so i have 2 models:

```
create_table "holders", :force => true do |t|
 t.string   "faceid"
 t.integer  "badges_id"
 t.datetime "created_at", :null => false
 t.datetime "updated_at", :null => false
end
add_index "holders", ["badges_id"], :name => "index_holders_on_badges_id"

create_table "badges", :force => true do |t|
 t.string   "name"
 t.text     "description"
 t.datetime "created_at",  :null => false
 t.datetime "updated_at",  :null => false
end

```

i need 2 things:

1. to get all the badges of a certain faceid holder
2. to get all the holders of a certain badge.

i know its really noobs question but until now i didnt work with references so i dont really understood from the literature how to make the connection.