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module Arel
module Visitors
class PostgreSQL < Arel::Visitors::ToSql
private
def visit_Arel_Nodes_SelectStatement o
if !o.orders.empty? && using_distinct_on?(o)
subquery = o.dup
subquery.orders = []
subquery.limit = nil
subquery.offset = nil
sql = super(subquery)
[
"SELECT * FROM (#{sql}) AS id_list",
"ORDER BY #{aliased_orders(o.orders).join(', ')}",
("LIMIT #{o.limit}" if o.limit),
(visit(o.offset) if o.offset),
].compact.join ' '
else
super
end
end
def using_distinct_on?(o)
o.cores.any? do |core|
core.projections.any? do |projection|
/DISTINCT ON/ === projection
end
end
end
def aliased_orders orders
#orders = o.orders.map { |x| visit x }.join(', ').split(',')
list = []
orders.each_with_index do |o,i|
list <<
[
"id_list.alias_#{i}",
(o.index(/desc/i) && 'DESC')
].compact.join(' ')
end
list
end
end
end
end
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