dynamic_where.ex

@doc """
You can pipe queries into this build_where/3
fn and match on operators like :in, :==,
:ilike, etc and handle the particular
where semantics in each function case.
Pay attention to the positional binding 
[...,e] which will capture the last 
binding added to the piped in query.
See also: https://hexdocs.pm/ecto/Ecto.Query.html#module-positional-bindings
and.      https://hexdocs.pm/ecto/Ecto.Query.API.html#field/2
"""
def build_where(query, :in, from_api) do
  query
  |> where([..., e], 
    field(e, ^from_api.field) 
    in ^from_api.values)
end