Error when passing in nil value on Rails object - ruby-on-rails

Question

I have an app where a user has a portfolio. A portfolio can have many positions and each position can have many movements.
My portfolio show page is built like this:
<p>
<strong>Name:</strong>
<%= #portfolio.name %>
</p>
<h1>Positions</h1>
<div class = 'table'>
<table>
<thead>
<tr>
<th>Name</th>
<th>Quantity</th>
<th>Stock</th>
<th colspan="3"></th>
</tr>
</thead>
<tbody id = "positions">
<%= render #positions %>
</tbody>
</table>
</div>
<h3>New Position</h3>
<%= render 'positions/form' %>
<%= link_to 'Edit', edit_portfolio_path(#portfolio) %> |
<%= link_to 'Back', portfolios_path %>
My position partial is built:
<tr>
<td class="col-md-1"><%= position.name %></td>
<td class="col-md-1"><%= position.quantity %></td>
<td class="col-md-1"><%= position.ticker %></td>
<td>
<%= form_for [#portfolio, position, #movement] do |f| %>
<div id = "movement-errors">
<% if #movement.errors.any? %>
<%= render 'shared/error_messages', object: #movement %>
<% end %>
</div>
<div class="field">
<%= f.label :quantity %>
<%= f.number_field :quantity, class: 'form-control' %>
</div>
<div class="actions">
<%= f.submit class: 'btn btn-primary' %>
</div>
<% end %>
</td>
</tr>
And my shared errors partial is:
<% if object.errors.any? %>
<div id = "error_explanation">
<div class = "alert alert-danger">
The form contains <%= pluralize(object.errors.count, "error") %>.
</div>
<ul>
<% object.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
When I submit a nil value on a movement form, I want the errors to pop up and tell the user the message. I have validations checking for presence of quantity.
class Movement < ApplicationRecord
belongs_to :position
validates :quantity, presence: true
And my controller movements#create action looks like
class MovementsController < ApplicationController
before_action :load_portfolio_and_position
def create
#movement = Movement.new(movement_params)
#movement.position_id = #position.id
#movement.update_price
#movement.date = DateTime.now
#movement.trade ='buy'
respond_to do |format|
if #movement.save
#position.update_attribute(:quantity, (#movement.quantity + #position.quantity))
format.html { redirect_to #portfolio, notice: 'Movement was successfully created.' }
format.js
else
format.html { render template: 'portfolios/show' }
format.json { render json: #movement.errors, status: :unprocessable_entity }
format.js
end
end
end
As it stands right now, when I submit an empty form, I get this error using the better_errors gem:
'nil' is not an ActiveModel-compatible object. It must implement :to_partial_path.
And the render #positions line is highlighted from my portfolio show page. I thought I was implementing a partial path. Is my syntax wrong?

Answer 1

When passing an object, needs to be assigned like this.
<%= render partial: 'shared/error_messages', locals: {object: #movement} %>
http://guides.rubyonrails.org/layouts_and_rendering.html#passing-local-variables

Answer 2

When you pass an object to a partial using the object: attribute, then the partial references that object by the name of the partial
e.g.
When you call
<%= render 'shared/error_messages', object: #movement %>
the shared/error_messages partial will have a local variable error_messages that references #movement
When I am only passing one object to a partial I like to use 'as'
e.g.
<%= render 'shared/error_messages', object: #movement , as: :movement %>
That lets you specify the name of the local variable. If I'm passing multiple objects, I'd use the method #7urkm3n described.