How to resolve pydantic model is not JSON serializable

Question

I am having below pydantic models.

class SubModel(BaseModel):
    columns: Mapping
    key: List[str]
    required: Optional[List[str]]

    class Config:
        anystr_strip_whitespace: True
        extra: Extra.allow
        allow_population_by_field_name: True


class MyModel(BaseModel):
    name: str
    config1: Optional[SubModel]
    config2: Optional[Mapping]
    class Config:
        anystr_strip_whitespace: True
        extra: Extra.allow
        allow_population_by_field_name: True

When I am trying to do a dumps on this, I am getting model is not JSON serializable

from io import BytesIO
from orjson import dumps
    
bucket = s3.Bucket(bucket_name)
bucket.upload(BytesIO(dumps(data)), key, ExtraArgs={'ContentType': 'application/json'})

Error -

TypeError: Type is not JSON serializable: MyModel

data is a normal python dictionary with one of item of type MyModel. Tried to use .json() but get dict has no attribute json.

I am stuck here. Can someone help me.

Have you resolved this issue? – eirenikos Aug 07 '21 at 15:34 — eirenikos, Aug 07 '21 at 15:34

score 11 · Answer 1 · edited Oct 18 '21 at 15:36

11

Got similar isse for FastAPI response, solved by:

return JSONResponse(content=jsonable_encoder(item), status_code=200)

or can be just like this:

return jsonable_encoder(item)

where jsonable_encoder is:

from fastapi.encoders import jsonable_encoder

More details are here: https://fastapi.tiangolo.com/tutorial/encoder/

edited Oct 18 '21 at 15:36

Dharman

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answered Oct 18 '21 at 15:31

Taraskin

561
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score 2 · Answer 2 · answered Jul 18 '22 at 19:37

What about just setting a default encoder (which is used if all else fails)?

orjson.dumps(
    MyModel(name="asd"),
    default=lambda x: x.dict()
)
# Output: b'{"name":"asd","config1":null,"config2":null}'

Or with more nested:

orjson.dumps(
    {"a_key": MyModel(name="asd")}, 
    default=lambda x: x.dict()
)
# Output: b'{"a_key":{"name":"asd","config1":null,"config2":null}}'

If you have other types than Pydantic, just make a function and handle all types you have separately.

It also works with json library from standard library (for those that don't use orjson).

score 1 · Answer 3 · answered May 21 '22 at 10:43

Here the problem is that pydantic models are not json serializable by default, in your case, you can call data.dict() to serialize a dict version of your model.

from io import BytesIO
from orjson import dumps

bucket = s3.Bucket(bucket_name)
bucket.upload(BytesIO(dumps(data.dict())), key, ExtraArgs={'ContentType': 'application/json'})

How to resolve pydantic model is not JSON serializable

3 Answers3