Method: Dynamoid::Criteria::Chain#pluck

Defined in:
lib/dynamoid/criteria/chain.rb

#pluck(*args) ⇒ Array

Select only specified fields.

It takes one or more field names and returns an array of either values or arrays of values.

Post.pluck(:id)                   # => ['1', '2']
Post.pluck(:title, :title)        # => [['1', 'Title #1'], ['2', 'Title#2']]

Post.where('views_count.gt' => 1000).pluck(:title)

There are some differences between pluck and project. pluck

  • doesn’t instantiate models

  • it isn’t chainable and returns Array instead of Chain

It deserializes values if a field type isn’t supported by DynamoDB natively.

It can be used to avoid loading large field values and to decrease a memory footprint.



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# File 'lib/dynamoid/criteria/chain.rb', line 490

def pluck(*args)
  fields = args.map(&:to_sym)

  # `project` has a side effect - it sets `@project` instance variable.
  # So use a duplicate to not pollute original chain.
  scope = dup
  scope.project(*fields)

  if fields.many?
    scope.items.map do |item|
      fields.map { |key| Undumping.undump_field(item[key], source.attributes[key]) }
    end.to_a
  else
    key = fields.first
    scope.items.map { |item| Undumping.undump_field(item[key], source.attributes[key]) }.to_a
  end
end