Ecto builder Arithmetic support

builder.ex

  # The idea is to add support for something like.
  # query = from s in Subscription,
  #         order_by: s.price + s.registration_fee
  #
  # subscriptions = Repo.all(query)
  
  # Arithmetic
  def escape({operator, _, [left, right]} = expr, type, params, vars, env) when operator in ~w(+ - * /)a  do
    ltype = quoted_type(right, vars)
    rtype = quoted_type(left, vars)

    {left,  params} = escape(left, ltype, params, vars, env)
    {right, params} = escape(right, rtype, params, vars, env)

    {{:{}, [], [operator, [], [left, right]]}, params}
  end
  
  # But this yields the following query, notice the ORDER BY, at the end.
  # [debug] SELECT s0."id", s0."name", s0."price", s0."registration_fee", s0."call_time", s0."binding_period", s0."has_4g", s0."free_sms", s0."intro_discount", s0."endpoint", s0."data", s0."company_id", s0."inserted_at", s0."updated_at" FROM "subscriptions" AS s0 ORDER BY +(s0."call_time", s0."call_time") [] ERROR query=0.2ms