Maybe/app/controllers/transactions_controller.rb

class TransactionsController < ApplicationController
  before_action :authenticate_user!
  before_action :set_transaction, only: %i[ show edit update destroy ]

  def index
    @transactions = Current.family.transactions
  end

  def show
  end

  def new
    @transaction = Transaction.new
  end

  def edit
  end

  def create
    account = Current.family.accounts.find(params[:transaction][:account_id])

    @transaction = account.transactions.build(transaction_params)

    respond_to do |format|
      if @transaction.save
        format.html { redirect_to transaction_url(@transaction), notice: "Transaction was successfully created." }
      else
        format.html { render :new, status: :unprocessable_entity }
      end
    end
  end

  def update
    respond_to do |format|
      if @transaction.update(transaction_params)
        format.html { redirect_to transaction_url(@transaction), notice: "Transaction was successfully updated." }
      else
        format.html { render :edit, status: :unprocessable_entity }
      end
    end
  end

  def destroy
    @transaction.destroy!

    respond_to do |format|
      format.html { redirect_to transactions_url, notice: "Transaction was successfully destroyed." }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_transaction
      @transaction = Transaction.find(params[:id])
    end

    # Only allow a list of trusted parameters through.
    def transaction_params
      params.require(:transaction).permit(:name, :date, :amount, :currency)
    end
end