CODEWITHSUNDEEP
ruby-on-railsdatabase
Artur Haddad
Artur Haddad

Reputation: 1529

How to decrease db attribute value over time with Rails?

I'm creating a credit-based application, where the user puts credit in his account and the credit decreases over time based on user's active services.

For example:

I realize that I can use cron jobs to decrease the account balance, but it's gonna make a lot of requests to database and I am sure there must be better ways to do that.

How can I do it?

Upvotes: 0

Views: 160

Answers (1)

Md. Farhan Memon
Md. Farhan Memon

Reputation: 6121

One way to achieve this is using a column and a callback e.g.

You will need to add a column say last_deducted_on as date then in the show action of account_balance you can have a before_action like

before_action :deduct_amount_if_applicable, only: :show

private

def deduct_amount_if_applicable
  if current_user.deduction_applicable?
    amt = (Date.today - account.last_deducted_on).to_i * amount_to_be_deducted
    account.update_attribute(:total, (account.total - amt))
    # update column with today's date
  end
end

Although it will work, I suggest to use scheduler as it is a scheduled job and needs to be done every day, there are ways to reduce queries e.g. using update_all, etc. depending on use case but still the better option. In case if you have transaction history and you show date of transaction, above method will piss of user if he will open his account days later and suddenly huge amount is deducted.

Upvotes: 1

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