Returns primary key consraints.

  :pkname: if a string, returns a dict with pkname=pkey. pkname and pkey must be enumerables of
  matching length.

def get_id_constraints(pkname, pkey):
  """Returns primary key consraints.

  :pkname: if a string, returns a dict with pkname=pkey. pkname and pkey must be enumerables of
  matching length.
  """
  if isinstance(pkname, str):
    return {pkname: pkey}
  else:
    return dict(zip(pkname, pkey))