具有 has_one - belongs_to 关联的未定义方法

Question

class Activity < ActiveRecord::Base
  belongs_to :user
  belongs_to :contract
  belongs_to :customer
  has_one    :expense
end

class Expense < ActiveRecord::Base
    belongs_to :activity
end

当我尝试在 ExpensesController 中创建一个 Expense 时，我得到 undefined method expense' for nil:NilClass：

if !activity.try(:expense)
        activity.expense.create(ref: @current_date, year: session[:current_year], month: session[:current_month],
                                days:["1", "2"])
end

我想这是正常的，因为服务器正在尝试从 nil.

中调用 expense

问题是原来的代码不是我的。我必须添加 Activity 和 Expenses 之间的关联。我应该怎么做才能创建新的 Expenses?

编辑：这是 ExpensesController

的 show 操作的完整代码

def show
if session[:current_month] == nil && session[:current_year] == nil
  session[:current_month] = params[:month]
  session[:current_year] = params[:year]
else
  if session[:current_month] != params[:month] || session[:current_year] != params[:year] 
    session[:current_month] = params[:month]
    session[:current_year] = params[:year]
  end
end

@calendar, @previous_month, @next_month, @month_name = get_calendar(session[:current_year], session[:current_month])
@current_date = @month_name + " " + session[:current_year]

# If expense does not exist, create one with current month
activity = Activity.where(month: params[:month], year: params[:year]).first
if activity.try(:expense)
  @nb_days = 0
  @calendar.each do |c|
      @nb_days += 1
  end
else
  activity.expense.create(ref: @current_date, year: session[:current_year], month: session[:current_month],
                            days:[""])
end   
@expense = activity.expense
end

Answer 1

如果我没看错的话，你的 activity 变量是空集。我认为问题出在这里：

activity = Activity.where(month: params[:month], year: params[:year]).first

这没有返回任何记录。

具有 has_one - belongs_to 关联的未定义方法

undefined method with has_one - belongs_to assocation

ruby-on-rails

has-one