Getting fields_for to work with has_many relations

问题:

I'm having trouble generating a nested model form.

Here are my models:

class Workout < ActiveRecord::Base
    has_many :scores
    has_many :users, :through => :scores
    accepts_nested_attributes_for :scores
end

class Score < ActiveRecord::Base
    belongs_to :user
    belongs_to :workout
end

class User < ActiveRecord::Base
    has_many :scores
    has_many :workout, :through => :scores
end

In the Workout controller, here's what I have for the new action:

def new
    @workout = Workout.new
    3.times { @workout.scores.build }

    respond_to do |format|
        format.html # new.html.erb
        format.json { render json: @wod }
    end
end

However, in the form, when I try fields_for, I don't get anything:

<% f.fields_for :scores do |builder| %>
    <p>
        <%= builder.label :score %><br />
        <%= builder.text_field :score %>
    </p>
<% end %>

What am I doing wrong?

回答1:

It turns out in Rails 3, I need to use <%= fields_for ... %> instead of <% fields_for ... %>.

回答2:

Try adding the following to your Workout model:

attr_accessible :scores_attributes

accepts_nested_attributes_for :scores

If you want to make sure that a score doesn't get built unless is it valid, and that is can be destroyed through the relationship you can expand to:

attr_accessible :scores_attributes

accepts_nested_attributes_for :scores, reject_if: proc { |a| a[:field].blank? }, allow_destroy: true
validates_associated :scores

Just switch :field with a relevant field that is required for a score to be created.