ecto_dynamic_query.ex

defmodule Bmgr.Transaction.SearchQuery do
  import Ecto.Query

  alias Bmgr.{Transaction}

  @filters [:account, :status]

  def build(filter_params) do
    do_filter(Transaction, @filters, filter_params)
  end

  defp do_filter(query, filters, params) when is_list(filters) do
    Enum.reduce(filters, query, fn (filter, acc) ->
      do_filter(acc, filter, params)
    end)
  end
  defp do_filter(query, :account, %{"account" => value}) do
    from(t in query, preload: [entries: from(e in Entry, where: e.account_id == ^value)])
  end
 
  defp do_filter(query, :status, %{"status" => value}) do
    from(t in query, where: t.status == ^value)
  end

  defp do_filter(query, _, _) do
    query
  end
end