first commit

app/database.py

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+"""
+Database configuration and session management for async PostgreSQL.
+
+Uses SQLAlchemy 2.0 async ORM with asyncpg driver.
+"""
+
+from typing import AsyncGenerator
+
+from sqlalchemy.ext.asyncio import (
+    AsyncSession,
+    async_sessionmaker,
+    create_async_engine,
+)
+from sqlalchemy.orm import DeclarativeBase
+
+from app.core.config import get_settings
+
+settings = get_settings()
+
+# Create async engine with connection pooling
+engine = create_async_engine(
+    settings.DATABASE_URL,
+    echo=settings.ENVIRONMENT == "development",  # Log SQL in development
+    pool_pre_ping=True,  # Verify connections before using
+    pool_size=10,  # Number of connections to maintain
+    max_overflow=20,  # Max additional connections beyond pool_size
+    pool_recycle=3600,  # Recycle connections after 1 hour
+)
+
+# Create async session factory
+AsyncSessionLocal = async_sessionmaker(
+    engine,
+    class_=AsyncSession,
+    expire_on_commit=False,  # Prevent attributes from being expired after commit
+    autocommit=False,
+    autoflush=False,
+)
+
+
+class Base(DeclarativeBase):
+    """Base class for all database models."""
+
+    pass
+
+
+async def get_db() -> AsyncGenerator[AsyncSession, None]:
+    """
+    Dependency for getting async database session.
+
+    Yields:
+        AsyncSession: Database session
+
+    Example:
+        ```python
+        @app.get("/items/")
+        async def get_items(db: AsyncSession = Depends(get_db)):
+            result = await db.execute(select(Item))
+            return result.scalars().all()
+        ```
+    """
+    async with AsyncSessionLocal() as session:
+        try:
+            yield session
+            await session.commit()
+        except Exception:
+            await session.rollback()
+            raise
+        finally:
+            await session.close()
+
+
+async def init_db() -> None:
+    """
+    Initialize database - create all tables.
+
+    Note: In production, use Alembic migrations instead.
+    This is useful for development and testing.
+    """
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+
+
+async def close_db() -> None:
+    """Close database connections."""
+    await engine.dispose()