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Check out “Designing Lucky: Rock Solid Actions & Routing” to see how Lucky can make writing your applications reliable and productive with its unique approach to HTTP and routing.

# Routing with Actions

Instead of having separate definition files for routes and controllers, Lucky combines them in action classes. This allows for solid error detection, as well as method and helper creation.

Most Lucky actions use a “REST” style convention. If you’re unfamiliar with REST, you can read our RESTful action guide.

# Example route

To see what a simple action looks like, let’s generate an index action for showing users with lucky gen.action.browser Users::Index.

# src/actions/users/
class Users::Index < BrowserAction
  get "/users" do
    # `plain_text` sends plain/text to the client
    plain_text "Rendering something in Users::Index"

Routes can be defined for specific request types by using the get, put, post, patch, trace, and delete macros. Each Action class must only implement one route.

If you still need access to different methods like options, you can use the match macro.

# src/actions/profile/
class Profile::Show < BrowserAction
  # Respond to an `HTTP OPTIONS` request
  match :options, "/profile" do
    # action code here

Note that lucky gen.action.browser is used to create actions that should be shown in a browser. Whereas lucky gen.action.api is used for actions meant to be used for an API (e.g. JSON).

# Root page

By default Lucky generates a Home::Index action that handles the root path "/". This is the action that renders the Lucky welcome page when you first run lucky dev.

Change Home::Index to redirect to whatever action you want:

# src/actions/home/
class Home::Index < BrowserAction
  include Auth::AllowGuests

  get "/" do
    if current_user?
      redirect Me::Show
      # When you're ready change this line to:
      #   redirect SignIns::New
      # Or maybe show signed out users a marketing page:
      #   html Marketing::IndexPage
      html Lucky::WelcomePage

It may seem strange to redirect as soon as the users visits “/”, but it comes in handy later on. It makes it easy to redirect to different places depending on who the user is. For example, if a user is an admin you may want to redirect them to the Admin::Dashboard::Show action, and if they’re a regular user you may want to take them to the regular dashboard at Dashboard::Show.

# Path parameters

When defining an explicit path, you may mark parts of the path with a :, to have a method generated that returns that param in the action.

# src/actions/users/
class Users::Show < BrowserAction
  get "/users/:some_user_id" do
    plain_text "Requested user id: #{some_user_id}"

Here, the string from the request path will be returned by the some_user_id method. So in this example if /users/123-foo is requested some_user_id would return 123-foo, and the action would return a text response of Requested user id: 123-foo.

# You can use as many parameters as you want

Every named parameter will have a method generated for it so that you can access the value. You can have as many as you want.

For example, delete "/projects/:project_id/tasks/:task_id" would have a project_id and task_id method generated on the class for accessing the named parameters.

# Optional path parameters

Sometimes it can be helpful to allow optional parameters in a route’s path. We can accomplish this by prefixing a path parameter with a ?, like this:

# src/actions/posts/
class Posts::Index < BrowserAction
  get "/posts/:year/:month/?:day" do
    if day
      plain_text "I'll show all posts on a specific day!"
      plain_text "I'll show all posts in a given month!"

In the above example, we require that the Posts::Index route has both a :year and :month provided, but allow users to optionally route to a specific :day as well.

# Understanding RESTful routes

REST is a way to make access to resources more uniform. It consists of the following actions:

  • Index - show a list of resources
  • Show - show one instance of a resource
  • New - typically used to render a form to create a resource
  • Create - create a resource. Usually means saving data to the database
  • Edit - typically used to render a form to edit an existing resource
  • Update - update an existing resource
  • Delete - delete the resource

The word “resource” generally just refers to some model (i.e. User, or BlogPost, etc…)

# Examples of restful routes

For standard resources:

