FastAPI Config Patterns

Reusable Pydantic settings classes for FastAPI applications with common configuration patterns.

Extracted from: GridFlow backend/src/config.py

Installation

pip install fastapi-config-patterns

Features

• BaseFastAPISettings: Common FastAPI app settings (debug, host, port, CORS)
• BaseDatabaseSettings: Database connection configuration mixin
• Validators: Reusable field validators (CORS origins parser)

Usage

Basic Settings

from fastapi_config_patterns import BaseFastAPISettings

class Settings(BaseFastAPISettings):
    # Add your app-specific settings
    app_name: str = "my-app"
    secret_key: str

settings = Settings()
print(settings.debug)  # False
print(settings.port)   # 8000

With Database

from fastapi_config_patterns import (
    BaseFastAPISettings,
    BaseDatabaseSettings
)

class Settings(BaseFastAPISettings, BaseDatabaseSettings):
    app_name: str = "my-app"

settings = Settings()
print(settings.database_url)  # postgresql+asyncpg://...

CORS Origins Validator

from pydantic import field_validator
from pydantic_settings import BaseSettings
from fastapi_config_patterns import assemble_cors_origins

class Settings(BaseSettings):
    allowed_origins: list[str]
    
    @field_validator("allowed_origins", mode="before")
    @classmethod
    def parse_origins(cls, v):
        return assemble_cors_origins(v)

# From environment variable: ALLOWED_ORIGINS="http://localhost:3000,http://localhost:8080"
settings = Settings()
print(settings.allowed_origins)  # ["http://localhost:3000", "http://localhost:8080"]

Environment Variables

The base classes support these environment variables:

# BaseFastAPISettings
DEBUG=true
ALLOWED_ORIGINS="http://localhost:3000,http://localhost:8080"

# BaseDatabaseSettings
DATABASE_URL="postgresql+asyncpg://user:pass@localhost:5432/db"

API Reference

BaseFastAPISettings

Base settings class with common FastAPI configuration.

Fields:

• debug (bool): Debug mode (default: False, env: DEBUG)
• api_v1_str (str): API v1 prefix (default: "/v1")
• host (str): Server host (default: "0.0.0.0")
• port (int): Server port (default: 8000)
• allowed_origins (Union[str, List[str]]): CORS origins
• cors_allow_credentials (bool): Allow credentials (default: False)
• cors_max_age (int): Preflight cache seconds (default: 600)

BaseDatabaseSettings

Database connection configuration mixin.

Fields:

• database_url (str): Database connection URL (env: DATABASE_URL)

Supported databases:

• PostgreSQL: postgresql+asyncpg://user:pass@host:port/db
• SQLite: sqlite+aiosqlite:///./app.db

assemble_cors_origins(v)

Parse CORS origins from string or list.

Args:

• v (Union[str, List[str]]): Origins as string or list

Returns:

• List[str]: Parsed list of origins

Handles:

• Wildcard "*" for all origins
• Comma-separated string
• List of strings

Dependencies

• pydantic>=2.0.0
• pydantic-settings>=2.0.0

License

MIT