Add FastAPI pub/sub example with real-world PGMQ usage patterns

.github/workflows/examples.yml

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+name: Examples Tests
+
+on:
+  push:
+    branches: [main, develop]
+    paths:
+      - 'examples/**'
+      - 'examples_tests/**'
+      - 'pgmq_sqlalchemy/**'
+      - '.github/workflows/examples.yml'
+  pull_request:
+    branches: [main, develop]
+    paths:
+      - 'examples/**'
+      - 'examples_tests/**'
+      - 'pgmq_sqlalchemy/**'
+      - '.github/workflows/examples.yml'
+
+jobs:
+  test-examples:
+    runs-on: ubuntu-latest
+
+    permissions:
+      contents: read
+
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
+
+    name: Test Examples (Python ${{ matrix.python-version }})
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Install uv
+        run: |
+          curl -LsSf https://astral.sh/uv/install.sh | sh
+          echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+      - name: Install dependencies
+        run: |
+          uv sync --extra dev
+          # Install additional dependencies for examples
+          uv pip install fastapi uvicorn httpx
+
+      - name: Start PostgreSQL
+        run: |
+          cp pgmq_postgres.template.env pgmq_postgres.env
+          cp pgmq_tests.template.env pgmq_tests.env
+          make start-db
+
+      - name: Setup database for examples tests
+        run: |
+          docker compose exec -T pgmq_postgres psql -U postgres -c "CREATE EXTENSION IF NOT EXISTS pgmq CASCADE;"
+
+      - name: Run examples tests
+        run: |
+          uv run pytest examples_tests --cov=examples --cov-report=xml:coverage-examples-py${{ matrix.python-version }}.xml -v
+
+      - name: Upload coverage artifact
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-examples-py${{ matrix.python-version }}
+          path: coverage-examples-py${{ matrix.python-version }}.xml
+          retention-days: 1
+
+      - name: Cleanup
+        if: always()
+        run: |
+          docker compose down

examples/fastapi_pub_sub/README.md

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+# FastAPI Pub/Sub Example with PGMQ
+
+This example demonstrates a real-world scenario of using PGMQ with FastAPI for an order management system. It shows how to:
+
+- Use PGMQ with FastAPI and sync SQLAlchemy sessions (psycopg2)
+- Publish messages using `PGMQOperation` (op) in a web API
+- Consume messages asynchronously using `PGMQueue` with asyncpg
+
+## Architecture
+
+- **API Server (api.py)**: FastAPI application that creates orders and publishes them to PGMQ
+  - Uses sync database driver (psycopg2)
+  - Uses `PGMQOperation` (imported as `op`) for publishing messages
+  - Provides REST endpoints for creating and retrieving orders
+
+- **Consumer (consumer.py)**: Async worker that processes orders from the queue
+  - Uses async database driver (asyncpg)
+  - Uses `PGMQueue` class for reading messages
+  - Processes messages concurrently with asyncio
+
+## Prerequisites
+
+- PostgreSQL with PGMQ extension installed
+- Python 3.9 or higher
+
+Quick setup:
+```bash
+docker run -d --name postgres -e POSTGRES_PASSWORD=postgres -p 5432:5432 quay.io/tembo/pg16-pgmq:latest
+```
+
+## Installation
+
+Install required dependencies:
+
+```bash
+pip install -r requirements.txt
+```
+
+## Running the Example
+
+### 1. Start the API Server
+
+```bash
+python api.py
+```
+
+The API will be available at http://localhost:8000
+
+### 2. Start the Consumer
+
+In a separate terminal:
+
+```bash
+python consumer.py
+```
+
+### 3. Create Orders
+
+Create an order via the API:
+
+```bash
+curl -X POST "http://localhost:8000/orders" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "customer_name": "John Doe",
+    "product_name": "Widget",
+    "quantity": 5,
+    "price": 29.99
+  }'
+```
+
+You should see:
+- The API returns the created order with a message ID
+- The consumer logs show the order being processed
+
+### 4. View Order
+
+Get an order by ID:
+
+```bash
+curl "http://localhost:8000/orders/1"
+```
+
+## API Endpoints
+
+- `POST /orders` - Create a new order
+- `GET /orders/{order_id}` - Get order by ID
+- `GET /health` - Health check endpoint
+
+## How It Works
+
+1. When an order is created via the API:
+   - The order is saved to the database
+   - A message is published to PGMQ using `op.send()`
+   - The message contains order details
+
+2. The consumer:
+   - Continuously polls the queue for new messages
+   - Processes messages concurrently using asyncio
+   - Deletes successfully processed messages
+   - Leaves failed messages in the queue for retry
+
+## Configuration
+
+You can modify the following constants in the files:
+
+- `DATABASE_URL`: PostgreSQL connection string
+- `QUEUE_NAME`: Name of the PGMQ queue (default: "order_queue")
+- `batch_size`: Number of messages to process in each batch (consumer.py)
+- `vt`: Visibility timeout in seconds (consumer.py)

