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module Gitlab
module SQL
# Class for easily building CTE statements.
#
# Example:
#
# cte = CTE.new(:my_cte_name)
# ns = Arel::Table.new(:namespaces)
#
# cte << Namespace.
# where(ns[:parent_id].eq(some_namespace_id))
#
# Namespace
# with(cte.to_arel).
# from(cte.alias_to(ns))
class CTE
attr_reader :table, :query
# name - The name of the CTE as a String or Symbol.
def initialize(name, query)
@table = Arel::Table.new(name)
@query = query
end
# Returns the Arel relation for this CTE.
def to_arel
sql = Arel::Nodes::SqlLiteral.new("(#{query.to_sql})")
Arel::Nodes::As.new(table, sql)
end
# Returns an "AS" statement that aliases the CTE name as the given table
# name. This allows one to trick ActiveRecord into thinking it's selecting
# from an actual table, when in reality it's selecting from a CTE.
#
# alias_table - The Arel table to use as the alias.
def alias_to(alias_table)
Arel::Nodes::As.new(table, alias_table)
end
# Applies the CTE to the given relation, returning a new one that will
# query from it.
def apply_to(relation)
relation.except(:where)
.with(to_arel)
.from(alias_to(relation.model.arel_table))
end
end
end
end
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