can select relection from relation db

app/controllers/desktop/co_authors_controller.rb

@@ -18,6 +18,7 @@ class Desktop::CoAuthorsController < ApplicationController
 
   def new
     @co_author = CoAuthor.new
+    @co_author_relations = CoAuthorRelation.all
 
     respond_to do |format|
       format.html { render :layout => false}

app/models/user/co_author_relation.rb

@@ -5,4 +5,6 @@ class CoAuthorRelation
   field :relation, localize: true
 
   has_and_belongs_to_many :co_authors
+
+  validates :relation, presence: true
 end

app/models/user/user.rb

@@ -3,7 +3,7 @@ class User
   include Mongoid::Document
   include Mongoid::Timestamps
 
-  devise :database_authenticatable, :recoverable, :rememberable, :trackable, :registerable, :timeoutable
+  devise :database_authenticatable, :recoverable, :rememberable, :trackable, :registerable, :validatable, :timeoutable
   
   mount_uploader :avatar, AvatarUploader
   

app/views/desktop/co_authors/_form.html.erb

@@ -15,19 +15,14 @@
   <%= f.text_field :email %>
   </li>
 
-  <li class="s_grid_row">
+
   <%= f.label :type%><br />
   <select name="co_author[type]" id="" class="s_grid s_grid_4">
     <%= options_for_select(
-      [["朋友","朋友"],
-       ["學生","摯友"],
-       ["老師","老師"],
-       ["摯友","摯友"],
-       ["親戚","親戚"],
-       ["同事","同事"],
-       ["共同作者","共同作者"]
-    ])
-  %>
+      @co_author_relations.map do |relation|
+        [relation.relation, relation.id]
+      end
+    )%>
   </select>
   </li>
 </ul>