Looping many to many response in a many to many response in fastapi

[nzivo]

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Example Code

#user schema
from typing import List, Optional
from app.schemas.RBAC.resource import ResourceInDBBase

from pydantic import BaseModel, EmailStr


# Shared properties
class UserBase(BaseModel):
    email: Optional[EmailStr] = None
    is_active: Optional[bool] = True
    is_superuser: bool = False
    full_name: Optional[str] = None
    first_name: Optional[str] = None
    last_name: Optional[str] = None
    phone: Optional[int] = None
    user_metadata: Optional[str] = None



# Properties to receive via API on creation
class UserCreate(UserBase):
    email: EmailStr
    password: str


# Properties to receive via API on update
class UserUpdate(UserBase):
    password: Optional[str] = None
    first_name: Optional[str] = None
    last_name: Optional[str] = None
    phone: Optional[int] = None
    user_metadata: Optional[str] = None
    is_active: Optional[bool] = True
    is_superuser: bool = None


class UserInDBBase(UserBase):
    id: int
    resources: List[ResourceInDBBase]

    class Config:
        orm_mode = True
        allow_population_by_field_name = True


# Additional properties to return via API
class User(UserInDBBase):
    pass


# Additional properties stored in DB
class UserInDB(UserInDBBase):
    hashed_password: str

#resource schema
from typing import List, Optional
from app.schemas.RBAC.role import RoleInDBBase

from pydantic import BaseModel

# Shared properties
class ResourceBase(BaseModel):
    resource_title: Optional[str] = None
    resource_slug: Optional[str] = None
    resource_description: Optional[str] = None

# Properties to receive via API on creation
class ResourceCreate(ResourceBase):
    resource_title: str
    resource_slug: str
    resource_description: str

# Properties to receive on Resource update
class ResourceUpdate(ResourceBase):
    resource_title: Optional[str] = None
    resource_slug: Optional[str] = None
    resource_description: Optional[str] = None

# Properties shared by models stored in DB
class ResourceInDBBase(ResourceBase):
    id: int
    roles: List[RoleInDBBase]

    class Config:
        orm_mode = True
        allow_population_by_field_name = True

# Properties to return to client
class Resource(ResourceInDBBase):
    pass

# Properties properties stored in DB
class ResourceInDB(ResourceInDBBase):
    pass

#role schema
from typing import List, Optional
from app.schemas.RBAC.permission import PermissionInDBBase

from pydantic import BaseModel

# Shared properties
class RoleBase(BaseModel):
    role_title: Optional[str] = None
    role_slug: Optional[str] = None
    role_description: Optional[str] = None

# Properties to receive via API on creation
class RoleCreate(RoleBase):
    role_title: str
    role_slug: str
    role_description: str

# Properties to receive on Role update
class RoleUpdate(RoleBase):
    role_title: Optional[str] = None
    role_slug: Optional[str] = None
    role_description: Optional[str] = None

# Properties shared by models stored in DB
class RoleInDBBase(RoleBase):
    id: int

    class Config:
        orm_mode = True
        allow_population_by_field_name = True

# Properties to return to client
class Role(RoleInDBBase):
    pass

# Properties properties stored in DB
class RoleInDB(RoleInDBBase):
    pass

Description

I have a fastapi application with 3 entities in the database that have a many to many relationship in a cascading way. Users have many resources and vice versa, resources have many roles and vice versa, I am wondering if it is possible to get a user entry and then list resources attached to it and roles attached to the resource? I have so far managed to display resources for the user but roles returns an empty list,

my schemas are defined in pydantic and sqlachemy for my models

[ { "email": "user@example.com", "is_active": true, "is_superuser": false, "full_name": "string", "first_name": "string", "last_name": "string", "phone": 0, "user_metadata": "string", "id": 0, "resources": [ { "resource_title": "string", "resource_slug": "string", "resource_description": "string", "id": 0, "roles": [] } ] } ]

The error from my docker is as follows
INFO: 172.26.0.6:56558 - "GET /api/v1/users/?skip=0&limit=100 HTTP/1.1" 500 Internal Server Error
ERROR: Exception in ASGI application
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/uvicorn/protocols/http/httptools_impl.py", line 390, in run_asgi
result = await app(self.scope, self.receive, self.send)
File "/usr/local/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in call
return await self.app(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/fastapi/applications.py", line 146, in call
await super().call(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/applications.py", line 102, in call
await self.middleware_stack(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/middleware/errors.py", line 181, in call
raise exc from None
File "/usr/local/lib/python3.8/site-packages/starlette/middleware/errors.py", line 159, in call
await self.app(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/middleware/cors.py", line 76, in call
await self.app(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/exceptions.py", line 82, in call
raise exc from None
File "/usr/local/lib/python3.8/site-packages/starlette/exceptions.py", line 71, in call
await self.app(scope, receive, sender)
File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 550, in call
await route.handle(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 227, in handle
await self.app(scope, receive, send)
File "/usr/local/lib/python3.8/site-packages/starlette/routing.py", line 41, in app
response = await func(request)
File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 204, in app
response_data = await serialize_response(
File "/usr/local/lib/python3.8/site-packages/fastapi/routing.py", line 126, in serialize_response
raise ValidationError(errors, field.type)
pydantic.error_wrappers.ValidationError: 2 validation errors for User
response -> 0 -> resources -> 0 -> roles
field required (type=value_error.missing)
response -> 2 -> resources -> 0 -> roles
field required (type=value_error.missing)

Operating System

Linux, Windows

Operating System Details

This is a docker container application, the original fullstack mysql fastapi

FastAPI Version

0.54.1

Python Version

3.8

Additional Context

No response

[odiseo0]

Probably you're returning the wrong response, try returning it raw to see what are you sending, also I recommend you to update the version of FastAPI

[nzivo]

@odiseo0 I have updated all dependencies but I still get the same error

[sploitfaze]

I reproduced the same error by this code:

from typing import List

from pydantic import BaseModel


class Resource(BaseModel):
    roles: List[str]


class User(BaseModel):
    resources: List[Resource]


def main() -> None:
    User(
        resources=[
            {},
            {"roles": []},
            {},
        ]
    )


if __name__ == '__main__':
    main()

And got the next error:

...
    raise validation_error
pydantic.error_wrappers.ValidationError: 2 validation errors for User
resources -> 0 -> roles
  field required (type=value_error.missing)
resources -> 2 -> roles
  field required (type=value_error.missing)

So, the reason of such error could be missing roles field, or it is equals to None.

Solution 1

You cloud make roles optional. Like this:

class Resource(BaseModel):
    roles: Optional[List[str]]

It sets roles field to None even it is not provided at all.

Solution 2 (Preferable)

I would recommend to use default_factory property like this:

from pydantic import BaseModel, Field

class Resource(BaseModel):
    roles: List[str] = Field(default_factory=list)

But notice that default_factory property is available only since pydantic==1.5 (fullstack mysql fastapi has pydantic==1.4)

[nzivo]

Thank you @leonidpodriz it worked. I also noticed, declaring the relatable pydantic models also helped in one file