Rails 4 makes this too easy 🙂 Foo.where.not(id: Bar.select(:foo_id).uniq) this outputs the same query as jdoe’s answer SELECT “foos”.* FROM “foos” WHERE “foos”.”id” NOT IN ( SELECT DISTINCT “bars”.”foo_id” FROM “bars” ) And as a scope: scope :lonely, -> { where.not(id: Bar.select(:item_id).uniq) }
The way is to define additional extending selector to has_many scope: class Customer < ActiveRecord::Base has_many :orders do def by_account(account) # use `self` here to access to current `Customer` record where(:account_id => account.id) end end end customers.orders.by_account(account) The approach is described in Association Extension head in Rails Association page. To access the Customer record in … Read more
Or are scopes not the same as roles? The biggest difference between the two is the context they apply to. Role-based Access Control (RBAC) governs the access control of a user when using the web application directly, while Oauth-2 scope governs the access to the API resources for an external client on behalf of a … Read more
There was more of a difference in Rails 2.x, since named_scopes did not execute your queries (so you could chain them), whereas class methods generally did execute the queries (so you could not chain them), unless you manually wrapped your query in a scoped(…) call. In Rails 3, everything returns an ActiveRecord::Relation until you need … Read more