fastapi-dev

FastAPI Development

Project Context — Read project-config.md in the repo root for brand tokens, shared-library paths, and deployment targets.

When to Use

Invoke this skill when:

• Creating a new FastAPI backend for a project
• Adding API endpoints for Streamlit frontends
• Implementing repository pattern with SQL Server
• Setting up dependency injection chains
• Configuring CORS for Streamlit ↔ FastAPI communication
• Deploying FastAPI on IIS/on-premise infrastructure

---

Project Structure

backend/
├── app/
│   ├── __init__.py
│   ├── main.py              # FastAPI application entry
│   ├── config.py            # Settings (pydantic-settings)
│   ├── dependencies.py      # Shared DI providers
│   ├── routers/
│   │   ├── __init__.py
│   │   ├── records.py        # Records endpoints
│   │   └── analytics.py     # Analytics endpoints
│   ├── models/
│   │   ├── __init__.py
│   │   ├── record.py         # Pydantic request/response models
│   │   └── user.py
│   ├── services/
│   │   ├── __init__.py
│   │   └── record_service.py
│   └── repositories/
│       ├── __init__.py
│       └── record_repo.py
├── tests/
├── .env
└── requirements.txt

---

Steps

Step 1: Configuration (pydantic-settings)

# app/config.py
from functools import lru_cache
from pydantic_settings import BaseSettings
from pydantic import Field

class Settings(BaseSettings):
    app_name: str = "API"
    debug: bool = False
    db_server: str = Field(..., description="SQL Server host")
    db_name: str = Field(..., description="Database name")
    db_password: str = Field(..., repr=False)
    api_key: str = Field(..., repr=False)
    allowed_origins: list[str] = ["http://localhost:8501"]
    ollama_base_url: str = "http://localhost:11434"
    ollama_model: str = "llama3.1"

    class Config:
        env_file = ".env"

@lru_cache
def get_settings() -> Settings:
    return Settings()

Step 2: Pydantic Models (Base/Create/Update/Response pattern)

# app/models/record.py
from pydantic import BaseModel, ConfigDict, Field
from uuid import UUID
from datetime import datetime
from typing import Literal

class RecordBase(BaseModel):
    customer_id: str = Field(..., min_length=1, max_length=50, example="CUST001")
    record_type: Literal["billing", "service", "technical"]
    description: str = Field(..., min_length=10, max_length=5000)
    priority: int = Field(default=3, ge=1, le=5)

class RecordCreate(RecordBase):
    pass

class RecordUpdate(BaseModel):
    status: Literal["open", "in_progress", "resolved"] | None = None
    resolution_notes: str | None = Field(None, max_length=2000)
    priority: int | None = Field(None, ge=1, le=5)

class RecordResponse(RecordBase):
    model_config = ConfigDict(from_attributes=True)
    id: UUID
    status: str
    created_at: datetime
    updated_at: datetime | None = None

class RecordList(BaseModel):
    items: list[RecordResponse]
    total: int
    page: int
    per_page: int
    pages: int