Rails - filtering multiple tables with scope - ruby-on-rails

Question

I'm doing an online word learning project and i want to making a search feature where you can filter word by lessons, words and learning status (learned/unlearned). Filter by lessons and words are done. I'm stuck at the last filter condition. I'm using scope and the params for learn status just can't seems to get to the scope, the "words" table and "user_words" table won't join (i tried with these two tables first).
Here are my tables:
create_table "users" do |t|
t.string "username"
end
create_table "words" do |t|
t.string "name"
t.integer "lesson_id"
end
create_table "user_words" do |t|
t.integer "user_id"
t.integer "word_id"
t.boolean "status"
end
My models:
class User < ApplicationRecord
has_many :user_words
end
class Word < ApplicationRecord
has_many :user_words
scope :order_name_asc, -> {order name: :asc}
scope :search_prefix, -> prefix {where "name like ?", "#{prefix}%"}
scope :search_lesson, -> lesson_id {
where("lesson_id = ?", lesson_id) if lesson_id.present?}
# Is the problem here?
scope :search_learned, -> (learned) do
joins(:user_words).where("user_words.status = ?",
learned[:user_word_status].to_i) if learned[:user_word_status]
end
end
class UserWord < ApplicationRecord
belongs_to :user
belongs_to :word
end
My controller
class StaticPagesController < ApplicationController
before_action :load_lessons, only: :home
before_action :load_user_words, only: :home
def home
#words = Word.search_learned(learned: params[:learned]) #or the problem's here
.search_lesson(params[:lesson_id])
.search_prefix(params[:prefix]).order_name_asc
.paginate page: params[:page]
end
end
And the view:
# Lesson filter option:
<%= select_tag :lesson_id,
grouped_options_for_select(#categories.map {|category|
[category.name,category.lessons.map {|lesson| [lesson.name,
lesson.id]}]}),
include_blank: t(".all_lessons"), class: "btn btn-primary" %>
# Learning status filter option (is the problem here?):
<%= select_tag :learned,
options_for_select(#user_words.map(&:status)),
include_blank: t(".learned"), class: "btn btn-secondary" %>
# Text input fied, submit button and the word list:
<%= text_field_tag :prefix, params[:prefix],
placeholder: t(".search"), class: "form-control" %>
<%= submit_tag t(".search"), name: nil, class: "btn btn-success" %>
<% #words.each do |word| %>
<%= link_to word.name, "#" %>
<% end %>