Cannot get nested form with a has_one association to work

问题

I have these models:

class User < ActiveRecord::Base
    has_one :city
    accepts_nested_attributes_for :city
end

class City < ActiveRecord::Base
    belongs_to :user
end

This controller action:

   def create
    @user = User.new(params[:user])

    respond_to do |format|
      if @user.save
        format.html { redirect_to(@user, :notice => 'User was successfully created.') }
        format.xml  { render :xml => @user, :status => :created, :location => @user }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @user.errors, :status => :unprocessable_entity }
      end
    end
  end

and this view:

<%= form_for :user,:url => users_path,:method => :post do |f| %>
<%= f.fields_for :city do |b| %>
    <%= b.collection_select :id,City.all,:id,:name %>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

I am trying to allow the user to select a city from the list of already added cities. I am trying to present him a select. The select part it works, but the generated html code for it, looks like this:

<select name="user[city][id]" id="user_city_id">
   <option value="1">One</option>
   <option value="2">Two</option>
</select>

Notice that it's name doesn't have attribute anywhere. So, when I try to save it, I get this error:

City(#37815120) expected, got ActiveSupport::HashWithIndifferentAccess(#32969916)

How can I fix this?

EDIT: there is some progress, I tried to change the fields_for to this:

<%= f.fields_for :city_attributes do |b| %>
    <%= b.collection_select :id,City.all,:id,:name %>
<% end %>

and now, the html seems to generate correctly. But I get this error now:

Couldn't find City with ID=1 for User with ID=

I have no idea what to do next.

EDIT2: overriding the city_attributes= method seems to work:

def city_attributes=(attribs)
    self.city = City.find(attribs[:id])
end

I don't know if it's the way to go, but it seems good.

回答1:

Have a look at this question that seems similar to yours : Rails 3: How does "accepts_nested_attributes_for" work?

Actually, since the Cities already exsit, I think there is no need for nested forms here.

Try Replacing

<%= f.fields_for :city_attributes do |b| %>
    <%= b.collection_select :id,City.all,:id,:name %>
<% end %>

With

<%= f.collection_select :city, City.all,:id,:name %>

Updated afters comments

Could you change your relationship with (and update database scheme accordingly)

class User < ActiveRecord::Base
    belongs_to :city
end

class City < ActiveRecord::Base
    has_many :users
end

And then try using:

<%= f.collection_select :city_id, City.all,:id,:name %>

回答2:

You could also do a

<%= f.collection_select :city_id, City.all, :id, :name %>

in your view and then add virtual attributes to your User model:

class User < ActiveRecord::Base
  ...
  def city_id(c_id)
    update_attribute(:city, City.find(c_id))
  end

  def city_id
    city.id
  end
end

This might not be very clean, since the associated City model is "saved" whenever assigning an ID to some_user.city_id. However, this solution keeps your controller and view nice and clean.

Note: you might also want to account for a blank ID being passed in to the setter method.

回答3:

Try this

<%= f.select(:city_id, City.all.collect {|p| [ p.name, p.id ] }) %>

来源：https://stackoverflow.com/questions/5576895/cannot-get-nested-form-with-a-has-one-association-to-work

标签

ruby-on-rails

nested-forms

has-one