associations - Rails - how to show attribute of an associated model -

i trying make app in rails 4.

i asked related question , got clear answer. seems can't understand how take logic , apply elsewhere.

rails how show attributes parent object

i have user model, profile model projects model , universities model.

associations are:

profile belongs university profile belongs user university has many profiles university has many projects projects habtm user projects belong universities 

in projects controller, define @creator follows:

def create     logger.debug "xxx create project"     #authorise @project     @project = project.new(project_params)     @project.creator_id = current_user.id     @project.users << current_user     respond_to |format|       if @project.save          format.html { redirect_to @project }         format.json { render action: 'show', status: :created, location: @project }       else         format.html { render action: 'new' }         format.json { render json: @project.errors, status: :unprocessable_entity }       end     end   end 

i try define creator_profile this:

def show     #authorise @project      @project = project.find(params[:id])     @creator = user.find(@project.creator_id)     @creator_profile = @creator.profile    end 

in uni table, have attributes called logo , name. use avatar uploader in have logo defined (that's why have 2 .logo below).

in projects, show, want display university project creator belongs to.

i've tried this:

<%= image_tag(@creator_profile.university.logo.logo) %>          <div class="generaltext"><%= @creator_profile.university.name %> </div> 

i result: undefined method `logo' nil:nilclass

based on link problem above

<%= image_tag(creator_profile.university.logo.logo) %>              <div class="generaltext"><%= creator_profile.university.name %> </div> 

i result:

undefined local variable or method `creator_profile' #<#<class:0x007f998f17ad88>:0x007f998d1ce318> 

i'm not sure understood detailed explanations given in answer previous question. if first version right, don't understand explanation @ all. if second version right, why error message come up?

im wondering if problem arises out of there not being association between university , user? hoping, based on user created project, find uni creator belongs to.

that's why tried:

<%= image_tag(creator_profile.project.university.logo.logo) %>                  <div class="generaltext"><%= creator_profile.project.university.name %> </div> 

i error:

undefined method `project' #<profile:0x007f998ada41b8> 

it seems can't understand how take logic , apply elsewhere.

i don't think appreciate how activerecord associations work in rails. i'll explain further down page.

---

your associations cause of problem.

setting complicated associations tricky - it's best keep data separate possible.

here's how i'd construct models / associations:

#app/models/university_student.rb class universitystudent < activerecord::base    belongs_to :university    belongs_to :student, class_name: "user" #-> student_id end  #app/models/user.rb class user < activerecord::base    has_many :placements, class_name: "universitystudent", foreign_key: :student_id #-> user.placements    has_many :universities, through: :placements #-> user.universities     has_and_belongs_to_many :projects #-> user.projects     has_one :profile #-> user.profile (avatar etc)     has_many :created_projects, class_name: "project", foreign_key: :creator_id end  #app/models/profile.rb class profile < activerecord::base    belongs_to :user #-> store avatar here. can used across entire app end   #app/models/university.rb class university < activerecord::base    has_many :projects    has_many :students, class_name: "universitystudent" #-> university.students end  #app/models/project.rb class project < activerecord::base    belongs_to :university    belongs_to :creator, class_name: "user" #-> creator_id     has_and_belongs_to_many :users     delegate :profile, to: :creator, prefix: true #-> @project.creator_profile end 

this allows following:

def create    @project = curent_user.created_projects.new project_params    @project.users << current_user 

because associations associate data, you'll able following:

def show     @project = project.find params[:id]     #@creator_profile = @project.creator.profile     @creator_profile = @project.creator_profile #-> if use delegate method outlined in models end 

--

in projects, show, want display university project creator belongs to.

#app/controllers/projects_controller.rb class projectscontroller < applicationcontroller    def show       #@project = project.find params[:id]       @project = current_user.created_projects.find params[:id]    end end  #app/views/projects/show.html.erb <%= @project.creator.universities.first %> 

my code above allows multiple universities. thinking it, should limited one, i'll leave now, maybe change later.

in uni table, have attributes called logo , name. use avatar uploader in have logo defined (that's why have 2 .logo below).

don't use 2 logo method, it's antipattern (explained below)

---

the fix two-fold:

firstly, make sure you're calling @creator_profile.university following:

<%= @creator_profile.university %>  

if works, means have problem .logo.logo (detailed below), if doesn't, means you've not defined @creator_profile or university association correctly.

secondly, need ensure have correct controller/view setup.

the problem many people - beginners - don't understand way rails works controllers & views. need appreciate each time render view, only data has access define in corresponding controller action...

#app/controllers/projects_controller.rb class projectscontroller < applicationcontroller     def show         @project = project.find params[:id]         @creator_profile = @project.creator_profile     end end  #app/views/projects/show.html.erb <%= content_tag :div, @creator_profile.universities.first.name, class: "generaltext" %> 

---

trivia

1. @project.creator_id = current_user.id

this should not have defined.

you should able change foreign_key in association, rails automagically define creator_id you:

#app/models/project.rb class project < activerecord::base     belongs_to :creator, class: "user" #-> foreign_key should :creator_id end  #app/controllers/projects_controller.rb class projectscontroller < applicationcontroller    def create       @project = current_user.created_projects.new project_params #-> populates foreign key automatically. 

--

2. .logo.logo

this antipattern.

calling same method twice bad practice - why doing it?

you either want delegate recursive data you're trying access (such example .creator_profile above), or you'll want restructure functionality.

you want following:

if have delegate assets model, away following:

<%= @creator_profile.university.images.logo %>