CODEWITHSUNDEEP
ruby-on-railsruby
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Reputation: 3594

Self-reference in a Rails Model

Let's say I have two models: User and 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

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.

Upvotes: 0

Views: 421

Answers (3)

techvineet
techvineet

Reputation: 5111

Assuming that User model has

has_many :points

you can do like this in User model

def total_points
    points.sum(:amount)
end

Upvotes: 3

James Lim
James Lim

Reputation: 13054

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

For example,

person.points.sum('amount')

or

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

Upvotes: 0

Peter Alfvin
Peter Alfvin

Reputation: 29389

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

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.

Upvotes: 0

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