Rails 5 create multiple child objects using parent object by the use of nested attributes

Question

So, I'm fairly new to Rails and I'm stuck due to my model's complexity.

I have a Developer model, a Township model and a Project model and their contents are as follows:-

Developer.rb

Class Developer < ApplicationRecord
  has_many :townships,
  has_many :projects, through: :townships

  accepts_nested_attributes_for :township
end

Township.rb

Class Township < ApplicationRecord
  belongs_to :developer
  has_many :projects

  accepts_nested_attributes_for :project
end

Project.rb

Class Project < ApplicationRecord
  belongs_to :township

end

I want to create projects such as follows:-

project = Developer.create(
          {
           name: 'Lodha',
           township_attributes: [
            {
             name: 'Palava', 
             project_attributes: [
              {
               name: 'Central Park'
              },
              {
               name: 'Golden Tomorrow'
              }
            ]}
          ]})

Any ideas as to how can I accomplish this? I also need to understand the strong params whitelisting required in the DeveloperController.

ok, but the relations are: 1) Developer is many-to-many with Project or 2) Developer has-many Township hast-many Project — rogelio
– rogelio, Commented Mar 5, 2017 at 5:05
Developer and township have a one to many and township and projects have a one to many mapping. So, developer and projects should have a one to many mapping as well through township. — Ashishkumar Pandey
– Ashishkumar Pandey, Commented Mar 5, 2017 at 5:08
is "a one to many" a has_many association? or a has_one AND a has_many association in the same model at same time? — rogelio
– rogelio, Commented Mar 5, 2017 at 5:16

theBrezilien · Accepted Answer · 2017-03-05 07:29:58Z

3

I don't know of a way for you to create it in one line (plus it would be less readable) , but you can do this with rails using similar code to below:

def create
  developer = Developer.new(name: 'Loha')
  township = developer.townships.build({ name: 'Palava' })
    # for this part I don't know what your form looks like or what the 
    # params look like but the idea here is to loop through the project params like so
  params[:projects].each do |key, value|
    township.projects.build(name: value)
  end

  if developer.save
    redirect_to #or do something else
  end
end

Saving the developer will save all of the other things with the correct foreign keys assuming you have them set up correctly. Just pay attention to the format of your params to make sure you're looping through it correctly.

edited Mar 5, 2017 at 7:29

answered Mar 5, 2017 at 6:45

theBrezilien

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3 Comments

Ashishkumar Pandey Over a year ago

Thank you for your guidance. Yes, I understand your approach very well. I still do believe there must be a way to accomplish this in a go as the mapping is very simple and consistent. Regarding the model inheritance, Rails 5 now automatically generates an abstract class called ApplicationRecord which inherits ActiveRecord::Base so that no patching is to be done to customise or extend ActiveRecord's functionality.

theBrezilien Over a year ago

Awesome, thanks for the correction, I didn't know that.

Ashishkumar Pandey Over a year ago

Sure, always a pleasure. 😁👍

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