How to serialize a Marshmallow field under a different name

Question

I want a Marshmallow Schema with the following output json -

{
  "_id": "aae216334c3611e78a3e06148752fd79",
  "_time": 20.79606056213379,
  "more_data" : {...}
}

Marshmallow doesn't serialize private members so this is as close as I can get -

class ApiSchema(Schema):
    class Meta:
        strict = True

    time = fields.Number()
    id = fields.String()

But I do need the underscores in the output json.

Is there a way to tell Marshmallow to serialize the fields using different names?

Answer 1

The accepted answer (using attribute) didn't work for me, possibly because:

Note: This should only be used for very specific use cases such as outputting multiple fields for a single attribute. In most cases, you should use data_key instead.

However data_key worked nicely:

class ApiSchema(Schema):
    class Meta:
        strict = True

    _time = fields.Number(data_key="time")
    _id = fields.String(data_key="id")

Answer 2

https://marshmallow.readthedocs.io/en/2.x-line/quickstart.html#specifying-attribute-names

Even though the docs are for version 2, this seems to still work as of 3.5.1. The stable version 3 docs will not have this example.

class ApiSchema(Schema):
  class Meta:
      strict = True

  _time = fields.Number(attribute="time")
  _id = fields.String(attribute="id")

Answer 3

The answer's well documented in Marshmallows api reference.

I need to use dump_to :

class ApiSchema(Schema):
    class Meta:
        strict = True

    time = fields.Number(dump_to='_time')
    id = fields.String(dump_to='_id')