Very simple multi-tenancy for Rails (shared database)

tenant_model.rb

module TenantModel

  def self.included(base)
    base.extend ClassMethods
    base.instance_eval do
      acts_as_tenant
    end
  end

  class InvalidTenant < SecurityError; end

  module ClassMethods

    def acts_as_tenant
      default_scope -> { where(tenant_id: Tenant.current.id) }

      belongs_to :tenant

      validates_presence_of :tenant_id

      before_validation(:on => :create) do |obj|
        obj.tenant = Tenant.current
      end

      before_save do |obj|
        obj.tenant = Tenant.current
      end

      before_update do |obj|
        raise TenantModel::InvalidTenant unless obj.tenant == Tenant.current
      end

      before_destroy do |obj|
        raise TenantModel::InvalidTenant unless obj.tenant == Tenant.current
      end
    end

  end

end