You have a multitenant system, where each tenant is only aware of the instances of a model which belong to them. Let's say our tenants are organizations, and each organization has many customers.
1 2 3 4 class CustomersController < ApplicationController load_and_authorize_resource :organization load_and_authorize_resource :customer, :through => :organization end
Now assume we have two organizations: Foo and Bar.
Foo comes along and creates two customers, which are assigned IDs
2; next Bar creates a customer, which gets ID
3; then Foo creates a third customer, which gets ID
There are a few undesirable properties with this system:
- From an organization's perspective, the IDs are non-contiguous, so Foo sees customers
4, with no explanation where 3 went.
- Any organization will be able to infer the total number of customers across all organizations.
The underlying issue with both of these properties is that it makes an organization aware of the existence of other organizations.
We had a few goals for our solution:
- Keep our existing surrogate keys i.e. the
- Be general enough to apply not only to
Customer, but to any per-organization model added in the future.
Based on this we used a solution in three parts:
We will use an
organization_object_counterstable to keep track of how many instances of each model an organization has. This table will offer functionality similar to counter cache, but it will not decrement when an instance of a model is deleted (since we do not wish to reuse IDs).
Any model which is scoped to an organization such as
Customerwill gain an
id_within_organizationcolumn. More generally we'll say that if a model
belongs_to :organization, then it should have an
When a new instance of such a model is persisted, we will set its
id_within_organizationto the current
organization_object_countersfor that organization and model. Once that is done we will increment the count ready for the next object.
Firstly we add the table to track our
next_id for each pairing of organization and model. Note we also add an index, which serves the dual purpose of improving performance and ensuring we only have one
next_id for each pairing on organization and model.
1 2 3 4 5 6 7 8 9 10 def change create_table :organization_object_counters do |t| t.references :organization, null: false t.string :klass, null: false t.integer :next_id, null: false, default: 1 end add_index :organization_object_counters, [:organization_id, :klass], unique: true, name: 'index_organization_object_counters' end
Next we identify any model which
belongs_to :organization and give it an
id_within_organization. Since we'll always be looking this up along with an
organization_id, we add a composite index including both.
1 2 3 4 5 6 7 8 class AddIdWithOrganizationToCustomers < ActiveRecord::Migration def change add_column :customers, :id_within_organization, :integer, null: false add_index :customers, [:organization_id, :id_within_organization], unique: true, name: 'index_customers_on_id_within_organization' end end
We will define an
ActiveSupport:Concern to encapsulate the
id_within_organization behavior described above. If
create fails for any reason, the
counter.increment! will rollback because the
yield will take place within a transaction.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 module IdentifierWithinOrganization extend ActiveSupport::Concern included do around_create :set_id_within_organization private def set_id_within_organization counter = organization.object_counters.whereklass: self.class.base_class.name.first_or_create self.id_within_organization = counter.next_id yield counter.increment! :next_id end end end
Finally we can
include IdentifierWithinOrganization in our
id_within_organization for each instance of a model is useful on its own, but if you're already using cancancan's
load_and_authorize_resource method then switching to use it your paths is as easy as:
- Have links use
id_within_organizationas their param, by adding a default
to_paramimplementation in the
id_within_organizationto load resources by specify a
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