Create an endpoint that accepts a single item or an array of items.

[aodj-kara]

I'm currently migrating a project to flask-openapi3, and I'm trying to work out how to correctly setup the body to accept either a single item or an array or items

class Body(BaseModel):
    user_id: int
    message: str

@app.post("/message")
def send_message(body: Body):
    ...

If I configure it as the above, I can accept a single payload, but if I change the body definition to this, I get an exception

@app.post("/message")
def send_message(body: Body | list[Body]):
    ...

AssertionError: Body | list[Body] is invalid `pydantic.BaseModel`

Can anyone advise how I might be able to accomplish this?

[aodj-kara]

I also tried using the RootModel which doesn't work

from pydantic import BaseModel, RootModel

class Body(BaseModel):
    user_id: int
    message: str

OneOrManyMessages = RootModel[Body | list[Body]]

@app.post("/message")
def send_message(body: OneOrManyMessages):
    ...

  ...
  File "api/.venv/lib/python3.11/site-packages/flask_openapi3/utils.py", line 292, in parse_body
    schema = get_model_schema(body)
             ^^^^^^^^^^^^^^^^^^^^^^
  File "api/.venv/lib/python3.11/site-packages/flask_openapi3/utils.py", line 123, in get_model_schema
    assert inspect.isclass(model) and issubclass(model, BaseModel), \
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: root=Body | list[Body] is invalid `pydantic.BaseModel`

Digging into it a little more, I can't quite see what the issue is; my guess is the validation being done can't handle it

In [1]: from flask_openapi3.utils import get_model_schema

In [2]: from pydantic import BaseModel, RootModel
   ...: 
   ...: class Body(BaseModel):
   ...:     user_id: int
   ...:     message: str
   ...: 
   ...: OneOrManyMessages = RootModel[Body | list[Body]]

In [3]: get_model_schema(OneOrManyMessages)
Out[3]: 
{'$defs': {'Body': {'properties': {'user_id': {'title': 'User Id',
     'type': 'integer'},
    'message': {'title': 'Message', 'type': 'string'}},
   'required': ['user_id', 'message'],
   'title': 'Body',
   'type': 'object'}},
 'anyOf': [{'$ref': '#/components/schemas/Body'},
  {'items': {'$ref': '#/components/schemas/Body'}, 'type': 'array'}],
 'title': 'RootModel[Union[Body, list[Body]]]'}

In [4]: issubclass(OneOrManyMessages, BaseModel)
Out[4]: True

In [5]: import inspect

In [6]: inspect.isclass(OneOrManyMessages)
Out[6]: True

In [7]: type(OneOrManyMessages)
Out[7]: pydantic._internal._model_construction.ModelMetaclass

[aodj-kara]

I discovered that using OneOrManyMessages.__class__ works though:

from pydantic import BaseModel, RootModel

class Body(BaseModel):
    user_id: int
    message: str

OneOrManyMessages = RootModel[Body | list[Body]]

@app.post("/message")
def send_message(body: OneOrManyMessages.__class__):
    ...

... although I do get an error from Pylance: "Variable not allowed in type expression"

[luolingchun]

@aodj-kara

I recommend a way to write it that meets your needs:

class OneOrManyMessages(RootModel):
    root: Body | list[Body]