Render :collection calling partial with phantom object?

Rails
1

I have two models with a straightforward has_many / belongs_to
relationship:

class Premise < ActiveRecord::Base
has_many :metered_services, :dependent => :destroy
…
end

class MeteredService < ActiveRecord::Base
belongs_to :premise
…
end

and nested routes to match:

Demo::Application.routes.draw do
devise_for :users
resources :premises do
resources :metered_services
end
…
end

I want to show/edit the metered services on the same page as premise
edit page, so my views/premises/edit.html.erb file has this line:

<% Rails.logger.debug("== #{@premise.address} has
#{@premise.metered_services.count} metered services") %>
<%= render :partial => “metered_services/metered_service”, :collection
=> @premise.metered_services %>

and my stubbed views/metered_services/_metered_service.html.erb is just
this:

<% Rails.logger.debug("== _metered_service: metered_service =
#{metered_service.inspect}") %>

So here’s what’s weird: With a newly created premise – before I’ve
added any metered services – the _metered_service.html.erb partial gets
called with a metered service object whose ID is nil and whose
premise_id field is filled in with the owning premise. But there should
be ZERO metered services, not one. The console will show something
like:

== 1800 Pennsylvania Avenue has 0 metered services
MeteredService Load (0.2ms) SELECT “metered_services”.* FROM
“metered_services” WHERE (“metered_services”.premise_id = 48)
== metered_service = #<MeteredService id: nil, premise_id: 48, … >

Is this a special “feature” of render … :collection? I can always
filter out metered_services with nil ids in the partial, but that seems
really odd. Am I doing something wrong?

  • ff
2

maybe you have to add nested_attributes

3

On Mar 1, 12:54am, Fearless F. [email protected] wrote:

this:

== 1800 Pennsylvania Avenue has 0 metered services
MeteredService Load (0.2ms) SELECT “metered_services”.* FROM
“metered_services” WHERE (“metered_services”.premise_id = 48)
== metered_service = #<MeteredService id: nil, premise_id: 48, … >

Is this a special “feature” of render … :collection? I can always
filter out metered_services with nil ids in the partial, but that seems
really odd. Am I doing something wrong?

That sounds like you’ve got an unsaved metered_service somewhere (eg
by doing premise.metered_services.build)

Fred

4

actually i have done somethign similiar these is my code

<%= @todo.todostags.build %>
<%= form_for(@todo) do |f| %>

<%= f.submit %>
here the todo model class Todo < ActiveRecord::Base has_many :todostags, :foreign_key =>"todos_id" , :primary_key =>'id' accepts_nested_attributes_for :todostags, :allow_destroy => :true, :reject_if => proc { |attrs| attrs.all? {|k,v| v.blank?}} end

class Todostag < ActiveRecord::Base

belongs_to :tag , :foreign_key =>“tags_id”
belongs_to :todo , :foreign_key =>“todos_id”

end

5

Frederick C. wrote in post #984616:

That sounds like you’ve got an unsaved metered_service somewhere (eg
by doing premise.metered_services.build)
Fred

Yep, that’s true. I based my code on the canonical blog posts /
comments example, so in views/premises/edit.html.erb, I wrote:

<%= form_for([@premise,
@premise.metered_services.build(:account_identifier => “gas”)]) do |f|
%>
<%= f.submit “add gas account” %>
<% end %>

… and it clearly calls build() whenever it renders the page. But this
leads to two questions:

  • (Curiosity:) How did render(… :collection) know about the newly
    created metered_service without an ID? I know that
    premise.metered_services.build will create a new record, but it appears
    that the new record doesn’t appear on the premises.metered_services list
    until it’s saved.

  • (Necessity:) Assume the user is looking at
    views/premises/edit.html.erb. I want a button that says “add
    metered_service to the current premise”. What’s the right way to do
    that? (Clearly, I haven’t made friends with form_for() just yet.)

TIA.

  • ff
6

On Mar 1, 4:49pm, Fearless F. [email protected] wrote:

  • (Curiosity:) How did render(… :collection) know about the newly
    created metered_service without an ID? I know that
    premise.metered_services.build will create a new record, but it appears
    that the new record doesn’t appear on the premises.metered_services list
    until it’s saved.

build adds the record to the in memory collection

  • (Necessity:) Assume the user is looking at
    views/premises/edit.html.erb. I want a button that says “add
    metered_service to the current premise”. What’s the right way to do
    that? (Clearly, I haven’t made friends with form_for() just yet.)

There’s a railscast covering one possible approach:

Fred

7

Frederick C. wrote in post #984876:

There’s a railscast covering one possible approach:
#197 Nested Model Form Part 2 - RailsCasts

@Lorenzo: Looks good. Thanks.

@Frederick: I’m beginning to believe that “if you can imagine it, Ryan
Bates has already coded it.” Thanks for the pointer. I should start
watching the railscasts regularly.

  • ff