associations - Rails - How to show attribute of parent object -

i making app rails 4.

i trying understand how work associations , show attributes associated models. i'm struggling grasp concepts.

i have project model , project_invitations model.

the associations are:

projects has many project invitations project invitations belong project 

in project_invitation show, trying display project attributes project creator attributes (stored in user profiles table).

i getting stuck.

in project_invitation show, have:

you're invited participate in <%= project_invitation.project.title %> 

i have tried:

you're invited participate in <%= @project_invitation.project.title %> 

when try ^^ error:

undefined method `title' nil:nilclass 

in project table, have attribute called :title.

i want project invitation show show name of project invitee has been invited.

what's wrong way i've tried it?

my project_invitations controller has following (generated scaffold):

class projectinvitationscontroller < applicationcontroller   before_action :set_project_invitation, only: [:show, :edit, :update, :destroy]    # /project_invitations   # /project_invitations.json   def index     @project_invitations = projectinvitation.all   end    # /project_invitations/1   # /project_invitations/1.json   def show   end    # /project_invitations/new   def new     @project_invitation = projectinvitation.new   end    # /project_invitations/1/edit   def edit   end    # post /project_invitations   # post /project_invitations.json   def create     @project_invitation = projectinvitation.new(project_invitation_params)      respond_to |format|       if @project_invitation.save         format.html { redirect_to @project_invitation, notice: 'project invitation created.' }         format.json { render action: 'show', status: :created, location: @project_invitation }       else         format.html { render action: 'new' }         format.json { render json: @project_invitation.errors, status: :unprocessable_entity }       end     end   end    # patch/put /project_invitations/1   # patch/put /project_invitations/1.json   def update     respond_to |format|       if @project_invitation.update(project_invitation_params)         format.html { redirect_to @project_invitation, notice: 'project invitation updated.' }         format.json { head :no_content }       else         format.html { render action: 'edit' }         format.json { render json: @project_invitation.errors, status: :unprocessable_entity }       end     end   end    # delete /project_invitations/1   # delete /project_invitations/1.json   def destroy     @project_invitation.destroy     respond_to |format|       format.html { redirect_to project_invitations_url }       format.json { head :no_content }     end   end    private     # use callbacks share common setup or constraints between actions.     def set_project_invitation       @project_invitation = projectinvitation.find(params[:id])     end      # never trust parameters scary internet, allow white list through.     def project_invitation_params       if can? :create, project,         params[:project_invitation].permit(:comment, :expiry_date, :draft, :course_credit)       elsif can? :read, projectinvitation         params[:project_invitation].permit(:student_accepted, :sponsor_accepted)       end     end end 

the project_invitation model has:

class projectinvitation < activerecord::base        belongs_to :project       belongs_to :user end 

the project model has:

class project < activerecord::base    include rolemodel    #belongs_to :students, through: :courses, counter_cache: true    has_many :project_questions, dependent: :destroy#, through: :projects   accepts_nested_attributes_for :project_questions    has_one :sweep   accepts_nested_attributes_for :sweep    has_one :educator_project_comment   has_many :project_student_eois   belongs_to :educator   has_many :project_invitations   has_one :video   accepts_nested_attributes_for :video   has_one :finalise, through: :sweep   has_many :observations    has_one :approval_request   belongs_to :industry   belongs_to :course    has_and_belongs_to_many :users   belongs_to :creator, class_name: 'user'   has_many :profiles, through: :industry     mount_uploader :hero_image, avataruploader   mount_uploader :link_to_video_proposal, videouploader end 

in project_invitiatons show page, have:

<div class="containerfluid"> <%= render 'static/deviselinks'%>   <div class="row">     <div class="col-md-10 col-md-offset-1">           <h1 class="header-project" style="margin-bottom:10%">you're invited participate in <%= @project_invitation.project.try(:title) %></h1>     </div>    </div>      <div class="row">         <div class="col-md-6 col-md-offset-1">             <div class="row">                 <div class="col-md-12" style="padding:5%">                      <div class="invitebody">                         <%= @project_invitation.comment %>                     </div>                 </div>             </div>             <div class="row">                 <div class="col-md-8 col-md-offset-2" style="padding:5%">                     <div class="invitebody">                         if you'd participate in project, reply <%= @project_invitation.expiry_date.try(:strftime, '%d %b %y') %>                         <br>                         <%= render 'rsvp' %>                     </div>                 </div>             </div>            </div>            <div class="col-md-3 col-md-offset-1" style="padding: 10%">             <div class="row">                 <div class="col-md-12">                     <% if @creator_profile.image.present? %>                         <%= image_tag (@creator_profile.image.profile) %>                     <% else %>                         <div class="generaltext">image tbc</div>                     <% end %>                 </div>             </div>             <div class="row">                 <div class="col-md-12">                     <%= "#{@creator_profile.title} #{@creator.first_name} #{@creator.last_name}" %>                 </div>             </div>             <div class="row">                 <div class="col-md-12">                 <%= image_tag (@project.hero_image.thumb) %>                 </div>             </div>             <div class="row">                 <div class="col-md-12">                     <%= @project.title %>                 </div>             </div>         </div>     </div>        <div class="formminor">       <%= link_to 'back', project_invitations_path %>     </div> </div> 

i put 'try' before 'title' because having other issues saving new invitation. wanted see if problem. expecting next error of same kind , flagging problem 'comment'. jumped on , raised error as:

undefined method `image' nil:nilclass 

that's strange me because i'm asking if there 1 present. also, code comes after question comment , doesn't seem have problem there.

this bit confusing.

undefined method `title' nil:nilclass

this means variable you're trying access not exist.

ruby treats nil objects nilclass, when call method on type of object, ruby thinks you're trying call method doesn't exist. it's not method issue lack of variable.

---

associations

here's code i'd expect see:

#app/models/project.rb class project < activerecord::base     has_many :invitations end  #app/models/invitation.rb class invitation < activerecord::base    belongs_to :user    belongs_to :project    delegate :title, to: :project, prefix: true #-> prevents "law of demeter" end 

you can read law of demeter here.

i know model projectinvitations; have rule make model names succinct possible - helps clarity throughout app.

this allow call following:

#app/controllers/invitations_controller.rb class invitationscontroller < applicationcontroller    def index       @invitations = invitation.all    end     def new       @invitation = invitation.new    end     def create       @invitation = invitation.new invitation_params       @invitation.save    end     def show       @invitation = invitation.find params[:id]    end     private     def invitation_params        params.require(:invitation).permit(:user,:project)    end end 

---

views (fix)

because haven't explained view you're calling erroneous variable inside, i'll have speculate:

#app/views/invitations/index.html.erb <% @invitations.each |invitation| %>    <%= invitation.project_title %> <% end %>  #app/views/invitations/show.html.erb <%= @invitation.project_title %> 

the key know view you're calling, , @variable have available. guess you're trying call @project_invitations variable in view it's not defined.

---

model

as aside, shouldn't have many associations in 1 model.

you can - there's no rule against - problem specification end creating small functionality 1 single purpose.

the best systems dry (don't repeat yourself) - reuse functionality time , time again.

for example...

has_one :educator_project_comment 

this changed following:

has_many :comments    def educators       type = "educator"    end end 

you'd able have sti table setup comments, type column denoting dependent model you're calling (in case "educator").