How do I write a UNION chain with ActiveRelation?

Question

I need to be able to chain an arbitrary number of sub-selects with UNION using ActiveRelation.

I\'m a little confused by the ARel implementation of this, si

Answer 1

I like Squeel. But don't use it. So I came to this solution (Arel 4.0.2)

def build_union(left, right)
  if right.length > 1
    Arel::Nodes::UnionAll.new(left, build_union(right[0], right[1..-1]))
  else
    Arel::Nodes::UnionAll.new(left, right[0])
  end
end

managers = [select_manager_1, select_manager_2, select_manager_3]
build_union(managers[0], managers[1..-1]).to_sql
# => ( (SELECT table1.* from table1)
#    UNION ALL
#    ( (SELECT table2.* from table2)
#    UNION ALL
#    (SELECT table3.* from table3) ) )