json - How does rails parse POST request parameters? -

i working on application send post request rails server parameters stored in json format. let's application routes request create function on cats_controller. cat model has 3 fields :name, :hunger, :mood. each cat has_many kittens. kitten model has 2 fields :cat_id (referring cat owns it, because kitten belongs_to cat) , :cute. every time create cat on application want single call, call /cats.json app post request. parameters stored in json format , include following fields {name:"",hunger:"", mood:"",cute:""}. controller takes these params creates new cat, , creates new kitten assigned cat using cat.kittens.build(). kitten needs use last parameter sent "mood:" created properly.

now question this, when print params variable controller following hash: {name:"", hunger:"", mood:"", cute:"", cat:{name:"", hunger:"", mood:""}}. why happen? how rails parse post request params , take me

{name:"",hunger:"", mood:"",cute:""} {name:"", hunger:"", mood:"", cute:"", cat:{name:"", hunger:"", mood:""}}

how "cat" hash generated, when, , rules follow?

then followup question be, since rails 4 forces whitelist parameters before use them. doing:

params.require(:cat).permit(:name,:hunger,:mood)

how permit :cute value?

you'll best reading on http - difference between , post.

---

it's not rails sends request, it's plain old html.

the difference you're looking @ how server picks post params, considering get params passed through url...

note query strings (name/value pairs) sent in url of get request:

note query strings (name/value pairs) sent in http message body of post request

thus, base level answer question need append post params message body of request. best example know of how jquery ajax:

$.ajax({    url: ...,    data: {your: key, value: pairs} }); 

---

to answer other questions, here's structure should use:

#app/models/cat.rb class cat < activerecord::base    #columns id | name | mood | created_at | updated_at    has_and_belongs_to_many :kittens           class_name: "cat",            join_table: :kittens,            foreign_key: :cat_id,            association_foreign_key: :kitten_id    alias_attribute :born, :created_at #-> allows call @cat.born end  #kittens table #columns cat_id | kitten_id 

you can read self join here: rails: self join scheme has_and_belongs_to_many?

this should give ability create cat, , have him/her assigned kitten of cat:

#app/controllers/cats_controller.rb class catscontroller < applicationcontroller    def new       @cat = cat.new    end    def create       @cat = cat.new cat_params       @cat.save    end     private     def cat_params       params.require(:cat).permit(:name, :mood, :kittens)    end end 

this give ability have following:

#app/views/cats/new.html.erb <%= form_for @cat |f| %>    <%= f.text_field :name %>    <%= f.text_field :mood %>    <%= f.collection_select :kittens, cat.all, :id, :name %>    <%= f.submit %> <% end %> 

this allow call:

@cat = cat.find params[:id] @cat.kittens.each |kitten|      kitten.mood #-> "cute"