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

Installation

Install Metro using pip:

pip install metroapi

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

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

Scaffold Generator Options

metro generate scaffold NAME [FIELDS...] [OPTIONS]

Available Options:

--actions, -a (multiple): Define additional custom routes beyond CRUD operations

Format: http_method:path (query: params) (body: params) (desc: description) (action_name: action_name)
Example: -a "get:search (query: term:str) (desc: Search users) (action_name: search_users)"

--exclude-crud, -x (multiple): Specify which CRUD operations to exclude

Choices: index, show, create, update, delete
Example: -x delete -x update

--model-inherits: Specify base class(es) for the model

Format: Single class or comma-separated list
Example: --model-inherits UserBase or --model-inherits "UserBase,SomeMixin"

--controller-inherits: Specify base class(es) for the controller

Format: Single class or comma-separated list
Example: --controller-inherits AdminController

--before-request, --before (multiple): Add lifecycle hooks to run before each request

Format: hook_name or hook_name:description
Example: --before "check_admin:Verify admin access"

--after-request, --after (multiple): Add lifecycle hooks to run after each request

Format: hook_name or hook_name:description
Example: --after "log_action:Log all activities"

Advanced Usage Examples

Full CRUD scaffold with search and custom actions:

metro generate scaffold Product name:str price:float \
  -a "get:search (query: term:str,min_price:float,max_price:float) (desc: Search products) (action_name: search_products)" \
  -a "post:bulk-update (body: ids:list,price:float) (desc: Update multiple products) (action_name: bulk_update_products)"

Scaffold with limited CRUD and inheritance:

metro generate scaffold AdminUser email:str role:str \
  --model-inherits "UserBase,AuditableMixin" \
  --controller-inherits AdminController \
  -x delete \
  --before "check_admin:Verify admin permissions" \
  --after "log_admin_action:Log admin activities"

Custom API endpoints with complex parameters:

metro generate scaffold Order items:list:ref:Product status:str \
  -a "post:process/{id} (body: payment_method:str) (desc: Process order payment) (action_name: process_order)" \
  -a "get:user/{user_id} (query: status:str,date_from:datetime) (desc: Get user orders) (action_name: get_user_orders)"
  --controller-inherits "BaseController,PaymentMixin"

Adding Custom Routes

Use the --actions or -a option to add additional routes beyond the standard CRUD endpoints:

ex.

metro generate scaffold Comment post_id:ref:Post author:str content:str --actions "post:reply"
# or
metro generate scaffold Post title:str body:str -a "post:publish" -a "get:drafts"

This will generate the standard CRUD routes plus two additional routes:

POST /posts/publish
GET /posts/drafts

Excluding CRUD Routes

Use the --exclude-crud or -x option to exclude specific CRUD routes you don't need:

metro generate scaffold Post title:str body:str -x delete -x update

This will generate a scaffold without the delete and update endpoints.

You can combine both options:

metro generate scaffold Post title:str body:str -a "post:publish" -x delete

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

Model Generator Options

metro generate model NAME [FIELDS...] [OPTIONS]

Available Options:

--model-inherits: Specify base class(es) for the model

Format: Single class or comma-separated list
Example: --model-inherits UserBase or --model-inherits "UserBase,SomeMixin"

Example with all options:

metro generate model User email:str password:hashed_str profile:ref:Profile roles:list:str --model-inherits "UserBase"

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

Controller Generator Options

metro generate controller NAME [ACTIONS...] [OPTIONS]

Available Options:

--controller-inherits: Specify base class(es) for the controller

Format: Single class or comma-separated list
Example: --controller-inherits AdminController

--before-request, --before (multiple): Add lifecycle hooks to run before each request

Format: hook_name or hook_name:description
Example: --before "check_auth:Verify user authentication"

--after-request, --after (multiple): Add lifecycle hooks to run after each request

Format: hook_name or hook_name:description
Example: --after "log_request:Log API request"

Example with all options:

metro generate controller Auth \
  "post:login (body: email:str,password:str) (desc: User login)" \
  "post:register (body: email:str,password:str,name:str) (desc: User registration)" \
  "post:reset-password/{token} (body: password:str) (desc: Reset password)" \
  --controller-inherits AuthBaseController \
  --before "rate_limit:Apply rate limiting" \
  --after "log_auth_attempt:Log authentication attempt"

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

? and ^are used to define a field as optional or unique respectively.

