form

<%= f.fields_for :incomes do |income| %>
<%= income.label :name %>
<%= income.text_field :name %>
<%= income.label :amount %>
<%= income.text_field :amount %>
<% end %>

gistfile1.txt

ActionController::UnpermittedParameters in ProjectionsController#update
found unpermitted parameters: incomes


Parameters:

{"utf8"=>"✓",
 "_method"=>"patch",
 "authenticity_token"=>"XwA325J64foUZ6I33rNe2Ec4pRqAfHxxW711CBz/jws=",
 "projection"=>{"name"=>"help",
 "incomes"=>{"name"=>"adfaf",
 "amount"=>"323"}},
 "commit"=>"Update Projection",
 "id"=>"6"}

income.rb

class Income < ActiveRecord::Base

  has_many :income_projections
  has_many :projections, :through => :income_projections

  accepts_nested_attributes_for :income_projections

end

income_projections.rb

income_projection.rb
class IncomeProjection < ActiveRecord::Base

belongs_to :income
belongs_to :projection

end

Projection.rb

class Projection < ActiveRecord::Base

has_many :income_projections
has_many :incomes, :through => :income_projections

accepts_nested_attributes_for :income_projections

def update(post_params)

...

projections_controller

  def edit
        @projection = Projection.find(params[:id])
        @incomes = @projection.incomes

  end
  
  ...
    def update
    respond_to do |format|
      if @projection.update(projection_params)
        format.html { redirect_to @projection, notice: 'Projection was successfully updated.' }
        format.json { render :show, status: :ok, location: @projection }
      else
        format.html { render :edit }
        format.json { render json: @projection.errors, status: :unprocessable_entity }
      end
    end
  end


    def projection_params
      params.require(:projection).permit(:name,
        :incomes,
        income_projections_attributes: [:id,:projection_id, :amount, :name, '_destroy']

)