FastAPIデータベース統合：非同期データベース操作の深掘り

            pip install fastapi uvicorn[standard]
            

              
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            # Driver for PostgreSQL
pip install asyncpg

# For the SQLAlchemy 2.0+ approach
pip install sqlalchemy

# For the 'databases' library approach
pip install databases[postgresql]
            

              
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            import databases
import sqlalchemy
from fastapi import FastAPI

# --- Database Configuration ---
# Replace with your actual database URL
# Format for asyncpg: "postgresql+asyncpg://user:password@host/dbname"
DATABASE_URL = "postgresql+asyncpg://user:password@localhost/testdb"

database = databases.Database(DATABASE_URL)

# SQLAlchemy model metadata (for table creation)
metadata = sqlalchemy.MetaData()

# Define a sample table
notes = sqlalchemy.Table(
    "notes",
    metadata,
    sqlalchemy.Column("id", sqlalchemy.Integer, primary_key=True),
    sqlalchemy.Column("title", sqlalchemy.String(100)),
    sqlalchemy.Column("content", sqlalchemy.String(500)),
)

# Create an engine for table creation (this part is synchronous)
# The 'databases' library doesn't handle schema creation
engine = sqlalchemy.create_engine(DATABASE_URL.replace("+asyncpg", ""))
metadata.create_all(engine)

# --- FastAPI Application ---
app = FastAPI(title="FastAPI with Databases Library")

@app.on_event("startup")
async def startup():
    print("Connecting to database...")
    await database.connect()
    print("Database connection established.")

@app.on_event("shutdown")
async def shutdown():
    print("Disconnecting from database...")
    await database.disconnect()
    print("Database connection closed.")

# --- API Endpoints ---
@app.get("/")
def read_root():
    return {"message": "Welcome to the Async Database API!"}

            

              
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            from pydantic import BaseModel
from typing import List, Optional

# --- Pydantic Models for data validation ---
class NoteIn(BaseModel):
    title: str
    content: str

class Note(BaseModel):
    id: int
    title: str
    content: str

# --- CRUD Endpoints ---

@app.post("/notes/", response_model=Note)
async def create_note(note: NoteIn):
    """Create a new note in the database."""
    query = notes.insert().values(title=note.title, content=note.content)
    last_record_id = await database.execute(query)
    return {**note.dict(), "id": last_record_id}

@app.get("/notes/", response_model=List[Note])
async def read_all_notes():
    """Retrieve all notes from the database."""
    query = notes.select()
    return await database.fetch_all(query)

@app.get("/notes/{note_id}", response_model=Note)
async def read_note(note_id: int):
    """Retrieve a single note by its ID."""
    query = notes.select().where(notes.c.id == note_id)
    result = await database.fetch_one(query)
    if result is None:
        raise HTTPException(status_code=404, detail="Note not found")
    return result

@app.put("/notes/{note_id}", response_model=Note)
async def update_note(note_id: int, note: NoteIn):
    """Update an existing note."""
    query = (
        notes.update()
        .where(notes.c.id == note_id)
        .values(title=note.title, content=note.content)
    )
    result = await database.execute(query)
    if result == 0:
        raise HTTPException(status_code=404, detail="Note not found")
    return {**note.dict(), "id": note_id}

@app.delete("/notes/{note_id}")
async def delete_note(note_id: int):
    """Delete a note by its ID."""
    query = notes.delete().where(notes.c.id == note_id)
    result = await database.execute(query)
    if result == 0:
        raise HTTPException(status_code=404, detail="Note not found")
    return {"message": "Note deleted successfully"}


            

              
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            from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession
from sqlalchemy.orm import sessionmaker

DATABASE_URL = "postgresql+asyncpg://user:password@localhost/testdb"

# Create an async engine
engine = create_async_engine(DATABASE_URL, echo=True)

# Create a session factory
# expire_on_commit=False prevents attributes from being expired after commit
AsyncSessionLocal = sessionmaker(
    bind=engine, class_=AsyncSession, expire_on_commit=False
)

