Develop Reference

Return uppercase UUID in FastApi

When using FastApi with a pydantic model at the reponse model, I found that the uuid are always returned lowercase by the http response. Is there any standard way to return them upper cased?
from fastapi import FastAPI
from pydantic import BaseModel
from uuid import UUID
app = FastAPI()
class Test(BaseModel):
ID: UUID
#app.get("/test", response_model=Test)
async def test():
id_ = uuid.uuid4()
return Test(ID=id_)
When making the request the returned uuid will be in lowercased.
from requestr
a = requests.get("http://localhost:800/test").text # you ir
# a -> '{"ID":"fffc0b5b-8e8d-4d06-b910-2ae8d616166c"}' # it is lowercased
The only somewhat hacky way I found to return them uppercased is overwriting the uuid class __str__ method or sub-classing uuid:
What I tried (and works):
# use in main.py when importing for first time
def newstr(self):
hex = '%032x' % self.int
return ('%s-%s-%s-%s-%s' % (hex[:8], hex[8:12], hex[12:16], hex[16:20], hex[20:])).upper()
uuid.UUID.__str__ = newstr
But I was wondering if there is a standard way of doing this without modifying the original class, maybe a post process in pydantic or a setting in FastApi.

You can define custom json_encoders:
class Test(BaseModel):
ID: UUID
class Config:
json_encoders = {
UUID: lambda val: str(val).upper()
}

How to include non-pydantic classes in fastapi responses?

I want to include a custom class into a route's response. I'm mostly using nested pydantic.BaseModels in my application, so it would be nice to return the whole thing without writing a translation from the internal data representation to what the route returns.
As long as everything inherits from pydantic.BaseModel this is trivial, but I'm using a class Foo in my backend which can't do that, and I can't subclass it for this purpose either. Can I somehow duck type that class's definition in a way that fastapi accepts it? What I have right now is essentially this:
main.py
from fastapi import FastAPI
from pydantic import BaseModel
app = FastAPI()
class Foo:
"""Foo holds data and can't inherit from `pydantic.BaseModel`."""
def __init__(self, x: int):
self.x = x
class Response(BaseModel):
foo: Foo
# plus some more stuff that doesn't matter right now because it works
#app.get("/", response_model=Response)
def root():
return Response(foo=Foo(1))
if __name__ == '__main__':
import uvicorn
uvicorn.run("main:app") # RuntimeError

It's not documented, but you can make non-pydantic classes work with fastapi. What you need to do is:
Tell pydantic that using arbitrary classes is fine. It
will try to jsonify them using vars(), so only straight forward
data containers will work - no using property, __slots__ or stuff like that[1].
Create a proxy BaseModel, and tell Foo to offer it if someone
asks for its schema - which is what fastapis OpenAPI pages do.
I'll just assume that you want them to work too since they're
amazing.
main.py
from fastapi import FastAPI
from pydantic import BaseModel, BaseConfig, create_model
app = FastAPI()
BaseConfig.arbitrary_types_allowed = True # change #1
class Foo:
"""Foo holds data and can't inherit from `pydantic.BaseModel`."""
def __init__(self, x: int):
self.x = x
__pydantic_model__ = create_model("Foo", x=(int, ...)) # change #2
class Response(BaseModel):
foo: Foo
#app.get("/", response_model=Response)
def root():
return Response(foo=Foo(1))
if __name__ == '__main__':
import uvicorn
uvicorn.run("main:app") # works
[1] If you want more complex jsonification, you need to provide it to the Response class explicitly via Config.json_encoders.

