How can I have ActiveRecord's pluck also return the column name for rendering in json?

Question

def jsontest
   @users = User.all.limit(10)
   render json: @users
end

yields

{
...

\"id\": 7,
\"name\": \"Sage Smith\",
\"email\"         


        

Answer 1

You can pull the data along with the column name as:

@users = User.all.limit(10)
                 .pluck(:id, :name, :email, :created_at)
                 .map {|id, name, email, created_at| { id: id, name: name, 
                                                       email: email, 
                                                       created_at: created_at } }

This will pull the data and map it according to how you want it. One advantage of using pluck over select is that you can use joins along with it.

Answer 2

@girishso's gem is great, but my project is in Rails 3. It doesn't work.

This article is helpful to me, or install pluck_all gem to achieve this.

Usage:

User.limit(10).pluck_all(:id, :name, :email, :created_at)

Answer 3

Fastest way to return hash of users with selected columns is use ActiveRecord::Base.connection.select_all method.

sql = User.select('id, name, email, created_at').limit(10).to_sql
@users = ActiveRecord::Base.connection.select_all(sql)
render json: @users

Answer 4

@andrewCone - It should be like this:

User.limit(:10).pluck_to_hash([:id, :name, :email, :created_at])

Answer 5

vee's answer is good, but I have one caveat. select instantiates a User for every row in the result, but pluck does not. That doesn't matter if you are only returning a few objects, but if you are returning large batches (50, 100, etc) you'll pay a significant performance penalty.

I ran into this problem, and I switched back to pluck:

#in user.rb
def self.pluck_to_hash(keys)
  pluck(*keys).map{|pa| Hash[keys.zip(pa)]}
end

#in elsewhere.rb
User.limit(:10).pluck_to_hash(['id, name, email, created_at'])

It's ugly, but it gets the hash you want, and fast.

I've updated it to reflect Mike Campbell's comment on Oct 11.

Answer 6

Created a simple pluck_to_hash gem to achieve this. https://github.com/girishso/pluck_to_hash

Usage example..

Post.limit(2).pluck_to_hash([:id, :title])
#
# [{:id=>213, :title=>"foo"}, {:id=>214, :title=>"bar"}]
#

Post.limit(2).pluck_to_hash(:id)
#
# [{:id=>213}, {:id=>214}]
#

# Or use the shorter alias pluck_h

Post.limit(2).pluck_h(:id)
#
# [{:id=>213}, {:id=>214}]
#