Rails "has_many" association: "collection=" doesn't work as expected - ruby-on-rails

Question

Invoice has many invoice entries:
class Invoice < ActiveRecord::Base
has_many :invoice_entries, :autosave => true, :dependent => :destroy
validates_presence_of :date
end
class InvoiceEntry < ActiveRecord::Base
belongs_to :invoice
validates_presence_of :description
end
Assume we have a single invoice in the database:
id: 1
date: '2013-06-16'
and it has two invoice entries:
id: 10 id: 11
invoice_id: 1 invoice_id: 1
description: 'do A' description: 'do C'
Now, I have the new invoice entries:
id: 10
description: 'do B' description: 'do D'
(Existing invoice entry (New invoice entry
with updated description) without id)
I would like the invoice to have only these new invoice entries (this means that invoice entry with id=11 should be deleted).
invoice.invoice_entries = new_invoice_entries seems to do half of the work. It removes the invoice entry with id=11, creates a new invoice entry with description 'Do D', but it doesn't update the description of invoice entry with id=10 from 'Do A' to 'Do B'. I guess that when Rails sees an existing id in new_invoice_entries, it totally ignores it. Is that true? If yes, what is the rationale behind this?
My full code is below. How would you fix this issue? (I use Rails 4, in case it simplifies the code.)
# PATCH/PUT /api/invoices/5
def update
#invoice = Invoice.find(params[:id])
errors = []
# Invoice entries
invoice_entries_params = params[:invoice_entries] || []
invoice_entries = []
for invoice_entry_params in invoice_entries_params
if invoice_entry_params[:id].nil?
invoice_entry = InvoiceEntry.new(invoice_entry_params)
errors << invoice_entry.errors.messages.values if not invoice_entry.valid?
else
invoice_entry = InvoiceEntry.find_by_id(invoice_entry_params[:id])
if invoice_entry.nil?
errors << "Couldn't find invoice entry with id = #{invoice_entry_params[:id]}"
else
invoice_entry.assign_attributes(invoice_entry_params)
errors << invoice_entry.errors.messages.values if not invoice_entry.valid?
end
end
invoice_entries << invoice_entry
end
# Invoice
#invoice.assign_attributes(date: params[:date])
errors << #invoice.errors.messages.values if not #invoice.valid?
if errors.empty?
# Save everything
#invoice.invoice_entries = invoice_entries
#invoice.save
head :no_content
else
render json: errors.flatten, status: :unprocessable_entity
end
end

Answer 1

To change not only the association but also the attributes of the associated objects, you have to use accepts_nested_attributes_for:
class Invoice < ActiveRecord::Base
has_many :invoice_entries, :autosave => true, :dependent => :destroy
validates_presence_of :date
accepts_nested_attributes_for :invoice_entries, allow_destroy: true
end
There's a railscast episode 196 on how to build dynamic nested forms using nested_attributes.
Addendum:
accepts_nested_attributes_for expects attributes for the nested models in a nested hash, i.e.:
invoice_params={"date" => '2013-06-16',
"invoice_entries_attributes" => [
{"description" => "do A"},
{"description" => "do B"}]
}
invoice= Invoice.new(invoice_params)
invoice.save
the save saves invoice and two invoice_items.
Now
invoice=Invoice.find(1)
invoice_params={
"invoice_entries_attributes" => [
{"description" => "do A"},
{"description" => "do C"}]
}
invoice.update_attributes(invoice_params)
deletes the item do B and adds the item do C.
form_fields can be used to create forms that result in exaclty that kind of nested hashes.
For details see the railscast.

Answer 2

Try using accepts_nested_attributes_for. This would clean up a lot of your code! Here is a example:
class Invoice < ActiveRecord::Base
has_many :invoice_entries, :dependent => :destroy
validates_presence_of :date
attr_accessible :invoice_entries_attributes
accepts_nested_attributes_for :invoice_entries, :allow_destroy => true
end
In the view can you then use fields_for (simple_fields_for with simple form, and semantic_fields_for with formtastic if you use one of these gems).
<%= form_for #invoice do |invoice_form| %>
<%= invoice_form.fields_for :invoice_entries do |invoice_entry_form| %>
<%= invoice_entry_form.text_field :description %>
<%= invoice_entry_form.check_box :_destroy %>
<% end %>
<% end %>
In you controller can you now refactor down to the basics:
# PATCH/PUT /api/invoices/5
def update
#invoice = Invoice.find(params[:id])
if #invoice.update_attributes(params[:invoice]) # This also saves all associated invoice entries, and destroy all that is marked for destruction.
head :no_content
else
render json: #invoice.errors.flatten, status: :unprocessable_entity
end
end
You can read more about accepts_nested_attributes_for here: http://api.rubyonrails.org/classes/ActiveRecord/NestedAttributes/ClassMethods.html
Or you can watch this railscast about nested models: http://railscasts.com/episodes/196-nested-model-form-revised