Rails模型中的自引用

Let's say I have two models: User and Point.

假设我有两个模型：User和Point。

Point belongs_to the user. Point has an 'amount'. I want to define a method in the Point model that will return the user's total points. I'd like to call it in such a manner: user.points.total

Point belongs_to用户。 Point有一个'金额'。我想在Point模型中定义一个返回用户总分的方法。我想以这样的方式调用它：user.points.total

I just don't know how to define the method in the Point model in such a way that I don't have to pass it the User's ID. I'd imagine there is a simple way to do this, but my Googlefu is failing me.

我只是不知道如何在Point模型中定义方法，以便我不必将其传递给用户的ID。我想有一个简单的方法可以做到这一点，但我的Googlefu让我失望了。

3 个解决方案

#1

Assuming that User model has

假设用户模型有

has_many :points

you can do like this in User model

你可以在用户模型中这样做

def total_points
    points.sum(:amount)
end

#2

Given that you want the method defined in the Point model, you'd want to use:

鉴于您需要Point模型中定义的方法，您需要使用：

class Point
  def total
    user.points.sum(:amount)
  end
end

You can then get the total points for the user associated with a given point by invoking point.total. You can't get total points through User.points.total because User is a class and doesn't refer to a particular user.

然后，您可以通过调用point.total来获取与给定点关联的用户的总分数。您无法通过User.points.total获得总分，因为User是一个类，并且不引用特定用户。

#3

Consider using #sum, which uses SQL sum to do an aggregation.

考虑使用#sum，它使用SQL sum进行聚合。

For example,

例如，

person.points.sum('amount')

要么

# inside User.rb
def total
  points.sum('amount')
end

#1