Filter in list page associated with other model

Using Rails 4 and Ruby 2.2, I have Subject list page where I need to add the filter for subject's name, username, active and books associated with the subject. All the three model i.e

Subject, Book and User

are associated as below:

user.rb

class User < ActiveRecord::Base
  has_many :subjects, dependent: :destroy
  has_many :books, dependent: :destroy
end

book.rb

class Book < ActiveRecord::Base
    belongs_to :subject, dependent: :destroy
    belongs_to :user, dependent: :destroy
    has_many :images, dependent: :destroy
end

subject.rb

class Subject < ActiveRecord::Base
  belongs_to :user
  has_many :books
  validates :name, presence: true,
                length: { minimum: 3 }


  def self.names(name)
    subject = all
    subject = subject.where("name LIKE ?", "%#{name}%")
    return subject
  end


  def self.actives(active)
    subject = all
    subject = subject.where("active = ?", "%#{active}%")
    return subject
  end


  def self.usernames(username)
    user = all
    user = user.where("username LIKE ?", "%#{username}%")
    return user
  end

end

Now I am trying to make filter on the subject list page with the following column

1. Username(Drop Down from User table)
2. Subject name(text field from subject table)
3. Active(Drop Down from subject table)
4. Has books (Radio button, association with books)

I have my index for subject as follows:

subjects_controller.rb

def index

   @subjects = Subject.page(params[:page]).per(10)
   @users = User.all
   @subjects = @subjects.names(params[:name]) if params[:name].present?
   @subjects = @subjects.actives(params[:active]) if params[:active].present?
   @users = @users.usernames(params[:username]) if params[:username].present?
end

and my

index.html.erb

as:

<h1>Listing Subjects</h1>
<%= link_to 'New Subject', new_subject_path %>

<%= form_tag subjects_path, :method=> "get" do %>

  <%= label_tag :username, "Username" %>
  <%= select_tag :username, options_from_collection_for_select(User.all, "id", "username", username) %>

  <%= label_tag :name, "Subject Name"%>
  <%= text_field_tag :name %>


  <%= label_tag :active, "Active" %>
  <%= select_tag :active, options_for_select([['Active', true], ['Inactive', false]]) %>


  <%= submit_tag "submit" %>
  <%= link_to "Clear Search", request.path, class:"cancel-button" %>
<% end %>


<div id="subjects"><%= render "index" %></div>

<%= paginate @subjects %><br>

Questions:

1. How can I have username column associated with each book in filter list
2. How to make filter list for has books or not as radio button?
3. How the active for subject(boolean datatype) list will work ?

Let me know if I need to provide more details