查找具有特定关联的用户的最佳方法

Question

Lets say I have a User model and each user has an association called user_logins which is created every time they login, storing information about their login.

What I need to do is find all users that have 5 user_login records, where the fifth record was created today.

Something like this:

users = User.all.where(user_logins_count == 5, user_login.last.created_at == today)

user_logins_count is a counter cache I have set up.

Of course that code is brutal, but hopefully it'll elaborate on what I'm trying to achieve.

PG ERROR

rake aborted!
ActiveRecord::StatementInvalid: PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "last
"
LINE 1: ...n_logins_count" = 5 GROUP BY humans.id HAVING MAX(human_logi...
                                                             ^

New code:

humans = user.humans.joins(:human_logins).where(human_logins_count: 5)
        .group('humans.id')
        .having('MAX(human_logins.created_at) >= ?', Date.today)

Answer 1

You can define this as a scope inside the User class:

class User
  scope :logged_in_a_lot_today, -> do
    joins(:user_logins).where(user_logins_count: 5)
      .group('users.id')
      .having('MAX(user_logins.created_at) >= ?', Date.today)
  end
end

Now you can simply get these users with:

User.logged_in_a_lot_today

Since it's defined as a scope, you can also add more conditions if you'd like to:

User.logged_in_a_lot_today.where(name: 'John Doe')

Note that it would probably be a good idea to set up a partial index (if your database supports it) on users who have a user_logins_count of 5.