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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