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# frozen_string_literal: true
module Gitlab
module SQL
# Class for building SQL set operator statements (UNION, INTERSECT, and
# EXCEPT).
#
# ORDER BYs are dropped from the relations as the final sort order is not
# guaranteed any way.
#
# remove_order: false option can be used in special cases where the
# ORDER BY is necessary for the query.
#
# Example usage:
#
# union = Gitlab::SQL::Union.new([user.personal_projects, user.projects])
# sql = union.to_sql
#
# Project.where("id IN (#{sql})")
class SetOperator
def initialize(relations, remove_duplicates: true, remove_order: true)
verify_select_values!(relations) if Rails.env.test? || Rails.env.development?
@relations = relations
@remove_duplicates = remove_duplicates
@remove_order = remove_order
end
def self.operator_keyword
raise NotImplementedError
end
def to_sql
# Some relations may include placeholders for prepared statements, these
# aren't incremented properly when joining relations together this way.
# By using "unprepared_statements" we remove the usage of placeholders
# (thus fixing this problem), at a slight performance cost.
fragments = ApplicationRecord.connection.unprepared_statement do
relations.filter_map do |rel|
next if rel.is_a?(ActiveRecord::NullRelation)
sql = remove_order ? rel.reorder(nil).to_sql : rel.to_sql
sql.presence
end
end
if fragments.any?
"(" + fragments.join(")\n#{operator_keyword_fragment}\n(") + ")"
else
'NULL'
end
end
# UNION [ALL] | INTERSECT [ALL] | EXCEPT [ALL]
def operator_keyword_fragment
remove_duplicates ? self.class.operator_keyword : "#{self.class.operator_keyword} ALL"
end
private
attr_reader :relations, :remove_duplicates, :remove_order
def verify_select_values!(relations)
all_select_values = relations.map do |relation|
if relation.respond_to?(:select_values)
relation.select_values
else
relation.projections # Handle Arel based subqueries
end
end
unless all_select_values.map(&:size).uniq.one?
relation_select_sizes = all_select_values.map.with_index do |select_values, index|
if select_values.empty?
"Relation ##{index}: *, all columns"
else
"Relation ##{index}: #{select_values.size} select values"
end
end
exception_text = <<~EOF
Relations with uneven select values were passed. The UNION query could break when the underlying table changes (add or remove columns).
#{relation_select_sizes.join("\n")}
EOF
raise(exception_text)
end
end
end
end
end
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