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module Arel
module SqlCompiler
class PostgreSQLCompiler < GenericCompiler
def select_sql
if !relation.orders.blank? && using_distinct_on?
subquery = build_query \
"SELECT #{select_clauses.kind_of?(::Array) ? select_clauses.join("") : select_clauses.to_s}",
"FROM #{from_clauses}",
(joins(self) unless joins(self).blank? ),
("WHERE #{where_clauses.join(" AND ")}" unless wheres.blank? ),
("GROUP BY #{group_clauses.join(', ')}" unless groupings.blank? ),
("HAVING #{having_clauses.join(', ')}" unless havings.blank? ),
("#{locked}" unless locked.blank? )
build_query \
"SELECT * FROM (#{subquery}) AS id_list",
"ORDER BY #{aliased_orders(order_clauses)}",
("LIMIT #{taken}" unless taken.blank? ),
("OFFSET #{skipped}" unless skipped.blank? )
else
super
end
end
def using_distinct_on?
relation.select_clauses.any? { |x| x =~ /DISTINCT ON/ }
end
def aliased_orders(orders)
# PostgreSQL does not allow arbitrary ordering when using DISTINCT ON, so we work around this
# by wrapping the +sql+ string as a sub-select and ordering in that query.
order = orders.join(', ').split(/,/).map { |s| s.strip }.reject(&:blank?)
order = order.zip((0...order.size).to_a).map { |s,i| "id_list.alias_#{i} #{'DESC' if s =~ /\bdesc$/i}" }.join(', ')
end
def supports_insert_with_returning?
engine.connection.send(:postgresql_version) >= 80200
end
end
end
end
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