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.

Field Choices:

For string fields that should only accept specific values, use the choices syntax with optional default value (marked with *):

# required role with no default value (role must be specified)
metro generate model User role:string:choices[user,admin]

# optional role with default value of 'user'
metro generate model User role:string:choices[user*,admin]  # note it would be redundant to add ? here since the default value makes it optional

You can combine these modifiers to create fields with multiple attributes:

metro generate model Product \
  sku^:str \                                  # unique identifier 
  name^:str \                                 # unique name
  price:float \                               # no modifier makes price required
  description?:str \                          # optional description
  status:string:choices[active*,discontinued] # enum with default value

Indexes:

Use the --index flag to create indexes for more efficient querying. The syntax supports various MongoDB index options:

Note that built in timestamp fields like created_at, updated_at, and deleted_at are automatically indexed and don't need to be specified.

# Basic single field index
metro generate model User email:str --index "email"

# Basic compound index
metro generate model Product name:str price:float --index "name,price"

# Unique compound index
metro generate model Product name:str price:float --index "name,price[unique]"

# Compound index with descending order and sparse option
metro generate model Order total:float --index "created_at,total[desc,sparse]"  # note that created_at is a built-in field so it doesn't need to be defined explicitly

You can specify multiple compound indexes:

metro generate model Product \
  name:str \
  price:float \
  category:str \
  --index "name,price[unique]" \
  --index "category,created_at[desc,sparse]"

This will generate:

class Product(BaseModel):
    name = StringField(required=True)
    price = FloatField(required=True)
    category = StringField(required=True) 
    created_at = DateTimeField(required=True)

    meta = {
        "collection": "product",
        'indexes': [
            {
                'fields': ['name', 'price'],
                'unique': True
            },
            {
                'fields': ['-category', '-created_at'],
                'sparse': True
            }
        ],
    }

Index Options:

unique: Ensures no two documents can have the same values for these fields
sparse: Only includes documents in the index if they have values for all indexed fields
desc: Creates the index in descending order (useful for sorting)

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"

Controllers

Controllers handle incoming HTTP requests and define the behavior of your API endpoints. Metro provides a simple, decorator-based routing system similar to Flask or FastAPI.

Basic Controller

from metro.controllers import Controller, Request, get, post, put, delete

class UsersController(Controller):
    meta = {
        'url_prefix': '/users'  # Optional URL prefix for all routes in this controller
    }

    @get("/")
    async def index(self, request: Request):
        return {"users": []}
    
    @post("/")
    async def create(self, request: Request):
        user_data = await request.json()
        return {"message": "User created"}
    
    ...

Request Parameters

from metro import Controller, Request, Body, Query, Path

class ProductsController(Controller):
    @get("/search")
    async def search(
        self,
        request: Request,
        query: str,               # Query parameter (?query=...)
        category: str = None,     # Optional query parameter
        page: int = 1,           # Query parameter with default value
    ):
        return {"results": []}

    @post("/{id}/reviews")
    async def add_review(
        self,
        request: Request,
        id: str,                 # Path parameter
        rating: int = Body(...), # Body parameter (required)
        comment: str = Body(None) # Optional body parameter
    ):
        return {"message": "Review added"}

Response Types

Controllers can return various types of responses:

from metro.responses import JSONResponse, HTMLResponse, RedirectResponse

class ContentController(Controller):
    @get("/data")
    async def get_data(self, request: Request):
        # Automatically converted to JSON
        return {"data": "value"}
    