examples/fastapi_pub_sub/api.py

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+"""FastAPI API server for Order management with PGMQ message publishing.
+
+This example demonstrates:
+- Using FastAPI with SQLAlchemy sync session (psycopg2)
+- Publishing messages to PGMQ using PGMQOperation (op)
+- Creating orders and sending them to a message queue
+"""
+from typing import Generator
+from contextlib import contextmanager, asynccontextmanager
+
+from fastapi import FastAPI, Depends, HTTPException
+from pydantic import BaseModel, ConfigDict
+from sqlalchemy import create_engine, Column, Integer, String, Float, DateTime
+from sqlalchemy.orm import Session, sessionmaker, declarative_base
+from datetime import datetime
+
+from pgmq_sqlalchemy import op
+
+# Database configuration
+DATABASE_URL = "postgresql+psycopg2://postgres:postgres@localhost:5432/postgres"
+QUEUE_NAME = "order_queue"
+
+# SQLAlchemy setup
+engine = create_engine(DATABASE_URL)
+SessionLocal = sessionmaker(bind=engine, autocommit=False, autoflush=False)
+Base = declarative_base()
+
+
+# Order Model (SQLAlchemy ORM)
+class Order(Base):
+    __tablename__ = "orders"
+
+    id = Column(Integer, primary_key=True, index=True)
+    customer_name = Column(String, nullable=False)
+    product_name = Column(String, nullable=False)
+    quantity = Column(Integer, nullable=False)
+    price = Column(Float, nullable=False)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+
+# Pydantic models for request/response
+class OrderCreate(BaseModel):
+    customer_name: str
+    product_name: str
+    quantity: int
+    price: float
+
+
+class OrderResponse(BaseModel):
+    model_config = ConfigDict(from_attributes=True)
+
+    id: int
+    customer_name: str
+    product_name: str
+    quantity: int
+    price: float
+    created_at: datetime
+    message_id: int
+
+
+# Lifespan context manager for startup/shutdown
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    """Initialize database tables and PGMQ queue on startup."""
+    # Startup
+    Base.metadata.create_all(bind=engine)
+
+    # Initialize PGMQ queue
+    with SessionLocal() as session:
+        op.check_pgmq_ext(session=session, commit=True)
+
+        # Create queue if it doesn't exist
+        try:
+            op.create_queue(QUEUE_NAME, session=session, commit=True)
+        except Exception:
+            # Queue might already exist, which is fine
+            pass
+
+    yield
+
+    # Shutdown (if needed)
+
+
+# FastAPI app with lifespan
+app = FastAPI(title="Order Management with PGMQ", lifespan=lifespan)
+
+# Database dependency
+def get_db() -> Generator[Session, None, None]:
+    """Database session dependency."""
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+
+@app.post("/orders", response_model=OrderResponse, status_code=201)
+def create_order(order_data: OrderCreate, db: Session = Depends(get_db)):
+    """Create a new order and publish it to the message queue.
+
+    Args:
+        order_data: Order information
+        db: Database session
+
+    Returns:
+        Created order with message ID
+    """
+    # Create order in database
+    db_order = Order(
+        customer_name=order_data.customer_name,
+        product_name=order_data.product_name,
+        quantity=order_data.quantity,
+        price=order_data.price,
+    )
+    db.add(db_order)
+    db.commit()
+    db.refresh(db_order)
+
+    # Publish message to PGMQ using op
+    message_data = {
+        "order_id": db_order.id,
+        "customer_name": db_order.customer_name,
+        "product_name": db_order.product_name,
+        "quantity": db_order.quantity,
+        "price": db_order.price,
+        "created_at": db_order.created_at.isoformat(),
+    }
+
+    msg_id = op.send(QUEUE_NAME, message_data, session=db, commit=True)
+
+    # Return order with message ID
+    return OrderResponse(
+        id=db_order.id,
+        customer_name=db_order.customer_name,
+        product_name=db_order.product_name,
+        quantity=db_order.quantity,
+        price=db_order.price,
+        created_at=db_order.created_at,
+        message_id=msg_id,
+    )
+
+
+@app.get("/orders/{order_id}", response_model=OrderCreate)
+def get_order(order_id: int, db: Session = Depends(get_db)):
+    """Get order by ID.
+
+    Args:
+        order_id: Order ID
+        db: Database session
+
+    Returns:
+        Order information
+    """
+    order = db.query(Order).filter(Order.id == order_id).first()
+    if not order:
+        raise HTTPException(status_code=404, detail="Order not found")
+    return order
+
+
+@app.get("/health")
+def health_check():
+    """Health check endpoint."""
+    return {"status": "ok"}
+
+
+if __name__ == "__main__":
+    import uvicorn
+    uvicorn.run(app, host="0.0.0.0", port=8000)