Ruby on Rails 4: Pluck results to hash - ruby

Question

How can I turn:
Person.all.pluck(:id, :name)
to
[{id: 1, name: 'joe'}, {id: 2, name: 'martin'}]
without having to .map every value (since when I add or remove from the .pluck I have to do he same with the .map)

Answer 1

You can map the result:
Person.all.pluck(:id, :name).map { |id, name| {id: id, name: name}}
As mentioned by #alebian:
This is more efficient than
Person.all.as_json(only: [:id, :name])
Reasons:
pluck only returns the used columns (:id, :name) whereas the other solution returns all columns. Depending on the width of the table (number of columns) this makes quite a difference
The pluck solution does not instantiate Person objects, does not need to assign attributes to the models and so on. Instead it just returns an array with one integer and one string.
as_json again has more overhead than the simple map as it is a generic implementation to convert a model to a hash

Answer 2

You could simply do this
Person.select(:id,:name).as_json
You could try this as well
Person.all.as_json(only: [:id, :name])

Answer 3

I see three options:
1) pluck plus map:
Person.pluck(:id, :name).map { |p| { id: p[0], name: p[1] } }
2) pluck plus map plus zip and a variable to make it DRY-er:
attrs = %w(id name)
Person.pluck(*attrs).map { |p| attrs.zip(p).to_h }
3) or you might not use pluck at all although this is much less performant:
Person.all.map { |p| p.slice(:id, :name) }

Answer 4

If you use postgresql, you can use json_build_object function in pluck method:
https://www.postgresql.org/docs/9.5/functions-json.html
That way, you can let db create hashes.
Person.pluck("json_build_object('id', id, 'name', name)")
#=> [{id: 1, name: 'joe'}, {id: 2, name: 'martin'}]

Answer 5

Could go for a hash after the pluck with the ID being the key and the Name being the value:
Person.all.pluck(:id, :name).to_h
{ 1 => 'joe', 2 => 'martin' }
Not sure if this fits your needs, but presenting as an option.

Answer 6

You can use the aptly-named pluck_to_hash gem for this:
https://github.com/girishso/pluck_to_hash
It will extend AR with pluck_to_hash method that works like this:
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}]
It claims to be several times faster than using AR select and as_json

Answer 7

There is pluck_all gem that do almost the same thing as pluck_to_hash do. And it claims that it's 30% faster. (see the benchmark here).
Usage:
Person.pluck_all(:id, :name)

Answer 8

If you have multiple attributes, you may do this for cleanliness:
Item.pluck(:id, :name, :description, :cost, :images).map do |item|
{
id: item[0],
name: item[1],
description: item[2],
cost: item[3],
images: item[4]
}
end

Answer 9

The easiest way is to use the pluck method combined with the zip method.
attrs_array = %w(id name)
Person.all.pluck(attrs_array).map { |ele| attrs_array.zip(ele).to_h }
You can also create a helper method if you are using this method through out your application.
def pluck_to_hash(object, *attrs)
object.pluck(*attrs).map { |ele| attrs.zip(ele).to_h }
end
Consider modifying by declaring self as the default receiver rather than passing Person.all as the object variable.
Read more about zip.

Answer 10

Here is a method that has worked well for me:
def pluck_to_hash(enumerable, *field_names)
enumerable.pluck(*field_names).map do |field_values|
field_names.zip(field_values).each_with_object({}) do |(key, value), result_hash|
result_hash[key] = value
end
end
end

Answer 11

I know it's an old thread but in case someone is looking for simpler version of this
Hash[Person.all(:id, :name)]
Tested in Rails 5.