Action Class Route
Users::Index get "/users"
Users::Show get "/users/:user_id"
Users::New get "/users/new"
Users::Create post "/users"
Users::Edit get "/users/:user_id/edit"
Users::Update put "/users/:user_id"
Users::Delete delete "/users/:user_id"
Api::V1::Users::Show get "/api/v1/users/:user_id"
MyAdminSection::Users::Show get "/my_admin_section/users/:user_id"

For nested resources:

Action Class Route
Projects::Users::Index get "/projects/:project_id/users"
Projects::Users::Show get "/projects/:project_id/users/:user_id"
Projects::Users::New get "/projects/:project_id/users/new"
Projects::Users::Create post "/projects/:project_id/users"
Projects::Users::Edit get "/projects/:project_id/users/:user_id/edit"
Projects::Users::Update put "/projects/:project_id/users/:user_id"
Projects::Users::Delete delete "/projects/:project_id/users/:user_id"
Api::V1::Projects::Users::Show get "/api/v1/projects/:project_id/users/:user_id"
MyAdminSection::Projects::Users::Show get "/my_admin_section/projects/:project_id/users/:user_id"

# Fallback routing

For some apps you may want a wildcard/catch-all behavior instead of rendering some HTML when Lucky can’t find a route. For example, this type of behavior can be useful for Single Page Applications (SPAs) so that you can handle routing client-side.

To do this, use the fallback macro.

# in src/actions/frontend/
class Frontend::Index < BrowserAction
  fallback do
    if html?
      html Home::IndexPage

The fallback should always contain a Lucky::RouteNotFoundError error. This is to throw a 404 when an asset, or some other file is not found.

# Routing prefix

Sometimes you need a group of routes to be prefixed with some path. For example, starting all of your routes with /api/v1/. For this, you can use the route_prefix macro.

# src/actions/
abstract class ApiAction < Lucky::Action
  accepted_formats [:json], default: :json

  route_prefix "/api/v1"

Now all of your actions that inherit from ApiAction will start with /api/v1.

class Api::Posts::Index < ApiAction

  # GET /api/v1/posts
  get "/posts" do

class Posts::Index < BrowserAction
  # This is NOT prefixed because it inherits from
  # BrowserAction.
  # GET /posts
  get "/posts" do
    html IndexPage

# Optional and Glob paths

# Optional route paths

You may have a path that has an optional path segment. For example:

# MenuItems::Index

# also MenuItems::Index

In this example, the /appetizers path segment might be optional, but if it does exist, then you are able to change what is displayed on your page. Both routes go to the same Action class.

The optional path param is specified the same as a normal path param, but with a ? prefix. (e.g. /?:path_param)

class MenuItems::Index < BrowserAction
  get "/menu-items/?:section" do
    if section
      # we have a value for section
      # no value for section

# Glob routing

Glob routing is a way to define a path with an unknown number of path segments. This allows you to do deep nested linking, or use different paths for loading specific data. For example:

# Posts::Index

# also Posts::Index

Similar to the optional path segments, but with an unknown number. This can also be used as a “catch-all” route similar to the fallback routing.

To use the glob route, your trailing path segment must be a *. This will give you a method glob that returns a String of the entire trailing path.

class Posts::Index < BrowserAction
  get "/posts/*" do
    if glob
      # glob == "2022/02/14"
      # the path was just "/posts"

You can also name your glob by giving it a path param.

class Posts::Index < BrowserAction
  get "/posts/*:date" do
    if date
      # date == "2022/02/14"
      # the path was just "/posts"

# Routing style

By default Lucky ensures that all routes adhere to the same style. All route paths are expected to use underscores unless you opt-out or change the style check. You can opt-out from style checking by including Lucky::SkipRouteStyleCheck in your action.

# src/actions/users/
class Guides::GettingStarted < BrowserAction
  include Lucky::SkipRouteStyleCheck

  get "/guides/getting-started" do
    plain_text "Get started"

Or, skipping checking altogether by removing Lucky::EnforceUnderscoredRoute from src/actions/

Similarly, a custom style check can be added by adding the enforce_route_style macro in your action. Or, for all actions by adding it to src/actions/ See Lucky::EnforceUnderscoredRoute for an example.

