Rails: How to manage associations between two tables syncing data?

Question

I will be having two Rails applications, one is full fledged and other one a stripped down one. Both of these applications have their own database and they will communicate to each other using APIs.

I have two models like this (in both the apps):

class Scan < ApplicationRecord
  has_many :background_processes, dependent: :destroy      
end

class BackgroundProcess < ApplicationRecord
  belongs_to :scan
end

Any record saved triggers the sync across the database using web services. Now when the sync across two applications will happen, the dependent model (in this case background_processes) will have different scan_id.

How should we handle the associations in case of data sync?

Answer 1

I'd recommend using another indexed column on the scan model where you could store another id or token that you can use to query the scan record. Maybe call it sync_id or something.

If you take this route, you don't have to worry about the differing scan_ids on the background process records. Just be sure to send the background process records with the scan's JSON body. (Assuming your using JSON as the format for your APIs.)

Here's the general idea.... You would make sure that your sending API service sends the entire scan record with dependent background processes. The receiving API service, then needs to use that scan records sync_id to query for an existing scan record and update it. You'll need to use some sort of unique identifier on the background process records as well to ensure you're not creating duplicates. If need be, create a sync_id on the background processes as well. If the scan record with that id doesn't exist, then create it and the dependent background processes.

Essentially, the sending service's API POST request might look something like this:

{
id: 1,
sync_id: "sometoken"
... # other record columns
background_process: [
  {
  id: 123,
  ... # other record columns
  }
]
}

Be sure the sync_id you use is unique. Use something like this in the scan model to generate it on a before_create hook:

  def set_sync_id
    random_token = SecureRandom.urlsafe_base64
    while Scan.where(sync_id: random_token).present? do
      random_token = SecureRandom.urlsafe_base64
    end
    self.sync_id = random_token
  end