FastAPI - how to generate random ID?

Question

I'm making simple CRUD API using FastAPI and what I want to do is generate unique random when creating new item (other fields are address and name which should be filled by user). How can I do that?

There is fragment of my code with class and a POST function.

app = FastAPI()

userdb = []

class User(BaseModel):
    id: int
    address: str
    name: str

@app.post("/users")
def add_user(user: User):
    userdb.append(users.dict())
    return userdb[-1]

Answer 1

uuid4 is often the way to go

It'll be absolutely unique amongst any id ever generated with the function anywhere with astronomical likelihood (refer to RFC-4122 Section 4.4 ) and is very fast

from uuid import uuid4

...
    unique_id = str(uuid4())

Answer 2

Another option - often what you want is for this ID to not necessarily be random, but rather to be some auto-incremented index from your database. The FastAPI docs give an example of this:

...

notes = sqlalchemy.Table(
    "notes",
    metadata,
    sqlalchemy.Column("id", sqlalchemy.Integer, primary_key=True),
    sqlalchemy.Column("text", sqlalchemy.String),
    sqlalchemy.Column("completed", sqlalchemy.Boolean),
)

...
class NoteIn(BaseModel):
    text: str
    completed: bool

class Note(BaseModel):
    id: int
    text: str
    completed: bool

...

@app.post("/notes/", response_model=Note)
async def create_note(note: NoteIn):
    query = notes.insert().values(text=note.text, completed=note.completed)
    last_record_id = await database.execute(query)
    return {**note.dict(), "id": last_record_id}

https://fastapi.tiangolo.com/advanced/async-sql-databases/?h=id#about-notedict-id-last_record_id

In your case you would use separate models for UserIn and User . Then in your example you would then assign the ID in the response model as the index in your userdb list (which in a real app would probably not just be a list, but a database).

from fastapi import FastAPI
from pydantic import BaseModel

app = FastAPI()

userdb = []

class UserIn(BaseModel):
    address: str
    name: str

class User(BaseModel):
    id: int
    address: str
    name: str

@app.post("/users")
def add_user(user_in: UserIn) -> User:
    userdb.append(user_in)
    user_out_dict = userdb[-1].dict()
    user_out_dict.update({"id": len(userdb)-1})
    return User(**user_out_dict)