code: def separate_fields(fields):
      
      flat_fields = {}
      nested_fields = {}
  
      # exclude "id" and "meta" elements
      for k, v in fields.items():
          # TODO: remove dependence on KEYS_TO_INCLUDE
          if k not in KEYS_TO_EXCLUDE:
              if type(v) not in [type({}), type([])]:
                  flat_fields.update({k: v})
              else:
                  nested_fields.update({k: v})
  
      return flat_fields, nested_fields
docs: Non-foreign key fields can be mapped to new article instances
      directly. Foreign key fields require a bit more work.
      This method returns a tuple, of the same format:
      (flat fields, nested fields)