rqrcode_png rails controller - Passing by parameter the string contained in the bank

How do I pass the value that is in the field "codigo" of table "mesas" to the space below "VALOR_STRING_BANCO" ?

How do I pass the value that is in the "codigo" field of the "mesas" table to the space below " VALOR_STRING_BANCO" ."

CONTROLLER

class MesasController < ApplicationController
          before_action :set_mesa, only: [:show, :edit, :update, :destroy]

        require 'rqrcode_png'

          # GET /mesas
          # GET /mesas.json
          def index
            @mesas = Mesa.all


            # Preciso colocar a string que está no banco dentro deste campo abaixo, "VALOR_STRING_BANCO".
            @qr = RQRCode::QRCode.new("VALOR_STRING_BANCO").to_img.resize(90, 90).to_data_url
          end

          # GET /mesas/1
          # GET /mesas/1.json
          def show
          end

          # GET /mesas/new
          def new
            @mesa = Mesa.new
          end

          # GET /mesas/1/edit
          def edit
          end

          # POST /mesas
          # POST /mesas.json
          def create
            @mesa = Mesa.new(mesa_params)

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

          # PATCH/PUT /mesas/1
          # PATCH/PUT /mesas/1.json
          def update
            respond_to do |format|
              if @mesa.update(mesa_params)
                format.html { redirect_to @mesa, notice: 'Mesa was successfully updated.' }
                format.json { render :show, status: :ok, location: @mesa }
              else
                format.html { render :edit }
                format.json { render json: @mesa.errors, status: :unprocessable_entity }
              end
            end
          end

          # DELETE /mesas/1
          # DELETE /mesas/1.json
          def destroy
            @mesa.destroy
            respond_to do |format|
              format.html { redirect_to mesas_url, notice: 'Mesa was successfully destroyed.' }
              format.json { head :no_content }
            end
          end

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

            # Never trust parameters from the scary internet, only allow the white list through.
            def mesa_params
              params.require(:mesa).permit(:cadeiras, :codigo, :observacao, :reservada)
            end
        end

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