            

              
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            from sqlalchemy import Column, Integer, String
from sqlalchemy.orm import declarative_base

Base = declarative_base()

class Note(Base):
    __tablename__ = "notes"

    id = Column(Integer, primary_key=True, index=True)
    title = Column(String(100), index=True)
    content = Column(String(500))

            

              
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            from pydantic import BaseModel

class NoteBase(BaseModel):
    title: str
    content: str

class NoteCreate(NoteBase):
    pass

class Note(NoteBase):
    id: int

    class Config:
        orm_mode = True

            

              
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            from fastapi import Depends, FastAPI, HTTPException
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.future import select

from . import models, schemas
from .database import engine, AsyncSessionLocal

app = FastAPI()

# --- Dependency for getting a DB session ---
async def get_db() -> AsyncSession:
    async with AsyncSessionLocal() as session:
        try:
            yield session
        finally:
            await session.close()

# --- Database Initialization (for creating tables) ---
@app.on_event("startup")
async def startup_event():
    print("Initializing database schema...")
    async with engine.begin() as conn:
        # await conn.run_sync(models.Base.metadata.drop_all)
        await conn.run_sync(models.Base.metadata.create_all)
    print("Database schema initialized.")

            

              
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@app.post("/notes/", response_model=schemas.Note)
async def create_note(
    note: schemas.NoteCreate, db: AsyncSession = Depends(get_db)
):
    db_note = models.Note(title=note.title, content=note.content)
    db.add(db_note)
    await db.commit()
    await db.refresh(db_note)
    return db_note

@app.get("/notes/", response_model=list[schemas.Note])
async def read_all_notes(skip: int = 0, limit: int = 100, db: AsyncSession = Depends(get_db)):
    result = await db.execute(select(models.Note).offset(skip).limit(limit))
    notes = result.scalars().all()
    return notes

@app.get("/notes/{note_id}", response_model=schemas.Note)
async def read_note(note_id: int, db: AsyncSession = Depends(get_db)):
    result = await db.execute(select(models.Note).filter(models.Note.id == note_id))
    db_note = result.scalar_one_or_none()
    if db_note is None:
        raise HTTPException(status_code=404, detail="Note not found")
    return db_note

@app.put("/notes/{note_id}", response_model=schemas.Note)
async def update_note(
    note_id: int, note: schemas.NoteCreate, db: AsyncSession = Depends(get_db)
):
    result = await db.execute(select(models.Note).filter(models.Note.id == note_id))
    db_note = result.scalar_one_or_none()
    if db_note is None:
        raise HTTPException(status_code=404, detail="Note not found")
    
    db_note.title = note.title
    db_note.content = note.content
    await db.commit()
    await db.refresh(db_note)
    return db_note

@app.delete("/notes/{note_id}")
async def delete_note(note_id: int, db: AsyncSession = Depends(get_db)):
    result = await db.execute(select(models.Note).filter(models.Note.id == note_id))
    db_note = result.scalar_one_or_none()
    if db_note is None:
        raise HTTPException(status_code=404, detail="Note not found")
    
    await db.delete(db_note)
    await db.commit()
    return {"message": "Note deleted successfully"}

            

              
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            from fastapi.concurrency import run_in_threadpool

@app.get("/run-sync-task/")
async def run_sync_task():
    # 'some_blocking_io_function' is a regular sync function
    result = await run_in_threadpool(some_blocking_io_function, arg1, arg2)
    return {"result": result}

            

              
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            async def transfer_funds():
    async with database.transaction():
        await database.execute(query_for_debit)
        await database.execute(query_for_credit)

            

              
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            async def transfer_funds(db: AsyncSession = Depends(get_db)):
    async with db.begin(): # This starts a transaction
        # Find accounts
        account_from = ...
        account_to = ...
        # Update balances
        account_from.balance -= 100
        account_to.balance += 100
    # The transaction is automatically committed on exiting the block
    # or rolled back if an exception occurs.

            

              
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