where for querying an array attribute in rails model - ruby

Question

I have a user model with an array of roles.
u=User.first
u.roles = ['admin']
v=User.last
u.roles = ['admin', 'member']
How do i query to fetch all users with admin role?
Edit:
roles is a serialized array for the user model
User Model:
serialize :roles
Migration:
add_column :users, :roles, :string, default: []

Answer 1

Depends on what "roles" means:
If it is an association as in
class User < ActiveRecord::Base
has_many :roles
end
Then you look up the role and fetch all users:
Role.find_by_name("admin").users
or roles is just a column and it is serialised, in which case you can instantiate all users (slow)
User.all.select { |u| u.roles.include? "admin" }
Or query the database directly which is more complex and depends on the adapter.
My opinion: I would avoid using serialised columns, when relations can do. They are cumbersome in every way: Forms, Searches, Selects...

Answer 2

Another way is using scopes:
Model user.rb:
class User
scope :admins, -> () { where("roles #> ?", '{admin}')}
scope :by_roles, -> (roles) { where("roles #> ?", "{#{roles.join(', ')}}") }
end
Scoped calls, with results
Admins:
3.0.0 :001 > User.admins
User Load (0.4ms) SELECT "users".* FROM "users" WHERE (roles #> '{admin}') /* loading for inspect */ LIMIT $1 [["LIMIT", 11]]
=> #<ActiveRecord::Relation [#<User id: 1, account_uuid: "0812df2d-58ed-4231-aca5-ec7708a156bb", email: "admin#example.com", password_digest: [FILTERED], first_name: "Admin", last_name: "Admin" remember_token: nil, remember_token_expires_at: nil, roles: ["user", "admin"], created_at: "2021-12-02 11:51:50.684788000 +0000", updated_at: "2021-12-02 11:51:50.684788000 +0000">]>
Users by_roles within single role:
3.0.0 :002 > User.by_roles(['user'])
User Load (0.5ms) SELECT "users".* FROM "users" WHERE (roles #> '{user}') /* loading for inspect */ LIMIT $1 [["LIMIT", 11]]
=> #<ActiveRecord::Relation [#<User id: 1, account_uuid: "0812df2d-58ed-4231-aca5-ec7708a156bb", email: "admin#example.com", password_digest: [FILTERED], first_name: "Admin", last_name: "Admin", remember_token: nil, remember_token_expires_at: nil, roles: ["user", "admin"], created_at: "2021-12-02 11:51:50.684788000 +0000", updated_at: "2021-12-02 11:51:50.684788000 +0000">, #<User id: 2, account_uuid: "7a09830d-bfde-45eb-abeb-4b305a7bb374", email: "user_1#example.com", password_digest: [FILTERED], first_name: "User", last_name: "Adviseman", remember_token: nil, remember_token_expires_at: nil, roles: ["user"], created_at: "2021-12-02 17:40:12.172547000 +0000", updated_at: "2021-12-02 17:40:12.172547000 +0000">, #<User id: 3, account_uuid: "a0044954-6ad0-4d8f-9681-bd5dfcfa72b7", email: "user_2#example.com", password_digest: [FILTERED], first_name: "User", last_name: "Adviseman", remember_token: nil, remember_token_expires_at: nil, roles: ["user"], created_at: "2021-12-02 17:40:12.583594000 +0000", updated_at: "2021-12-02 17:40:12.583594000 +0000">, #<User id: 4, account_uuid: "7d26e5d5-beaf-48bd-ad98-f53044a7182b", email: "user_3#example.com", password_digest: [FILTERED], first_name: "User", last_name: "Adviseman", remember_token: nil, remember_token_expires_at: nil, roles: ["user"], created_at: "2021-12-02 17:40:12.847412000 +0000", updated_at: "2021-12-02 17:40:12.847412000 +0000">]>
Users by_roles within multiple roles:
3.0.0 :003 > User.by_roles(['user', 'admin'])
User Load (0.6ms) SELECT "users".* FROM "users" WHERE (roles #> '{user, admin}') /* loading for inspect */ LIMIT $1 [["LIMIT", 11]]
=> #<ActiveRecord::Relation [#<User id: 1, account_uuid: "0812df2d-58ed-4231-aca5-ec7708a156bb", email: "admin#example.com", password_digest: [FILTERED], first_name: "Admin", last_name: "Bezugliy", remember_token: nil, remember_token_expires_at: nil, roles: ["user", "admin"], created_at: "2021-12-02 11:51:50.684788000 +0000", updated_at: "2021-12-02 11:51:50.684788000 +0000">]>