Factory Boy Build JSON String from Another Factory

I am trying to use Factory Boy in order to generate test data for my test suite. My data consists of JSON objects with a body field that contains an escaped JSON String (example below). I also included example python dataclasses and Factory Boy factories for this example data.

Note: For this example, I am skipping the setup of fake data using Faker or the built-in fuzzers to simplify the question. In a more realistic use case, fields like eventtime, deviceid, enqueuedTime would contain rondomized values (using a fixed seed for the randomness)

I am struggling to figure out how to generate the inner JSON object and stringify it using Factory Boy.

An example data point:

{
    "body": "{\"eventdata\":{\"count\":\"1\",\"sourceid\":\"0\",\"updatetime\":\"1579797993879\",\"description\":\"Lorem ipsum dolor sit amet, consectetur adipiscing elit\"},\"eventtime\":\"2020-01-23T16:46:35.522Z\",\"eventversion\":\"1.0.0\",\"eventtype\":\"FooEventType\",\"deviceid\":\"000000123ABC\"}",
    "partition": "30",
    "enqueuedTime": "2020-01-23T16:46:35.594Z",
    "event_type": "FooEventType",
    "year": 2020,
    "month": 1,
    "day": 23}

My Python dataclasses and Factory Boy factories:

from dataclasses import dataclass
import factory

@dataclass
class Root:
  body: str
  partition: str
  enqueued_time: str
  event_type: str
  year: int
  month: int
  day: int

@dataclass
class Eventdata:
  count: str
  sourceid: str
  updatetime: str
  description: str

@dataclass
class Body:
  eventdata: Eventdata
  eventtime: str
  eventversion: str
  eventtype: str
  deviceid: str

class EventdataFactory(factory.Factory):
  class Meta:
    model = Eventdata
  count = "1"
  sourceid = "0"
  updatetime = "1579797993879"
  description = "Lorem ipsum dolor sit amet, consectetur adipiscing elit"

class BodyFactory(factory.Factory):
  class Meta:
    model = Body
  eventdata = factory.SubFactory(Eventdata)
  eventtime = "2020-01-23T16:46:35.522Z"
  eventversion = "1.0.0"
  eventtype = "FooEventType" # Note: It is the same in Root
  deviceid = "000000123ABC"

class RootFactory(factory.Factory):
  class Meta:
    model = Root
  body = "Escaped JSON String" # Need help here
  partition = "30"
  enqueuedTime = "2020-01-23T16:46:35.594Z"
  event_type = "FooEventType" # Note: It is the same in Body
  year = 2020
  month = 1
  day = 23

How do I create the escaped JSON string build from 'BodyFactory' for the body field in 'RootFactory'?