# Memoization

As your application gets larger, you may need to write helper methods that run expensive calculations, or queries. Calling these methods multiple times can lead to performance issues. To mitigate these, you can use the memoize macro.

class Reports::Show < BrowserAction
  get "/report" do
    small_number = calculate_numbers
    big_number = calculate_numbers + 1000
    html ShowPage, small_number: small_number, big_number: big_number

  memoize def calculate_numbers : Int64
    # This is ran only the first time it's called

Memoized methods can return any value, includingnil or false. You can also pass arguments to your memoized method.

class Users::Show < BrowserAction
  get "/users/:id" do
    user = fetch_user(id)

    if user
      html ShowPage, user: user
      redirect to: Home::IndexPage

  # This is only called once per `id` passed in.
  memoize def fetch_user(id : String) : User
    make_api_call &&

If you need access to memoize from outside of your action, just include Lucky::Memoizable.

Learn more about memoization.

# 404 errors

By default Lucky will respond with a 404 when neither a route nor a static file in public is found. You can change what is rendered in Errors::Show which is found in src/actions/errors/

You’ll see a method like this that handles when a route is not found:

# in src/actions/errors/
# Customize this however you want!
def render(error : Lucky::RouteNotFoundError)
  if json?
    error_json "Not found", status: 404
    error_html "Sorry, we couldn't find that page", status: 404

Learn more about error handling.

# Handling parameters

Parameters, or params, are data that is sent from client back to the server. There are a few different ways this can happen:

  • Path parameters - The dynamic values passed in your route path. e.g. /users/:id.
  • Query parameters - The query string at the end of a URL after the ? in key/value pairs. e.g. ?page=1
  • Form parameters - Data sent through HTTP POST. This may be formatted as JSON.
  • Multipart parameters - Similar to form parameters, but generally to contain a file.

# Type-safe query params

You may want to accept parameters in the query string, e.g. /users?page=2. Lucky gives you access to these in a type-safe way through the param macro.

# src/actions/users/
class Users::Index < BrowserAction
  param page : Int32 = 1

  get "/users" do
    plain_text "All users starting on page #{page}"

When you add a query parameter with the param macro, it will generate a method for you to access the value. The parameter definition will inspect the given type declaration, so you can easily define required or optional parameters by using non- or nilable types (Int32 vs. Int32?). Parameter defaults are set by assigning a value in the parameter definition. Query parameters are type-safe as well, so when /users?page=unlucky is accessed with the above definition, an exception is raised.

Just like path parameters, you can define as many query parameters as you want. Every query parameter will have a method generated for it to access the value.

To pass these params from a page in to the action, you will use the with method.

def content
  link "View more users", to: Users::Index.with(page: 2)

Read more on link generation

# Params from query string

You also have access to these with the params method.

Here’s an example of using parameters when visiting the /users?page=1&filter=active path:

# src/actions/users/
class Users::Index < BrowserAction

  get "/users" do
    filter = params.get(:filter) # type String
    page = params.get(:page) # type String
    per = params.get(:per) # Error! there is no parameter :per

    plain_text "All users starting on page #{page}"

The params.get?(:key) method will return nil if the key doesn’t exist instead of raising an error.

get "/users" do
  per = params.get?(:per) # returns nil

  plain_text "..."

By default, all param values are trimmed of blankspace. If you need the raw value, use params.get_raw(:key) or params.get_raw?(:key).

The from_query method returns HTTP::Params from query params. You can access the values similar to a Hash(String, String).

# /path?q=Lucky
params.from_query["q"] #=> "Lucky"
params.from_query["search"] #=> Error!
params.from_query["search"]? #=> nil

This is the same as using params.get_raw(:key) and params.get_raw?(:key).

# Params from JSON

Parses the request body as JSON::Any or raises Lucky::ParamParsingError if JSON is invalid.

