[106]", current: false, description: "Representative for Wisconsin's 2nd congressional d...", district: 2, enddate: "2001-01-03", address: nil, contact_form: nil, fax: nil, office: nil, rss_url: nil, how: nil, leadership_title: nil, party: "Democrat", person_id: 400013, phone: nil, role_type: "representative", role_type_label: "Representative", senator_class: nil, senator_rank: nil, startdate: "1999-01-06", state: "WI", title: "Rep.", title_long: "Representative", website: "", created_at: "2017-02-23 01:11:08", updated_at: "2017-02-23 01:11:08"&gt;
  
  irb(main):059:0&gt; GroupItem.create(group_id: group.id, groupable_type: group.groupable_type, groupable_id: person.id)
     (0.1ms)  begin transaction
    Legislator Load (0.1ms)  SELECT  "legislators".* FROM "legislators" WHERE "legislators"."id" = ? LIMIT ?  [["id", 100], ["LIMIT", 1]]
    Group Load (0.1ms)  SELECT  "groups".* FROM "groups" WHERE "groups"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
     (0.1ms)  rollback transaction
  =&gt; #&lt;GroupItem id: nil, group_id: 1, groupable_type: "Legislator", groupable_id: 100, created_at: nil, updated_at: nil&gt;
  </code></pre>
  
  <p>here is the set-up:</p>
  
  <pre><code>class Group &lt; ApplicationRecord
      has_many :group_items
  end
  
  class GroupItem &lt; ApplicationRecord
      belongs_to :groupable, polymorphic: true
      belongs_to :group 
  end
  
  class Role &lt; ApplicationRecord
      belongs_to :person, foreign_key: :person_id
      has_many :group_items, as: :groupable
      #....
  end
  
  # migrations...
  
  
  class CreateGroups &lt; ActiveRecord::Migration[5.0]
    def change
      create_table :groups do |t|
        t.string :name
  
        t.timestamps
      end
    end
  end
  
  class CreateGroupItems &lt; ActiveRecord::Migration[5.0]
    def change
      create_table :group_items do |t|
        t.integer :group_id
        t.references :groupable, polymorphic: true, index: true
  
        t.timestamps
      end
    end
  end
  
  class CreateRoles &lt; ActiveRecord::Migration[5.0]
    def change
      create_table :roles, :id =&gt; false do |t|
           t.primary_key :role_id
           #...
  
           t.timestamps
  
      end
    end
  end
  </code></pre>
  
  <p>It must be a problem with the associations, this is my first venture into polymorphic so I probably messed up something there.</p>