main.py

from fastapi import FastAPI
from pydantic import BaseModel, validator, BaseConfig
from geoalchemy2 import WKTElement
from geoalchemy2.shape import to_shape

"""Minimum working example snippet for handling lat lng coordinates and geometry types using Fastapi"""

app = FastAPI()


class Coordinates(BaseModel):
    lat: float = 0
    lng: float = 0

    @validator('lat')
    def lat_within_range(cls, v):
        if not -90 < v < 90:
            raise ValueError('Latitude outside allowed range')
        return v
        
    @validator('lng')
    def lng_within_range(cls, v):
        if not -180 < v < 180:
            raise ValueError('Longitude outside allowed range')
        return v

class UserIn(BaseModel):
    username: str
    coordinates: Coordinates

class UserOut(BaseModel):
    username: str
    coordinates: Coordinates

class UserInDB(BaseModel):
    username: str
    coordinates_geom: WKTElement

    class Config(BaseConfig):
        arbitrary_types_allowed = True

def get_geom_from_coordinates(coordinates: Coordinates):
    geom_wkte = WKTElement(f"Point ({coordinates.lng} {coordinates.lat})", srid=4326, extended=True)
    return geom_wkte

def get_coordinates_from_geom(geom: WKTElement):
    shply_geom = to_shape(geom)
    coordinates = Coordinates(lng=shply_geom.x, lat=shply_geom.y)
    return coordinates

def fake_save_user(user_in: UserIn):
    coordinates_geom = get_geom_from_coordinates(user_in.coordinates)
    user_in_db = UserInDB(**user_in.dict(), coordinates_geom=coordinates_geom)
    print("User saved! ..not really")
    return user_in_db

def fake_loaduser(user_saved: UserInDB):
    coordinates = get_coordinates_from_geom(user_saved.coordinates_geom)
    user_out = UserOut(**user_saved.dict(), coordinates=coordinates)
    print("User loaded! ..not really")
    return user_out
    
@app.post("/user/", response_model=UserOut)
async def create_user(*, user_in: UserIn):
    user_saved = fake_save_user(user_in)
    user_out = fake_loaduser(user_saved)
    return user_out