Software as a Service (SaaS) = leasing = access to software with an end date.

You are charged to postpone the end date.

From this perspective, a “One-time payment” = subscription with lifetime access.

Minimalistic Database representation:

subscription-uml-1

Example: Spotify subscription

In this case a user can buy a premium subscription for $12,11 for a limited time 1 month to remove adds.

Here’s how it will work:

# user.rb

#  email      :string
#  ends_at    :datetime

def premium_price
  # how much to charge for postponing ends_at
  # always keep money in integer. last 2 digits are cents
  1299.to_i 
end

def premium_interval
  # by how long to postpone the ends_at
  # monthly or yearly or forever
  1.month 
end

def active_subscription?
  ends_at > Time.now
end

def show_annoying_adds?
  # business logic
  unless active_subscription?
end
# charge.rb

# user_id     :integer
# amount      :integer # to track how much was paid at this moment of time

belongs_to :user
# charges_controller.rb

def create
  @charge.amount = current_user.premium_price

  # PAYMENT PROVIDER LOGIC GOES HERE

  if @charge.save
    current_user.update(ends_at: Time.now + current_user.premium_interval)
  end
end

This way whenever a user makes a payment and creates a charge, his subscription ends_at is set to a later date based on premium_interval.

Of course, in this simple example charges are not automatic and the user has to explicitly create a charge.

That’s it! 🤠


The SaaS business model can usually have 2 collection_methods:

  • charge_automatically
  • send_invoice