Rails - NoMethodError未定义的方法`> ='对于nil：NilClass

Question

我在模型中遇到上述错误。 这是型号代码 -

Booking.rb

    class Booking < ActiveRecord::Base

    belongs_to :event
    belongs_to :user

    validates :quantity, presence: true, numericality: { greater_than: 0 }
    validates :total_amount, presence: true, numericality: { greater_than: 0 }
    validates :event, presence: true, numericality: {greater_than_or_equal_to: 0 }

    before_validation :set_default_values_to_greater_than_or_equal_to_zero

    def set_default_values_to_greater_than_or_equal_to_zero
        self.quantity >= 1
        self.total_amount >= 0  
        self.event.price >= 1    unless self.event.is_free
    end

    def reserve(stripe_token)
        # Don't process this booking if it isn't valid
        self.valid?

        # We can always set this, even for free events because their price will be 0.
        #self.total_amount = booking.quantity * event.price

                # Free events don't need to do anything special
                if event.is_free?
                save!

                # Paid events should charge the customer's card
                else

                    begin
                        self.total_amount = event.price * self.quantity
                        charge = Stripe::Charge.create(
                            amount: total_amount,
                            currency: "gbp",
                            source: stripe_token, 
                            description: "Booking created for amount #{total_amount}")
                        self.stripe_charge_id = charge.id
                        save!
                    rescue Stripe::CardError => e
                    errors.add(:base, e.message)
                    false
                end
            end 
        #end
    end
end

错误代码抛出此行 -

self.quantity >= 1

我相信这是因为此特定列/属性的默认值（或缺少一个）。 在迁移中纠正此问题的正确流程是什么？ 我是否进行了change_column_null迁移或change_column_default？

这是我的表 -

 create_table "bookings", force: :cascade do |t|
    t.integer  "event_id"
    t.integer  "user_id"
    t.string   "stripe_token"
    t.datetime "created_at",       null: false
    t.datetime "updated_at",       null: false
    t.integer  "quantity"
    t.integer  "total_amount"
    t.string   "stripe_charge_id"
  end

很明显，没有为数量设置（也不是total_amount）。 我试图通过下面的before_validation回调和方法来解决这个问题，但它们似乎没有起作用。 我相信迁移是解决这个问题的唯一方法，我是否正确？

这是我的控制器代码，我需要放在这里吗？

bookings_controller.rb

 class BookingsController < ApplicationController

before_action :authenticate_user!

def new
    # booking form
    # I need to find the event that we're making a booking on
    @event = Event.find(params[:event_id])
    # and because the event "has_many :bookings"
    @booking = @event.bookings.new(quantity: params[:quantity])
    # which person is booking the event?
    @booking.user = current_user


end

def create

    # actually process the booking
    @event = Event.find(params[:event_id])
    @booking = @event.bookings.new(booking_params)
    @booking.user = current_user

        if 
            @booking.reserve(booking_params['stripe_token'])
            flash[:success] = "Your place on our event has been booked"
            redirect_to event_path(@event)
        else
            flash[:error] = "Booking unsuccessful"
            render "new"
        end
end


private

def booking_params
    params.require(:booking).permit(:stripe_token, :quantity, :event_id, :stripe_charge_id, :total_amount)
end

结束

Answer 1

如果set_default_values_to_greater_than_or_equal_to_zero尝试设置这些属性的默认值，则更改>= to =因为>=是一个将返回true或false的求值运算符。 如果你走这条路，我建议把它作为私人方法。

如果你想要进行迁移，要在数据库级别设置默认值（我赞成在验证回调之前），

change_column_default(:bookings, :quantity, 1)

要么

change_column :bookings, :quantity, :integer, :default => 1

看到：

更改列默认值

改变专栏

如change_column_default页面注释中所述，更改列是执行此操作的首选方法