sql,ruby-on-rails,ruby,ruby-on-rails-4,activerecord , rails has_many at least one children has the value


rails has_many at least one children has the value

Question:

Tag: sql,ruby-on-rails,ruby,ruby-on-rails-4,activerecord

Let say I have a Group of Users and User has a enum, which described it's mood.

class Group < AR::Base
  has_many :users

class User < AR::Base
  belongs_to :group
  enum mood: %i(good bad ugly)

How can I find all groups, where at least one User has the good mood?

Which index should I add for optimizing this query?


Answer:

You can use joins method.

Group.joins(:users).where("users.mood = ?", User.moods[:good])

You can add this into your migration

add_index :users, :group_id

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