has_many through associations - ruby-on-rails

Question

I'm making an online fashion store. I have a Category Model and a Sizes Model. A model can have many sizes. A Size can have many Categories.
Therefore i am using has_many through association. The category model and sizes model will be linked via a table called category_sizes.
I will create a bunch of sizes like XS, Small, Medium. Then I will create a category Lets say Shirt then i can select all the Sizes a Shirt will have. Then click create.
How do i make the sizes appear in my view? I tried for hours.
Category Model
class Category < ActiveRecord::Base
has_ancestry
has_many :items
validates :name, presence: true, length: { maximum: 20 }
has_many :category_sizes
has_many :sizes, through: :category_sizes
end
Sizes Model
class Size < ActiveRecord::Base
validates :title, presence: true, length: { maximum: 15 }
validates :title, uniqueness: true
has_many :category_sizes
has_many :categories, through: :category_sizes
end
category_size model
class CategorySize < ActiveRecord::Base
belongs_to :category
belongs_to :sizes
end
Here is my form.
<div class="container">
<div class=“row”>
<div class="col-md-6 col-md-offset-3">
<div class="panel panel-primary">
<div class="panel-body">
<%= simple_form_for(#category) do |f| %>
<div class="form-inputs">
<%= f.input :name %>
<%= f.association :category_sizes %>
<%= f.collection_select :parent_id, Category.order(:name), :id, :name, {prompt: "Select Parrent ID If Applicable"},include_blank: true %>
<div class="form-actions"><%= f.button :submit %></div>
</div>
<% end %>
</div>
</div>
</div>
</div>
</div>
Schema
ActiveRecord::Schema.define(version: 20150915113019) do
create_table "categories", force: :cascade do |t|
t.string "name"
t.string "ancestry"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "categories", ["ancestry"], name: "index_categories_on_ancestry"
create_table "category_sizes", force: :cascade do |t|
t.integer "category_id"
t.integer "size_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
add_index "category_sizes", ["category_id"], name: "index_category_sizes_on_category_id"
add_index "category_sizes", ["size_id"], name: "index_category_sizes_on_size_id"
create_table "items", force: :cascade do |t|
t.string "title"
t.decimal "price"
t.text "description"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "user_id"
t.string "image_file_name"
t.string "image_content_type"
t.integer "image_file_size"
t.datetime "image_updated_at"
t.integer "category_id"
end
add_index "items", ["user_id", "created_at"], name: "index_items_on_user_id_and_created_at"
add_index "items", ["user_id"], name: "index_items_on_user_id"
create_table "sizes", force: :cascade do |t|
t.text "title"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "taggings", force: :cascade do |t|
t.integer "tag_id"
t.integer "taggable_id"
t.string "taggable_type"
t.integer "tagger_id"
t.string "tagger_type"
t.string "context", limit: 128
t.datetime "created_at"
end
add_index "taggings", ["tag_id", "taggable_id", "taggable_type", "context", "tagger_id", "tagger_type"], name: "taggings_idx", unique: true
add_index "taggings", ["taggable_id", "taggable_type", "context"], name: "index_taggings_on_taggable_id_and_taggable_type_and_context"
create_table "tags", force: :cascade do |t|
t.string "name"
t.integer "taggings_count", default: 0
end
add_index "tags", ["name"], name: "index_tags_on_name", unique: true
create_table "users", force: :cascade do |t|
t.string "username"
t.string "email"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.string "password_digest"
t.string "remember_digest"
t.boolean "admin", default: false
t.string "activation_digest"
t.boolean "activated", default: false
t.datetime "activated_at"
t.string "reset_digest"
t.string ">"
t.datetime "reset_sent_at"
t.string "avatar_file_name"
t.string "avatar_content_type"
t.integer "avatar_file_size"
t.datetime "avatar_updated_at"
t.text "description"
end
add_index "users", ["email"], name: "index_users_on_email", unique: true
end

Answer 1

Did you try something like this?
<%= f.select(:size_id, Size.all.map {|s| [s.title, s.id]}) %>

Answer 2

In your controller define ,
#size_variant_array = #category.sizes
In your view,
<%= select_tag 'size',options_for_select(#size_variant_array.collect{ |pv| [pv.title, pv.id] }) ,:prompt => "Please Select"%>