Metro

Metro is a lightweight, opinionated, batteries-included Python web framework built on top of FastAPI and MongoEngine.
It is means to provide helpful, lightweight abstractions to enable standard ways of implementing common patters to prevent the SaaSification of the developer stack.

The goal is to enhance not inhibit.

Features

• Built on top of FastAPI and MongoEngine ODM
• CLI tool for project management and code generation
• Built-in database management (MongoDB)
• Support for both local and Docker-based development
• Environment-specific configurations
• Automatic API documentation

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Installation

Install Metro using pip:

pip install metroapi

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Creating a New Project

Create a new Metro project using the new command:

metro new my_project
cd my_project

This will create a new directory my_project with the default project structure:

my_project/
├── app/
│   ├── controllers/
│   ├── models/
│   └── __init__.py
├── config/
│   ├── development.py
│   ├── production.py  
│   └── __init__.py
├── main.py
├── Dockerfile
└── docker-compose.yml

---

Starting the Development Server

Start the development server using the run command:

metro run

This will start the development server on http://localhost:8000.

You can also run the service using Docker:

metro run --docker

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Scaffolding Resources

Metro includes a scaffold generator to quickly create models, controllers, and route definitions for a new resource.

To generate a scaffold for a Post resource with title and body fields:

metro generate scaffold Post title:str body:str

This will generate:

• app/models/post.py with a Post model class
• app/controllers/posts_controller.py with CRUD route handlers
• Update app/controllers/__init__.py to import the new controller
• Update app/models/__init__.py to import the new model

Generating Models and Controllers

You can also generate models and controllers individually.

Generating a Model

To generate a Comment model with post_id, author, and content fields:

metro generate model Comment post_id:str author:str content:str

Generating a Controller

To generate a controller for Auth routes:

metro generate controller Auth

You can also pass in the routes to generate as arguments:

metro generate controller Auth post:login post:register

Field types

Basic Field Types:

str, int, float, bool, datetime, date, dict, list.

Special Field Types:

ref, file, list:ref, list:file, hashed_str.

Defining Model Relationships

You can define relationships between models using the following syntax:

• One-to-Many Relationship: Use the ref: prefix followed by the related model name.

metro generate model Post author:ref:User

This will generate a Post model with an author field referencing the User model.

• Many-to-Many Relationship: Use list: and ref: together.

metro generate model Student courses:list:ref:Course

This will generate a Student model with a courses field that is a list of references to Course models.

Field Modifiers

_, ^ are used to define a field as optional or unique.

Optional Field:

Append _ to the field name to mark it as optional.

metro generate model User email_:str

This will generate a User model with an optional email field.

Unique Field:

Append ^ to the field name to specify it as unique.

metro generate model User username^:str

This will generate a User model with a unique username field.

Specialty Field Types

Hashed Field

hashed_str is a special field type that automatically hashes the value before storing it in the database.

metro generate model User name:str password_hashed:str

This will generate a User model with a password field stored as a hashed value.

File Fields

file and list:file are special field types for handling file uploads. They automatically upload files to the specified storage backend (local filesystem, AWS S3, etc.) and store the file path and file metadata in the database.

• file: Generates a single FileField on the model.
• list:file: Generates a FileListField, allowing multiple files.

Example usage:

metro generate model User avatar:file
metro generate model Post attachments:list:file

This will generate the following model classes:

class User(BaseModel):
    avatar = FileField()
    
class Post(BaseModel):
    attachments = FileListField()

Uploading files to s3 then becomes as easy as:

# Set an individual file field
@put('/users/{id}/update-avatar')
async def update_avatar(
    self,
    id: str,
    avatar: UploadFile = File(None),
):
    user = User.find_by_id(id=id)
    if avatar:
        # This stages the file for upload
        user.avatar = avatar
        # This actually uploads the file and stores the metadata in the database
        user.save()
    
    return user.to_dict()

# Work with a list of files 
@post('/posts/{id}/upload-attachments')
async def upload_attachments(
    self,
    id: str,
    attachments: List[UploadFile] = File(None),
):
    post = Post.find_by_id(id=id)
    if attachments:
        # This stages the new files for upload
        post.attachments.extend(attachments)
        # This actually uploads the files and adds appends to the attachments list in the db with the new metadata
        post.save()
    
    return post.to_dict()

File Storage Configuration

The default configuration is set to use the local filesystem and store files in the uploads directory. You can change the storage backend and location in the config/development.py or config/production.py file.

Default configuration:

FILE_STORAGE_BACKEND = "filesystem"
FILE_SYSTEM_STORAGE_LOCATION = "./uploads"
FILE_SYSTEM_BASE_URL = "/uploads/"

Custom configuration in config/development.py or config/production.py:

FILE_STORAGE_BACKEND = 'filesystem'
FILE_SYSTEM_STORAGE_LOCATION = './uploads_dev'
FILE_SYSTEM_BASE_URL = '/uploads_dev/'

Or to use AWS S3:

FILE_STORAGE_BACKEND = 's3'
S3_BUCKET_NAME = "my-bucket"
AWS_ACCESS_KEY_ID = "..."
AWS_SECRET_ACCESS_KEY = "..."
AWS_REGION_NAME = "us-east-1"

---

Controller Lifecycle Hooks

Lifecycle hooks like before_request and after_request can be defined directly in a controller or inherited from a parent controller. Hooks are useful for tasks such as authentication, logging, or cleanup.

