How to use PostgreSQL database in FastAPI

from sqlalchemy import Column, DateTime, ForeignKey, Integer, String, Float
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
from sqlalchemy.sql import func
Base  = declarative_base()
class Book(Base):
    __tablename__ = 'book'
    id  = Column(Integer, primary_key=True, index=True)
    title = Column(String)
    rating = Column(Float)
    time_created = Column(DateTime(timezone=True), server_default=func.now())
    time_updated = Column(DateTime(timezone=True), onupdate=func.now())
    author_id = Column(Integer, ForeignKey('author.id'))
    author = relationship('Author')
class Author(Base):
    __tablename__ = 'author'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    age = Column(Integer)
    time_created = Column(DateTime(timezone=True), server_default=func.now())
    time_updated = Column(DateTime(timezone=True), onupdate=func.now())

# build a schema using pydantic
from pydantic import BaseModel
class Book(BaseModel):
    title: str
    rating: int
    author_id: int
    class Config:
        orm_mode = True
class Author(BaseModel):
    name:str
    age:int
    class Config:
        orm_mode = True
        

import uvicorn
from fastapi import FastAPI
from fastapi_sqlalchemy import DBSessionMiddleware, db
from schema import Book as SchemaBook
from schema import Author as SchemaAuthor
from schema import Book
from schema import Author
from models import Book as ModelBook
from models import Author as ModelAuthor
import os
from dotenv import load_dotenv
load_dotenv('.env')
app = FastAPI()
# to avoid csrftokenError
app.add_middleware(DBSessionMiddleware, db_url=os.environ['DATABASE_URL'])
@app.get("/")
async def root():
    return {"message": "hello world"}
@app.post('/book/', response_model=SchemaBook)
async def book(book: SchemaBook):
    db_book = ModelBook(title=book.title, rating=book.rating, author_id = book.author_id)
    db.session.add(db_book)
    db.session.commit()
    return db_book
@app.get('/book/')
async def book():
    book = db.session.query(ModelBook).all()
    return book
  
@app.post('/author/', response_model=SchemaAuthor)
async def author(author:SchemaAuthor):
    db_author = ModelAuthor(name=author.name, age=author.age)
    db.session.add(db_author)
    db.session.commit()
    return db_author
@app.get('/author/')
async def author():
    author = db.session.query(ModelAuthor).all()
    return author
# To run locally
if __name__ == '__main__':
    uvicorn.run(app, host='0.0.0.0', port=8000)

from logging.config import fileConfig
from sqlalchemy import engine_from_config
from sqlalchemy import pool
from alembic import context
# My code
import os,sys
from dotenv import load_dotenv
BASE_DIR= os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
load_dotenv(os.path.join(BASE_DIR, '.env'))
sys.path.append(BASE_DIR)
# This is the Alembic Config object, which provides
# Access to the values within the .ini file in use.
config = context.config
#  Making a connection
config.set_main_option('sqlalchemy.url', os.environ['DATABASE_URL'])
# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)
import models
# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = models.Base.metadata
# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.
def run_migrations_offline():
    """Run migrations in 'offline' mode.
    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.
    Calls to context.execute() here emit the given string to the
    script output.
    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )
    with context.begin_transaction():
        context.run_migrations()
def run_migrations_online():
    """Run migrations in 'online' mode.
    In this scenario we need to create an Engine
    and associate a connection with the context.
    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )
    with connectable.connect() as connection:
        context.configure(
            connection=connection, target_metadata=target_metadata
        )
        with context.begin_transaction():
            context.run_migrations()
if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()