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": "[email protected]",
"created_at": "2013-10-17T02:29:15.638Z",
"updated_at": "2013-10-17T02:29:15.638Z",
"password_digest": "$2a$10$taHk3udtWN61Il5I18akj.E90AB1TmdL1BkQBKPk/4eZ7YyizGOli",
"remember_token": "118f807d0773873fb5e4cd3b5d98048aef4f6f59",
"admin": false

...
}

But I would like to omit certain certain fields from this API, so I use pluck

def jsontest
  @users = User.all.limit(10).pluck(:id, :name, :email, :created_at) ###
  render json: @users
end

but pluck returns an array of only values, when I would like to have each object's attributes accessible by hash key.

[
...

    7,
    "Sage Smith",
    "[email protected]",
    "2013-10-17T02:29:15.638Z"

...    

]

So how can I effectively pluck the values and their keys?

I realize I could sweep through @users and grab the keys before plucking and recreate the hash, but I'm expecting there to be some convenience method that does exactly what I want.

Answer 1

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(*%i[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 2

Use select instead of pluck:

def jsontest
  @users = User.select('id, name, email, created_at').limit(10)
  render json: @users
end

Answer 3

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}]
#