Ensure only one record has specific value for another associated record | Rails 6.1.4

I couldn't come up with a better title, but for my app for landlords I faced a problem where I don't want to remove old tenants. I want to store them in a database for future reference. So that leaves me with problem of making sure that only one tenant can have "active" status at any given time.

Now, I tried to find a way of forcing that on a database level, but then I thought about rails validations. I can check that on adding or modifying my tenants. And since my app will never be big enough for multiple users to update the same record in DB concurrently, I decided to implement that directly in the app.

---

Let's assume our Flat has_many :tenants and Tenant belongs_to :flat

I will take advantage of rails model callback order. And first four go as below:

1. before_validation
2. after_validation
3. before_save
4. around_save

So now I can use this order to force validation of my record to see if any other tenants are active. If there is another tenant that is active, I won't allow the record to save. Sounds simple to me.

	validate :force_one_active
	def force_one_active
	flat = Flat.find_by(id: flat_id)
	determine_active
	if self.active?
	other_tenants = Tenant.where(flat_id: flat_id, active: true).where("rent_to >= ? ", Date.today)
	end
	if other_tenants.present? && flat.taken_until > Date.today
	errors.add(:flat_id, I18n.t('forms.too_many_active'))
	end
	end
	def determine_active
	if rent_from <= Date.today && rent_to >= Date.today
	self.active = true
	else
	self.active = false
	end
	end

view raw tenant.rb hosted with ❤ by GitHub

Few things happened above. I use my method determine_active in my validation. I do that because in my force_one_active function, it first checks if the tenant should be active at all, then performs a search to check if there are any additional tenants with the same status, if it happens to find that the flat is occupied, it stops the record from saving on a validation level, thus leaving active = false.

I've also added another function to set flat's taken value if our current tenant happened to be active.

	before_save :occupy_flat
	def occupy_flat
	flat = Flat.find_by(id: flat_id)
	if self.active?
	flat.taken = true
	flat.taken_until = self.rent_to
	flat.save!
	else
	flat.taken = false
	flat.taken_until = self.rent_to
	flat.save!
	end
	end

view raw tenant.rb hosted with ❤ by GitHub

Now, because this method is in before_save callback it will never run unless validation has passed successfully, as per order shown previously.

It's not perfect, but it works for a smaller scale app like mine.