    @get("/page")
    async def get_page(self, request: Request):
        # Explicit HTML response
        return HTMLResponse("<h1>Hello World</h1>")
    
    @get("/old-path")
    async def redirect(self, request: Request):
        # Redirect response
        return RedirectResponse("/new-path")

Error Handling

Metro provides standard exceptions for common HTTP error cases:

from metro.exceptions import NotFoundError, BadRequestError, UnauthorizedError

class ArticlesController(Controller):
    @get("/{id}")
    async def show(self, request: Request, id: str):
        article = None  # Replace with actual lookup
        if not article:
            raise NotFoundError(detail="Article not found")
        return article

    @post("/")
    async def create(self, request: Request):
        data = await request.json()
        if "title" not in data:
            raise BadRequestError(detail="Title is required")
        return {"message": "Article created"}

Directory-Based URL Prefixes

Metro automatically generates URL prefixes based on your controller's location in the directory structure. This helps organize your API endpoints logically:

app/controllers/
├── users_controller.py          # Routes will be at /
├── api/
│   ├── v1/
│   │   ├── posts_controller.py  # Routes will be at /api/v1
│   │   └── tags_controller.py   # Routes will be at /api/v1
│   └── v2/
│       └── posts_controller.py  # Routes will be at /api/v2
└── admin/
    └── users_controller.py      # Routes will be at /admin

For example:

# app/controllers/api/v1/posts_controller.py
class PostsController(Controller):
    @get("/")          # Final URL: /api/v1/posts
    async def index(self, request: Request):
        return {"posts": []}

    @get("/{id}")      # Final URL: /api/v1/posts/{id}
    async def show(self, request: Request, id: str):
        return {"post": {"id": id}}

    # You can still add your own prefix that combines with the directory prefix
    meta = {
        'url_prefix': '/blog'  # Routes will be at /api/v1/blog
    }

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="[email protected]",
    recipients=["[email protected]"],
    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.

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

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

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.

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"

Conductor

"If the Rails generator was powered by an LLM"

Configuring API Keys for Conductor

Add your OpenAI/Anthropic API keys to power Conductor

metro conductor setup add-key

metro conductor setup list-keys

metro conductor setup remove-key

Initializing a New Project

Generate the starter code for a Metro project from a project description using the init command:

metro conductor init <project_name> <description>

ex.

metro conductor init my-app "A social media app where users can make posts, comment, like, and share posts, and follow other users."

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.

License

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

Name		Name	Last commit message	Last commit date
Latest commit History 39 Commits
conductor		conductor
docs		docs
metro		metro
.gitignore		.gitignore
LICENSE		LICENSE
README.md		README.md
project_to_txt.py		project_to_txt.py
pyproject.toml		pyproject.toml
requirements.txt		requirements.txt
setup.py		setup.py

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Metro

Features

Installation

Creating a New Project

Starting the Development Server

Scaffolding Resources

Scaffold Generator Options

Available Options:

Advanced Usage Examples

Adding Custom Routes

Excluding CRUD Routes

Generating Models and Controllers

Generating a Model

Model Generator Options

Available Options:

Generating a Controller

Controller Generator Options

Available Options:

Field types

Basic Field Types:

Special Field Types:

Defining Model Relationships

Field Modifiers

Optional Field:

Unique Field:

Field Choices:

Indexes:

Index Options:

Specialty Field Types

Hashed Field

File Fields

File Storage Configuration

Controllers

Basic Controller

Request Parameters

Response Types

Error Handling

Directory-Based URL Prefixes

For example:

Controller Lifecycle Hooks

Example: AdminController and AdminUserController

Key Points:

Execution:

Rate Limiting

Throttling Controller Endpoints:

Throttling Routes

Customizing Rate Limiting

Email Sending

SMS Sending

Database Management

Starting a Local MongoDB Instance

Stopping the Local MongoDB Instance

Running MongoDB in a Docker Container

Configuration

Admin Panel

Conductor

Configuring API Keys for Conductor

Initializing a New Project

Documentation and Help

License

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