Example: AdminController and AdminUserController

admin_controller.py

from metro.controllers import Controller, before_request, after_request
from metro.exceptions import UnauthorizedError
from metro import Request

class AdminController(Controller):
    @before_request
    async def check_admin(self, request: Request):
        is_admin = False  # Replace with actual logic
        print("Checking admin status... (this will be run before each request)")
        if not is_admin:
            raise UnauthorizedError(detail="Unauthorized access.")

    @after_request
    async def cleanup_stuff(self, request: Request):
        print("Cleaning up... (this will be run after each request)")

admin_user_controller.py

from app.controllers.admin_controller import AdminController

class AdminUserController(AdminController):
    @get('/admin-user/all-users')
    async def all_users(self, request):
        return {"users": []}

Key Points:

• Hooks like check_admin and after_request can be defined directly in a controller or inherited from a parent.
• In AdminUserController, hooks are inherited from AdminController and run before and after each request handler.

Execution:

• If a before_request hook raises an exception (e.g., UnauthorizedError), the request handler is skipped, but the after_request hook still runs.

---

Rate Limiting

Metro includes a built-in rate limiter that can be applied to specific routes or controllers.

Throttling Controller Endpoints:

To apply rate limiting to a controller endpoint, use the @throttle decorator:

from metro.rate_limiting import throttle

class UserController(Controller):
    @get('/users/{id}')
    @throttle(per_second=1, per_minute=10)
    async def get_user(self, request: Request, id: str):
        return {"id": id}

Throttling Routes

To apply rate limiting to a specific route, pass the Throttler class as a dependency:

from metro.rate_limiting import Throttler

@app.get("/users/{id}", dependencies=[Depends(Throttler(per_second=1, per_minute=10))]
async def get_user(request: Request, id: str):
    return {"id": id}

Customizing Rate Limiting

Parameters:

• name: Namespace for the rate limiter.
• limits: Compound rate limit definition. Can be a RateLimits() object or a function that returns a RateLimits() object.
• per_second: Number of requests allowed per second.
• per_minute: Number of requests allowed per minute.
• per_hour: Number of requests allowed per hour.
• per_day: Number of requests allowed per day.
• per_week: Number of requests allowed per week.
• per_month: Number of requests allowed per month.
• backend: Rate limiting backend (e.g., InMemoryRateLimiterBackend, RedisRateLimiterBackend). Defaults to InMemoryRateLimiterBackend.
• callback: Callback function to execute when the rate limit is exceeded. (request, limited, limit_info) => .... Defaults to raising a TooManyRequestsError if limit is exceeded.
• key: Custom key function to generate a unique key for rate limiting. (request) => str. Defaults to request IP.
• cost: Custom cost function to calculate the cost of a request. (request) => int. Defaults to 1.

---

Email Sending

Easily send emails using the built-in EmailSender class, which supports multiple email providers like Mailgun and AWS SES.

# 1. Configure the provider:
# - For Mailgun
mailgun_provider = MailgunProvider(
    domain=os.getenv("MAILGUN_DOMAIN"), api_key=os.getenv("MAILGUN_API_KEY")
)
mailgun_sender = EmailSender(provider=mailgun_provider)

# - For AWS SES (coming soon)
ses_provider = AWSESProvider(region_name="us-west-2")
ses_sender = EmailSender(provider=ses_provider)

# 2. Send the email:
mailgun_sender.send_email(
    source="sender@example.com",
    recipients=["recipient@example.com"],
    subject="Test Email",
    body="This is a test email sent using Mailgun.",
)

---

SMS Sending

Easily send SMS messages using the built-in SMSSender class, which supports multiple SMS providers like Twilio and Vonage.

1. Add the provider credentials to the environment variables or config file:

# For Twilio
TWILIO_ACCOUNT_SID=ACXXXXXXXXXXXXXXXX
TWILIO_AUTH_TOKEN=your_auth_token
TWILIO_PHONE_NUMBER=+1234567890

# For Vonage
VONAEG_API_KEY=your_api_key
VONAGE_API_SECRET=your_api_secret
VONAGE_PHONE_NUMBER=+1234567890

2. Send an SMS message:

sms_sender = SMSSender()  # provider will be automatically detected based on environment variables but can also be specified explicitly

sms_sender.send_sms(
    source="+1234567890",
    recipients=["+1234567891"],
    message="This is a test SMS message!",
)

---

Database Management

Metro provides commands to manage your MongoDB database.

Starting a Local MongoDB Instance

To start a local MongoDB instance for development:

metro db up

Stopping the Local MongoDB Instance

To stop the local MongoDB instance:

metro db down

Running MongoDB in a Docker Container

You can also specify the environment and run MongoDB in a Docker container:

metro db up --env production --docker

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Configuration

Environment-specific configuration files are located in the config directory:

• config/development.py
• config/production.py

Here you can set your DATABASE_URL, API keys, and other settings that vary between environments.

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Admin Panel

Metro includes a built-in admin panel. You can view this at /admin

You can disable this or change the admin route in the config/development.py or config/production.py file:

ENABLE_ADMIN_PANEL = False
ADMIN_PANEL_ROUTE_PREFIX = "/admin-panel"

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Documentation and Help

• API Documentation: http://localhost:8000/docs
• CLI help: metro --help

For guides, tutorials, and detailed API references, check out the Metro documentation site.

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License

Metro is open-source software licensed under the MIT license.