Question

My models

I’m trying to create a form for an Annotation. This annotation belongs to a Map, and each annotation should have one Boundary. A map can have many annotations.

I first created the association by letting both Annotation and Map has_one Boundary, but later I switched to using a polymorphic boundary_object. The error was the same regardless.

has_one :boundary, :as => :boundary_object         # <= Map
has_one :boundary, :as => :boundary_object         # <= Annotation
belongs_to :boundary_object, :polymorphic => true  # <= Boundary

---

Views and Controller

Here’s the thing: First I used Boundary.new to create a new boundary object here, since I didn’t have a pre-set annotation object, since the form can be submitted multiple times.

maps/show.html.erb

<%= form_for([@map, Annotation.new], :remote => true ) do |f| %>
    <%= f.text_area :body, :cols => 80, :rows => 10, :style => "width: 500px" %>
    <%= f.fields_for Boundary.new do |b| %>
      <%= b.text_field :ne_x, :style => "display:none" %>
      <%= b.text_field :ne_y, :style => "display:none" %>
      <%= b.text_field :sw_x, :style => "display:none" %>
      <%= b.text_field :sw_y, :style => "display:none" %>
    <% end %>
<% end %>

I could use f.fields_for :boundary too, if I have this in the maps_controller.rb:

@annotation = @map.annotations.build
@annotation.boundary = Boundary.new

But the result is still the same.

annotations_controller.rb

def create
  @annotation = Annotation.new(params[:annotation])
  respond_to do |format|
    if @annotation.save
      format.js { }
  end
end

---

The Error

When submitting that form, this results in the following error at the first line in the create method.

ActiveRecord::AssociationTypeMismatch (Boundary(#2158793660) expected, got ActiveSupport::HashWithIndifferentAccess(#2165684420))

Obviously, the form works without the whole boundary thing. These are the parameters submitted:

{
  "utf8"=>"✓",
  "authenticity_token"=>"6GDF6aDc6GMR3CMP+QzWKZW9IV9gSxfdkxipfg39q7U=",
  "annotation"=>
  {
    "body"=>"foo bar",
    "boundary"=>
    {
      "ne_x"=>"11312", 
      "ne_y"=>"5919", 
      "sw_x"=>"6176", 
      "sw_y"=>"1871"
    }
  }, 
 "map_id"=>"1"
}

What do I have to do to be able to create the Boundary object for this annotation right away?

Answer 1

According to your associations:

First, you need to build a new boundary object (see here for more info):

def show
  @map = ...
  @annotation = @map.annotations.build
  @boundary = @annotation.build_boundary # build new boundary
end

Second, you need to edit your view:

<%= form_for([@map, @annotation], :remote => true ) do |f| %>
  <%= f.text_area :body, :cols => 80, :rows => 10, :style => "width: 500px" %>
  <%= f.fields_for :boundary do |b| %>
    ...
  <% end %>
<% end %>

Third, check that you have accepts_nested_attributes_for for your Boundary in the Annotation model.

accepts_nested_attributes_for :boundary

The form will then look like this – note that the name of the association needs _attributes:

<input … name="annotation[boundary_attributes][ne_x]" … />