Class: RuboCop::Cop::Rails::Pluck

Inherits:
Base
  • Object
show all
Extended by:
AutoCorrector, TargetRailsVersion
Defined in:
lib/rubocop/cop/rails/pluck.rb

Overview

Enforces the use of ‘pluck` over `map`.

‘pluck` can be used instead of `map` to extract a single key from each element in an enumerable. When called on an Active Record relation, it results in a more efficient query that only selects the necessary key.

NOTE: If the receiver’s relation is not loaded and ‘pluck` is used inside an iteration, it may result in N+1 queries because `pluck` queries the database on each iteration. This cop ignores offenses for `map/collect` when they are suspected to be part of an iteration to prevent such potential issues.

source,ruby

users = User.all 5.times do

users.map { |user| user[:foo] } # Only one query is executed

end

users = User.all 5.times do

users.pluck(:id) # A query is executed on every iteration

end

If a method call has no receiver, like ‘do_something { users.map { |user| user }`, it is not considered part of an iteration and will be detected.

Examples:

# bad
Post.published.map { |post| post[:title] }
[{ a: :b, c: :d }].collect { |el| el[:a] }

# good
Post.published.pluck(:title)
[{ a: :b, c: :d }].pluck(:a)

Constant Summary collapse

MSG = 
'Prefer `%<replacement>s` over `%<current>s`.'

Constants included from TargetRailsVersion

TargetRailsVersion::TARGET_GEM_NAME, TargetRailsVersion::USES_REQUIRES_GEM_API

Instance Method Summary collapse

Methods included from TargetRailsVersion

minimum_target_rails_version, support_target_rails_version?

Instance Method Details

#on_block(node) ⇒ Object Also known as: on_numblock, on_itblock

rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity



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# File 'lib/rubocop/cop/rails/pluck.rb', line 66

def on_block(node)
  return if node.each_ancestor(:any_block).first&.receiver

  pluck_candidate?(node) do |argument, key|
    next if key.regexp_type? || !use_one_block_argument?(argument)

    match = if node.block_type?
              block_argument = argument.children.first.source
              use_block_argument_in_key?(block_argument, key)
            elsif node.numblock_type?
              use_block_argument_in_key?('_1', key)
            else # itblock
              use_block_argument_in_key?('it', key)
            end
    next unless match

    register_offense(node, key)
  end
end