NoMethodError at /members undefined method `friend_id' for nil:NilClass - ruby-on-rails

Question

Now I am trying to add "follow button" on my users' index page.
My goal is like... when users push the button once, the message beside the button turns "following". And he or she push it again, the message turns "not following". Default message is "not following".
And then I wrote the codes below but got an error message.Could you tell me how to solve this problem?
NoMethodError at /members undefined method `friend_id' for nil:NilClass
☆index.html.erb(members_controller)
<table class="table">
<tr>
<th>写真</th>
<th>名前</th>
<th>分野</th>
<th>場所</th>
<th>経験</th>
<th>Follow</th>
<%# if Member.find(session[:user_id]).admin %>
<%# end %>
</tr>
<% #members.each do |member| %>
<tr>
<td>
<% if member.provider %>
<%=image_tag member.image ,:size=>'30x30'%>
<% elsif member.avatar_file_name %>
<%= image_tag member.avatar.url(:thumb), :width =>'30px', :height =>'30px' %>
<% else %>
<%= image_tag "love.png", :size=>'30x30' %>
<% end %>
</td>
<td>
<%= member.name %>
<% if member.provider == "facebook" %>
<a target="_blank" href="http://www.facebook.com/<%=member.uid %>"> <%=image_tag "fb.png" ,:size=>'20x20'%> </a>
<% elsif member.provider == "twitter" %>
<a target="_blank" href="http://www.twitter.com/<%=member.name %>"> <%=image_tag "twitter.png" ,:size=>'20x20'%> </a>
<% end %>
</td>
<td><%= member.field %></td>
<td>
<% if member.url.present? %>
<%=link_to member.place ,member.url ,:target=>["_blank"] %>
<% else %>
<%= member.place %>
<% end %>
</td>
<td><%= member.experience %></td>
<td>
<div class="onoff">
<% unless session[:user_id] == member.id %>
<% if #isFr.friend_id == member.id %>
<%= link_to'off', {:controller => 'members', :action => 'index', :id =>
member.id}, class: "btn btn-midium btn-primary"%><br/>
※following
<% else %>
<%= link_to'on', {:controller => 'members', :action => 'index', :id =>
member.id}, class: "btn btn-midium btn-primary"%><br/>
※not following
<% end %>
<% end %>
</div>
<%#= member.friends.count %>
</td>
<% if Member.find(session[:user_id]).admin %>
<td><%= link_to 'Destroy', member, method: :delete, data: { confirm: 'Are you sure?' } %></td>
<% end %>
</tr>
<% end %>
</table>
☆members_controller
def index
if !checklogin? then return end
#members = Member.where("id >=1").order("created_at desc").paginate(:page => params[:page], :per_page => 10).scoped
if params[:name].present?
#members = #members.where("name like ?" , "%" + params[:name] + "%")
end
if Friend.where(:member_id => session[:user_id], :friend_id => params[:id]).exists? then
Friend.where(:member_id => session[:user_id], :friend_id => params[:id]).each do |f|
f.destroy
end
else
Friend.new({:member_id => session[:user_id], :friend_id =>params[:id].to_i}).save
end
#members.each do |m|
#isFr = Friend.where(:member_id => session[:user_id], :friend_id =>
m.id ).first
end
respond_to do |format|
format.html # index.html.erb
format.json
end
end
☆sessions_controller #session[:user_id]
auth = request.env["omniauth.auth"]
member = Member.find_by_provider_and_uid(auth["provider"], auth["uid"])
session[:user_id] = member.id

Answer 1

Below query must be returning blank AR
#members = Member.where("id >=1")
.order("created_at desc")
.paginate(:page => params[:page], :per_page => 10).scoped
And #isFr is eventually resulting in nil
#members.each do |m|
#isFr = Friend.where(:member_id => session[:user_id], :friend_id =>
m.id ).first
end
Just a word of refactor you can do
Friend.where(:member_id => session[:user_id], :friend_id => #members.map(&:id)) .limit(1)
But would be better if you think on the associations between your models. That way it will optimize with join queries

Answer 2

Thanks to those who gave me hints, I made it with the code below.
☆index.html.erb(members_controller)
<td>
<div class="onoff">
<% unless session[:user_id] == member.id %>
<% if #Frids.include? member.id%>
<%= link_to'Off', {:controller => 'members', :action => 'index', :id =>
member.id}, class: "btn btn-midium btn-warning"%><br/>
※既follow
<% else %>
<%= link_to'On', {:controller => 'members', :action => 'index', :id =>
member.id}, class: "btn btn-midium btn-primary"%><br/>
※未follow
<% end %>
<% end %>
</div>
<%#= member.friends.count %>
</td>
☆members_controller
def index
if !checklogin? then return end
#members = Member.where("id >=1").order("created_at desc").paginate(:page => params[:page], :per_page => 10).scoped
if Friend.where(:member_id => session[:user_id], :friend_id => params[:id]).exists? then
Friend.where(:member_id => session[:user_id], :friend_id => params[:id]).each do |f|
f.destroy
end
else
Friend.new({:member_id => session[:user_id], :friend_id =>params[:id].to_i}).save
end
#Frids =Friend.where(:member_id => session[:user_id]).map{|x| x.friend_id}
respond_to do |format|
format.html # index.html.erb
format.json
end
end

Answer 3

The problem here is that the instance var #isFr in your index action returns nil. That means the code Friend.where(:member_id => session[:user_id], :friend_id => m.id ).first is returning nil.
You could do <% if #isFr.try(:friend_id) == member.id %> in your members#index view so that that you won't get the NoMethodError.
There's something wrong with the below code I found in your index action:
#members.each do |m|
#isFr = Friend.where(:member_id => session[:user_id], :friend_id => m.id ).first
end
The problem with the code above is that #isFr will only retain value of the last element in #members array. It's better to add a method in the Member model for that behavior like this:
#in app/models/friend.rb
scope :get_member_id, ->(member, user_id) { where(:member_id => user_id, :friend_id => member.id ).first.try(:friend_id) }
Then use it in your view like:
<% unless session[:user_id] == member.id %> # below this line of code
<% if Friend.get_member_id(member, session[:user_id]) == member.id %>
Hope this helps!