Nested attributes not saving in database? Does not display values - Ruby on Rails

I have a nested attribute and I can display values, but it is not saving into database why?

I have a model review and I want to nest attribute comments

review migration file

class CreateReviews < ActiveRecord::Migration
  def change
    create_table :reviews do |t|
      t.belongs_to :reviewable, polymorphic: true
      t.timestamps
    end
    add_index :reviews, [:reviewable_id, :reviewable_type]

  end
end

review model

class Review < ActiveRecord::Base
  attr_accessible :rating, :user_id, :comments_attributes, :service
  has_many :comments, as: :commentable
  belongs_to :user
  belongs_to :reviewable, polymorphic: true

  accepts_nested_attributes_for :comments

end

comments migration file

class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.text :content
      t.belongs_to :commentable, polymorphic: true
      t.integer :user_id
      t.timestamps
    end
    add_index :comments, [:commentable_id, :commentable_type]
  end
end

comment model

class Comment < ActiveRecord::Base
  attr_accessible :content, :user_id
  belongs_to :commentable, polymorphic: true
  belongs_to :user
  belongs_to :review
end

This is the form

<%= form_for [@reviewable, @review], :html => {:multipart => true} do |f| %>

  <%= f.fields_for :comments, @review.comments.build do |field| %>
    <%= field.label "Comment" %></div>
    <%= field.text_field :content %>
  <% end %>

  <%= f.submit %>
<% end %>

It displays the fields, but how come when I save, it doesn't save?

I tried to display like this:

<%= @review.comments %>

Here's my review controller

  def new
    @review = @reviewable.reviews.new
    @review.comments.build
  end

Thanks for your help!

EDIT:

Review controller: create method

  def create
    @review = @reviewable.reviews.new(params[:review])
    @review.user = current_user
    if @review.save
      redirect_to @reviewable, notice: "review created."
    else
      render :new
    end
  end