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# frozen_string_literal: true
module RuboCop
module Cop
module UsageData
# Allows counts only for selected tables' foreign keys for `distinct_count` method.
#
# Because distinct_counts over large tables' foreign keys will take a long time
#
# @example
#
# # bad because pipeline_id points to a large table
# distinct_count(Ci::Build, :commit_id)
#
class DistinctCountByLargeForeignKey < RuboCop::Cop::Cop
MSG = 'Avoid doing `%s` on foreign keys for large tables having above 100 million rows.'.freeze
def_node_matcher :distinct_count?, <<-PATTERN
(send _ $:distinct_count $...)
PATTERN
def on_send(node)
distinct_count?(node) do |method_name, method_arguments|
next unless method_arguments && method_arguments.length >= 2
next if allowed_foreign_key?(method_arguments[1])
add_offense(node, location: :selector, message: format(MSG, method_name))
end
end
private
def allowed_foreign_key?(key)
key.type == :sym && allowed_foreign_keys.include?(key.value)
end
def allowed_foreign_keys
cop_config['AllowedForeignKeys'] || []
end
end
end
end
end
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