Rails 4 - find nested attributes, select certain child

Question

I have and object with a nested model. I am currently getting all the nested objects like so:

@no = Parent.find(params[:parent_id]).children

Now, one of these children has an attribute that identifies them as the favorite. How can I get the favorite child from among the children?

In addition, how can I edit the attributes using fields_for for just that single object in the view/update?

Answer 1

I don't know the name of your attribute that identifies the record as the favorite, but let's say it is a boolean named is_favorite. Considering this abose, the following should work:

children = Parent.find(params[:parent_id]).children
@favorited_children = children.where(is_favorite: true) # return 0..N records! not only 0..1 !

To edit its attributes, you can do as following (you will have to translate it in ERB or HAML, depending on what your app uses):

form_for @favorited_children do |form_builder|
  form_builder.text_field :name
  form_builder.check_box :is_favorite
end 

Hope this helps!

Answer 2

You could also look at using an ActiveRecord Association Extension

This basically works by creating instance methods you can chain onto the child association, like so:

#app/models/parent.rb
Class Parent < ActiveRecord::Base
    has_many :children do
       def favorites
           where(is_favorite: true) #-> to use MrYoshi's example
       end
    end
end

This will allow you to use the following:

@parent = Parent.find params[:id]
@favorites = @parent.children.favorites