Return Single Field with Rails Query

Question

I'm having trouble with something that should be so easy, but I don't know what I'm doing wrong. I'm simply trying to do a query that returns a single field instead of the complete record in Rails 3.

model method

def self.find_user_username(user_id)
  user_name = User.select("user_name").where(user_id)
  return user_name
end

I'm staring at the Rails Guide ( http://guides.rubyonrails.org/active_record_querying.html#selecting-specific-fields) and it simply says (where viewable_by, locked = fields):

Client.select("viewable_by, locked")

I've tried flip flopping the select, like so:

User.select("user_name").where(user_id) - AND - 
User.where(user_id).select("user_name")

but neither work. In fact, I even tried:

user_name = User.select("yoda").where(user_id)

and I didn't get an error. When I look in the view, where I have:

Friend.find_user_username(friend.user_id)

I just keep getting the hash: ActiveRecord::Relation:0x2f4942f0

Answer 1

User.where(:id => user_id).pluck(:user_name).first

Should do what you're trying to do.

pluck "accepts a column name as argument and returns an array of values of the specified column with the corresponding data type"

Answer 2

Rails 6 introduced ActiveRecord::Relation#pick.

pick(:foo) is equivalent to limit(1).pluck(:foo).first.