<%= f.text_field :user_name, autofocus: true, class: "form-control login-field",placeholder: "ユーザネーム",id: "login-name" %>
      </div>

<%= f.text_field :user_name, autofocus: true, class: "form-control login-field",placeholder: "ユーザネーム",id: "login-name" %>
      </div>

validates :user_name, presence: true, uniqueness: true


 def self.from_omniauth(auth)
     where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
     user.provider = auth.provider
     user.uid      = auth.uid
     user.name     = auth.info.name
     user.email    = auth.info.email
     user.password = Devise.friendly_token[0,20]
    end
 end

 def self.new_with_session(params, session)
   super.tap do |user|
      if data = session["devise.facebook_data"] && session["devise.facebook_data"]["extra"]["raw_info"]
      user.email = data["email"] if user.email.blank?
     end
   end
 end

 def self.current_user
    Thread.current[:current_user]
 end

 def password_required?
    super && provider.blank?
 end

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController


def facebook
    # You need to implement the method below in your model (e.g. app/models/user.rb)
    @user = User.from_omniauth(request.env["omniauth.auth"])

    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication #this will throw if @user is not activated
      set_flash_message(:notice, :success, :kind => "Facebook") if is_navigational_format?
    else
      session["devise.facebook_data"] = request.env["omniauth.auth"]
      redirect_to new_user_registration_url
    end
  end
end

<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
    <div class="login-form">
      <p>新規登録</p>

      <div class="form-group">
        <%= link_to user_omniauth_authorize_path(:facebook) do%>
            <div class="btn-sm btn-block btn-social btn-facebook">
              <i class="fa fa-facebook"></i> Facebookで登録
            </div>
        <% end %>
      </div>

      <div class="form-group">
        <label class="login-field-icon fui-mail" for="user_name"></label>
        <%= f.text_field :user_name, autofocus: true, class: "form-control login-field",placeholder: "ユーザネーム",id: "login-name" %>
      </div>

      <% if f.object.password_required? %>
          <div class="form-group">
            <label class="login-field-icon fui-mail" for="email"></label>
            <%= f.email_field :email, autofocus: true, class: "form-control login-field",placeholder: "Email",id: "login-name" %>
          </div>

          <div class="form-group">
            <label class="login-field-icon fui-lock" for="login-pass"></label>
            <%= f.password_field :password, autocomplete: "off", class: "form-control login-field",placeholder: "Password",id: "login-pass" %>
          </div>


          <div class="form-group">
            <label class="login-field-icon fui-lock" for="login-pass"></label>
            <%= f.password_field :password_confirmation, autocomplete: "off", class: "form-control login-field",placeholder: "Password確認用",id: "login-pass" %>

          </div>
          <p class="palette-paragraph">半角英数字8文字以上</p>
      <% end %>
      <br>

      <div class="form-group text-center">
        <%= f.submit "登録する", class: 'btn btn-embossed btn-sm btn-block  btn-warning ' %>
      </div>
    </div>
<% end %>