Here is a full implementation using a subclass with validators and extra schema:
from psycopg2.extras import DateTimeTZRange as DateTimeTZRangeBase
from sqlalchemy.dialects.postgresql import TSTZRANGE
from sqlmodel import (
Column,
Field,
Identity,
SQLModel,
)
from pydantic.json import ENCODERS_BY_TYPE
ENCODERS_BY_TYPE |= {DateTimeTZRangeBase: str}
class DateTimeTZRange(DateTimeTZRangeBase):
#classmethod
def __get_validators__(cls):
yield cls.validate
#classmethod
def validate(cls, v):
if isinstance(v, str):
lower = v.split(", ")[0][1:].strip().strip()
upper = v.split(", ")[1][:-1].strip().strip()
bounds = v[:1] + v[-1:]
return DateTimeTZRange(lower, upper, bounds)
elif isinstance(v, DateTimeTZRangeBase):
return v
raise TypeError("Type must be string or DateTimeTZRange")
#classmethod
def __modify_schema__(cls, field_schema):
field_schema.update(type="string", example="[2022,01,01, 2022,02,02)")
class EventBase(SQLModel):
__tablename__ = "event"
timestamp_range: DateTimeTZRange = Field(
sa_column=Column(
TSTZRANGE(),
nullable=False,
),
)
class Event(EventBase, table=True):
id: int | None = Field(
default=None,
sa_column_args=(Identity(always=True),),
primary_key=True,
nullable=False,
)
as per #Arne 's solution you need to add your own validators and schema if the Type you are using has __slots__ and basically no way to get out a dict.
Link to Github issue: https://github.com/tiangolo/sqlmodel/issues/235#issuecomment-1162063590

FastAPI query parameter using Pydantic model

I have a Pydantic model as below
class Student(BaseModel):
name:str
age:int
With this setup, I wish to get the OpenAPI schema as following,
So, how can I use the Pydantic model to get the from query parameter in FastAPI?

You can do something like this,
from fastapi import FastAPI, Depends
from pydantic import BaseModel
app = FastAPI()
class Student(BaseModel):
name: str
age: int
#app.get("/")
def read_root(student: Student = Depends()):
return {"name": student.name, "age": student.age}
Also, note that the query parameters are usually "optional" fields and if you wish to make them optional, use Optional type hint as,
from fastapi import FastAPI, Depends
from typing import Optional
from pydantic import BaseModel
app = FastAPI()
class Student(BaseModel):
name: str
age: Optional[int]
#app.get("/")
def read_root(student: Student = Depends()):
return {"name": student.name, "age": student.age}

Python class utcnow not updating

I have setup a simple class in Python with a member posted that defaults to utcnow() time as a string. However when I create an instance of the class then create another instance a few minutes later they both have the exact same posted time.
If in the route I have created I pass in posted=str(datetime.utcnow()) it works fine so Python is picking up the computer datetime correctly. I have also tested this on a Heroku app I have running and I get the same problem.
The time it puts in is the time the app was first run as if it's being treated as a static value.
import uuid
from datetime import datetime
from typing import Dict
from dataclasses import dataclass, field
from models.model import Model
#dataclass
class Dummy(Model):
collection: str = field(init=False, default='dummy')
text: str
posted: str = field(default=str(datetime.utcnow()))
_id: str = field(default_factory=lambda: uuid.uuid4().hex)
def json(self) -> Dict:
return {
"text": self.text,
"posted": self.posted,
"_id": self._id
}

You could use default_factory instead in case you want a dynamically default value.
#dataclass
class Dummy(Model):
...
posted: str = field(default_factory=lambda: str(datetime.utcnow()))

Is it possible to modify Pydantic BaseModel attributes just after creating it?

I am starting to learn FastAPI and Pydantic and have a doubt. I have the following subclass of BaseModel
class Product(BaseModel):
image: str
name: str
After saving this model, I want image to store the value /static/ + image so as to create nice hyperlinked REST endpoint. This is possible using __post_init_post_parse__ hook of pydantic dataclass but since FastAPI currently doesn't support it, I was wondering what can be a workaround this.

You could use a custom validator:
>>> from pydantic import BaseModel, validator
>>> class Product(BaseModel):
image: str
name: str
#validator('image')
def static_mage(cls, image):
return '/static/{}'.format(image)
>>> p = Product(image='pic.png', name='product_1')
>>> p
Product(image='/static/pic.png', name='product_1')