pydantic convert to jsonable dict (not full json string)

Question

I’d like to use pydantic for handling data (bidirectionally) between an api and datastore due to it’s nice support for several types I care about that are not natively json-serializable. It has better read/validation support than the current approach, but I also need to create json-serializable dict objects to write out.

from uuid import UUID, uuid4
from pydantic import BaseModel

class Model(BaseModel):
    the_id: UUID

instance = Model(the_id=uuid4())
print("1: %s" % instance.dict()
print("2: %s" % instance.json()

prints

{'the_id': UUID('4108356a-556e-484b-9447-07b56a664763')}
>>> inst.json()
'{"the_id": "4108356a-556e-484b-9447-07b56a664763"}'

Id like the following:

{"the_id": "4108356a-556e-484b-9447-07b56a664763"} # eg "json-compatible" dict

It appears that while pydantic has all the mappings, but I can’t find any usage of the serialization outside the standard json ~recursive encoder (json.dumps( ... default=pydantic_encoder)) in pydantic/main.py. but I’d prefer to keep to one library for both validate raw->obj (pydantic is great at this) as well as the obj->raw(dict) so that I don’t have to manage multiple serialization mappings. I suppose I could implement something similar to the json usage of the encoder, but this should be a common use case?

Other approaches such as dataclasses(builtin) + libraries such as dataclasses_jsonschema provide this ~serialization to json-ready dict, but again, hoping to use pydantic for the more robust input validation while keeping things symmetrical.

Asked By: some bits flipped

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Source

Answer 1

The current version of pydantic does not support creating jsonable dict straightforwardly. But you can use the following trick:

class Model(BaseModel):
    the_id: UUID = Field(default_factory=uuid4)

print(json.loads(Model().json()))

{'the_id': '4c94e7bc-78fe-48ea-8c3b-83c180437774'}

Or more efficiently by means of orjson

orjson.loads(Model().json())

Answered By: alex_noname

Answer 2

it appears this functionality has been proposed, and (may be) favored by pydantic’s author samuel colvin, as https://github.com/samuelcolvin/pydantic/issues/951#issuecomment-552463606

which proposes adding a simplify parameter to Model.dict() to output jsonalbe data.

This code runs in a production api layer, and is exersized such that we can’t use the one-line workaround suggested (just doing a full serialize (.json()) + full deserialize). We implemented a custom function to do this, descending the result of .dict() and converting types to jsonable – hopefully the above proposed functionality is added to pydantic in the future.

Answered By: some bits flipped

Answer 3

Another alternative is to use the jsonable_encoder method from fastapi if you’re using that already: https://fastapi.tiangolo.com/tutorial/encoder/

The code seems pretty self-contained so you could copy paste it if the license allows it.

Answered By: aiguofer

Answer 4

The official method in Pydantic 2 (which is not released as of this answer) is using the .model_dump() method with mode="json" argument:

print(instance.model_dump(mode="json"))

From the Pydantic 2 Plan document:

def model_dump_json(self, ...) -> str:
   """
   previously `json()`, arguments as above
   effectively equivalent to `json.dump(self.model_dump(..., mode='json'))`,
   but more performant
   """

Answered By: Selcuk

pydantic convert to jsonable dict (not full json string)

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