Nested Attributes With JSON Rails One to Many

Question

I'm figuring a problem with a nested_attribute.

team.rb:

class Team < ApplicationRecord
  has_many :players, dependent: :destroy
  accepts_nested_attributes_for :players, allow_destroy: true
end

console output:

Processing by TeamsController#create as JSON
  Parameters: {"team"=>{"id"=>nil, "name"=>"testes",
  "players_attributes"=>[{"id"=>nil, "name"=>"dadada", "_destroy"=>false, "team_id"=>nil}]}}
Unpermitted parameter: id

So, i'm ignoring team_id in controller for create and sending it as null same to player_id. What rails is getting in controller after permit is:

team: {name:'testes team', players_attributes: [{ name: 'testes'}]}

In my opinion (prob my mistake) rails should feed this relation in exactly this way. I tested it removing the nested attribute id and team_id but doesn't works.

Rails return:

bodyText: "{"players.team":["must exist"]}

controller:

def create
  @team = Team.create(team_params)

  @team.players.each do |player|
    player.team_id = 1
  end

  respond_to do |format|
    if @team.save
      format.html { redirect_to @team, notice: 'Team was successfully created.' }
      format.json { render :show,  status: :created, location: @team }
    else
      format.html { render :new }
      format.json { render json: @team.errors, status: :unprocessable_entity }
    end
  end
end

def team_params
  params.require(:team).permit(:name, players_attributes: [:name, :positions, :_destroy])
end

gambiarra:

@team.players.each do |player|
  player.team_id = 1
end

If i do this to the nested attribute BEFORE save team it works, team 1 must exists for it to work. If i save only the team and after create the relation it DOESN'T works either, only if I set the "gambiarra" solution.

How to solve this relation? As mentioned, my controller is filtering for only attributes for nested data. If i submit with HTML, works fine, if i use a JSON as nested objects, it doesn't work unless i force the relation to find a team_id for my player before save and so on, rails will save and commit the right player as is expected to do without a team_id in my player.

Answer 1

The structure of the params you are sending is incorrect, rails expects something like this in order to work with nested attributes:

{
  "computer": {
    "speakers_attributes": {
      "0": {
        "power": "1"
      }
    }
  }
}

Notice three things:

1. computer: null was removed; you don't need to specify computer attribute since its value will be set with the id of the new computer to be created.

2. "0": was added; because of the has_many :speakers associations, you can create more than one Speaker (you will use 1: { ... }, 2: { ... }, and so on).

3. speaker: was changed to speakers_attributes; that's the way rails recognizes nested attributes values.

Now that the parameters had been set correctly, you need to do two more things:

1. Confirm that your associations are set correctly

   class Computer < ApplicationRecord
     has_many :speakers, dependent: :destroy
     accepts_nested_attributes_for :speakers, allow_destroy: true
   end
   
   class Speaker < ApplicationRecord
     belongs_to :computer
   end
   

2. Properly setup your controller

   class ComputersController < ApplicationController
     def new
       @computer = Computer.new
       @computer.speakers.build
     end
   
     def create
       @computer = Computer.create(computer_params)
   
       if @computer.save
         # handle success
       else
         # handle error
       end
     end
   
     # other actions
   
     private
     def computer_params
       params.require(:computer).permit(speakers_attributes: [:power])
     end
   end
   

Here @computer.speakers.build is neessary only if you will be creating nested forms using form helpers.