Partner() expected, got String() - ruby

Question

I have a course model and there is a many to many relationship with category, i am using a multi select on my form to get an array of objects, A course also can have a partner and the user can select this from a single select, but when i want to save to the database I call the params then I get a string instead of an object. not to sure how I can solve this
<%= form_for #course do |f| %>
<section class="new_course">
<div class="row collapse">
<div class="medium-5 small-centered column">
<%= f.label :course_title, :class=>"custom-prefix-class" %>
<%= f.text_field :title, :autofocus => true, :class=>"custom-input-class" %>
</div>
</div>
<div class="row collapse">
<div class="medium-5 small-centered column">
<%= f.label :start_date, :class=>"custom-prefix-class" %>
<%= f.text_field :start_date, :class=>"custom-input-class" %>
</div>
</div>
<div class="row">
<div class="medium-5 column with_chosen">
<%= f.collection_select :categories,
Category.all ,:id,:name,
{ include_blank: true},
{ class: 'chosen-select', :multiple=>true, :data => { :placeholder => ' ' }}
%>
</div>
</div>
<div class="row">
<div class="medium-5 column">
<%= f.collection_select :partner,
Partner.all.collect, :id,:name ,
{ include_blank: true },
{ class: 'chosen-select', :multiple=>false, :data => { :placeholder => ' Brand Partner' }}
%>
</div>
</div>
In my controller
def create
#course = Course.new(course_params)
end
if #course.save
render :action=>'new'
end
end
private
def course_params
params.require(:course).permit(:title, :start_date,:duration,:partner,:categories => [])
end
//rails server output
Started POST "/courses" for 127.0.0.1 at 2014-02-07 16:45:28 +0200
Processing by CoursesController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"sKhAF2X6VOXTxZC9Pt51RFQfZSKdzXVWji6x4uwg+rI=", "course"=>{"title"=>"Marketing ", "start_date"=>"14-02-2014", "categories"=>["", "1", "2"], "partner"=>"1", "duration"=>"2-weeks"}, "commit"=>"Add new course"}
Completed 500 Internal Server Error in 3ms
ActiveRecord::AssociationTypeMismatch (Partner(#70274068591140) expected, got String(#70274066607160)):
app/controllers/courses_controller.rb:24:in `create'

Answer 1

try this out:-
it seems as that partner is a model and course has_one partner, so you
have to assign partner class object instead of id as string
actually as you can see in in question above value of
params[:course][:partner]
=> "1"
is a string now if you try to do something like #course.partner
= '1' it will raise an error like above, as on left hand side we have parter association and right and side a string.
just do this
def course_params
params.require(:course).permit(:title, :start_date,:duration,:partner,:categories => [])
if params[:course][:partner].present?
params[:course][:partner] = Partner.find params[:course][:partner]
end
end