# {"users": [{"name": "Skyler"}]}
params.from_json["users"][0]["name"].as_s #=> "Skyler"

# Params from form data

The from_form_data method returns HTTP::Params from x-www-form-urlencoded body params.


# Params from multipart

Returns multipart params and files in a Tuple(Hash(String, String), Hash(String, Lucky::UploadedFile)).

form_params = params.from_multipart.first # Hash(String, String)
form_params["name"]                      # "Kyle"

files = params.from_multipart.last # Hash(String, Lucky::UploadedFile)
files["avatar"]                    # Lucky::UploadedFile

params.get_file(:avatar)    # Lucky::UploadedFile
params.get_file?("missing") # nil

# Arrays in params

When it comes to a collection of values in params, there’s no official standard for how this should be formatted. For this reason, each framework must choose on their own how to handle it. For Lucky, we’ve gone with the square bracket notation key[]=value1&key[]=value2.

To access these values as an Array(String), you can use the get_all(:key), or get_all?(:key) methods.

# key[]=value1&key[]=value2
params.get_all(:key)  # ["value1", "value2"]

params.get_all?("missing") # nil

# Nested params

When data is sent through HTML forms, Lucky will namespace or “nest” the parameter names according to the object used in the form. For example, if we’re saving a User object, all of the param names will be prefixed with user:. (i.e. user:name, user:email).

To access these values, we can use the params.nested(:key) and params.nested?(:key) methods.

class Users::Create < BrowserAction
  # user:name=Alesia&user:age=35&page=1
  post "/users" do
    data = params.nested(:user)
    name = data["name"] #=> "Alesia"
    email = data["email"]? #=> nil

    plain_text "The name is #{name}"

Lucky also gives you the ability to send more than 1 set of param values at the same time. We call the many_nested.

In this example, we want to create 2 notes at the same time.

# notes[0]:title=Buying&notes[1]:title=Selling
class Notes::Create < BrowserAction
  post "/notes" do
    notes = params.many_nested(:notes)

    plain_text "The first note title is #{notes[0]["title"]}"

The many_nested method will raise an error if the key does not exist. Use many_nested?(:key) to return nil in that case.

# Nested files

For files associated with models, the param will be nested. (e.g. post:banned_photo) To access the file from the nested params, use the nested_file or nested_file? methods.

params.nested_file(:post)       # Lucky::UploadedFile
params.nested_file?("missing")  # nil

# Debugging Params

If you need to get the raw params, you can call params.body which will take the request, and give you a String of what params were sent. { {raw_params: params.body} }

# Convert params to a Hash(String, String | Hash(String, String))

# Subdomains

Sometimes you want to require that an endpoint is called with a subdomain. For example, you might have endpoints you only expose in the test environment which is called with a subdomain. That would allow to work but would raise a Lucky::InvalidSubdomainError.

To specify and require subdomains, you need to include Lucky::Subdomain in your action or in the class your action inherits. For example, in src/actions/

Once included, you use require_subdomain

# subdomain required but can be anything

# subdomain required and must equal "admin"
require_subdomain "admin"

# subdomain required and must match regex
require_subdomain /(dev|qa|prod)/

# subdomain required and must match one of the items in the array
require_subdomain ["tenant1", "tenant2", /tenantd/]

When that is used, you can then access the subdomain by calling subdomain in your route handler. Even if you don’t require a subdomain, you can still call subdomain? to check if one was provided, but keep in mind that it will be nilable.

get "/admin" do
  subdomain #=> compile time error if `require_subdomain` not specified, guaranteed to return a String otherwise
  subdomain? #=> can be called without `require_subdomain`, but will return String | Nil

# Where to put actions

Actions go in src/actions and follow the structure of the class.

For example Users::Show would go in src/actions/users/ and Api::V1::Users::Delete would go in src/actions/api/v1/users/

See a problem? Have an idea for improvement? Edit this page on GitHub