Rails "follow" relationship controller issues - ruby-on-rails

Question

I am working on an app where users' "projects" can follow "plant" objects from the database. I am getting the following error for the create action in my "Prelationships" controller (Plant Relationships that connect Users' projects to fixed "plant" objects) when I hit "Follow" for any number of plant objects in my app:
"You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]"
I realize this is a big question, and yes, I'm pretty much a newbie. All the migrations should be fine. I appreciate any help--even if it means suggesting a whole new way of tackling this issue.
Here's what my controller, called "Prelationships", looks like:
class PrelationshipsController < ApplicationController
def create
#plant = Plant.find(params[:prelationship][:pfollowed_id])
#project.follow!(#plant)
respond_to do |format|
format.html { redirect_to #project }
format.js
end
end
end
And my "Prelationships" model:
class Prelationship < ActiveRecord::Base
attr_accessible :pfollowed_id
belongs_to :pfollower, :class_name => "Project"
belongs_to :pfollowed, :class_name => "Plant"
validates :pfollower_id, :presence => true
validates :pfollowed_id, :presence => true
end
And my "Projects" model:
class Project < ActiveRecord::Base
attr_accessible :title, :address, :latitude, :longitude, :state
belongs_to :user
has_many :prelationships, :foreign_key => "pfollower_id",
:dependent => :destroy
has_many :pfollowing, :through => :prelationships, :source => :pfollowed
def pfollowing?(pfollowed)
prelationships.find_by_pfollowed_id(pfollowed)
end
def pfollow!(pfollowed)
prelationships.create!(:pfollowed_id => pfollowed.id)
end
end
And my "plant" model:
class Plant < ActiveRecord::Base
has_many :prelationships, :foreign_key => "pfollowed_id",
:class_name => "Prelationship"
has_many :pfollowers, :through => :reverse_prelationships,
:source => :pfollower
end
And, finally, my "_plants_form" partial for the view:
<%= form_for #project.prelationships.build(:pfollowed_id =>
#project_id) do |f| %>
<%= collection_select(:prelationships, :pfollowed_id, Plant.all, :id, :name,
options = {:prompt => "Select your plants"}, :class => "listselect") %>
<div class="actions"><%= f.submit "Pfollow" %></div>
<% end %>
Here's the error from my log:
Started POST "/prelationships" for 127.0.0.1 at 2011-11-20 23:31:57 +0100
Processing by PrelationshipsController#create as HTML
Parameters: {"utf8"=>"✓",
"authenticity_token"=>"NKqa1f0M2yPLQDHbRLnxl3SiwBeTus/1q1hpZjD7hgY=",
"prelationships"=>{"pfollowed_id"=>"5"}, "commit"=>"Pfollow"}
Completed 500 Internal Server Error in 14ms
NoMethodError (You have a nil object when you didn't expect it!
You might have expected an instance of Array.
The error occurred while evaluating nil.[]):
app/controllers/prelationships_controller.rb:4:in `create'
Rendered /Users/mmelone12/.rvm/gems/ruby-1.9.2-p290/gems/actionpack-
3.0.9/lib/action_dispatch/middleware/templates/rescues/_trace.erb (1.4ms)
Rendered /Users/mmelone12/.rvm/gems/ruby-1.9.2-p290/gems/actionpack-
3.0.9/lib/action_dispatch/middleware/templates/rescues/_request_and_response.erb
(30.6ms)
Rendered /Users/mmelone12/.rvm/gems/ruby-1.9.2-p290/gems/actionpack-
3.0.9/lib/action_dispatch/middleware/templates/rescues/diagnostics.erb within
rescues/layout (37.1ms)

Answer 1

Yep. Like Swanand point out, you should initialize #project object inside :create action. Like #project = Project.find(params[:project_id]) if you do not do it with a before_filter.
If you already instantiated #project before, see what happens when you manually try to retrieve #plant object in Rails console Plant.find(1)