If you want to follow along yourself, you will need the following things:
1. Elixir and Erlang installed
2. A text editor to make the changes that we make
3. A terminal to run the commands we show using `iex`
## Steps
For this tutorial, we'll use examples based around creating a help desk.
We will make the following resources:
-`Helpdesk.Tickets.Ticket`
-`Helpdesk.Tickets.Representative`
-`Helpdesk.Tickets.Customer`
The actions we will be able to take on these resources include:
- Opening a new ticket
- Closing a ticket
- Assigning a ticket to a representative
### Create a new project
We first create a new project with the `--sup` flag to add a supervision tree. This will be necessary for later steps.
```bash
# In your terminal
mix new --sup helpdesk && cd helpdesk
```
It is a good idea to make it a git repository and commit the initial project. You'll be able to see what changes we made, and can save your changes once we're done.
```bash
# Run in your terminal
git init
git add -A
git commit -m "init"
```
Open the project in your text editor, and we'll get started.
### Add Ash to your application
Add the ash dependency to your `mix.exs`
{{mix_dep:ash}}
Add ash to your .formatter.exs file
```elixir
[
# import the formatter rules from ash
import_deps: [:ash],
inputs: [...]
]
```
And run `mix deps.get`
### Creating our first resources
The basic building blocks of an Ash application are resources. They are tied together by an API module (not to be confused with a web API), which will allow you to interact with those resources.
Lets start by creating our first resource along with our first API. We will create the following files:
- The API - `lib/helpdesk/tickets.ex`
- A registry to list our resources - `lib/helpdesk/tickets/registry.ex`
# Add a set of simple actions. You'll customize these later.
defaults [:create, :read, :update, :destroy]
end
# Attributes are the simple pieces of data that exist on your resource
attributes do
# Add an autogenerated UUID primary key called `:id`.
uuid_primary_key :id
# Add a string type attribute called `:subject`
attribute :subject, :string
end
end
```
```elixir
# lib/helpdesk/tickets/registry.ex
defmodule Helpdesk.Tickets.Registry do
use Ash.Registry,
extensions: [
# This extension adds helpful compile time validations
Ash.Registry.ResourceValidations
]
entries do
entry Helpdesk.Tickets.Ticket
end
end
```
```elixir
# lib/helpdesk/tickets.ex
defmodule Helpdesk.Tickets do
use Ash.Api
resources do
# This defines the set of resources that can be used with this API
registry Helpdesk.Tickets.Registry
end
end
```
### Try our first resource out
Run `iex -S mix` in your project and try it out
To create a ticket, we first make an `Ash.Changeset` for the `:create` action of the `Helpdesk.Tickets.Ticket` resource. Then we pass it to the `create!/1` function on our API module `Helpdesk.Tickets`.
```elixir
Helpdesk.Tickets.Ticket
|> Ash.Changeset.for_create(:create)
|> Helpdesk.Tickets.create!()
```
This returns what we call a `record` which is an instance of a resource.
```elixir
{:ok, #Helpdesk.Tickets.Ticket<
...,
id: "c0f8dc32-a018-4eb4-8656-d5810118f4ea",
subject: nil,
...
>}
```
### Customizing our Actions
One thing you may have noticed earlier is that we created a ticket without providing any input, and as a result our ticket had a `subject` of `nil`. Additionally, we don't have any other data on the ticket. Lets add a `status` attribute, ensure that `subject` can't be `nil`, and provide a better interface by making a custom action for opening a ticket, called `:open`.
We'll start with the attribute changes:
```elixir
attributes do
...
attribute :subject, :string do
# Don't allow `nil` values
allow_nil? false
end
# status is either `open` or `closed`. We can add more statuses later
attribute :status, :atom do
# Constraints allow you to provide extra rules for the value.
# The available constraints depend on the type
# See the documentation for each type to know what constraints are available
# Since atoms are generally only used when we know all of the values
# it provides a `one_of` constraint, that only allows those values
constraints [one_of: [:open, :closed]]
# The status defaulting to open makes sense
default :open
# We also don't want status to ever be `nil`
allow_nil? false
end
end
```
And then add our customized action:
```elixir
actions do
...
create :open do
# By default you can provide all public attributes to an action
# This action should only accept the subject
accept [:subject]
end
end
```
Now we can play with these changes in iex:
We use `create!` with an exclamation point here because that will raise the error which gives a nicer view of the error in `iex`
```elixir
# Use this to pick up changes you've made to your code, or restart your session
recompile()
Helpdesk.Tickets.Ticket
|> Ash.Changeset.for_create(:open, %{subject: "My mouse won't click!"})
|> Helpdesk.Tickets.create!()
```
And we can see our newly created ticket with a subject and a status.
```elixir
#Helpdesk.Tickets.Ticket<
...
id: "3c94d310-7b5e-41f0-9104-5b193b831a5d",
status: :open,
subject: "My mouse won't click!",
...
>
```
If we didn't include a subject, or left out the input, we would see an error instead
Now lets add some logic to close a ticket. This time we'll add an `update` action.
Here we will use a `change`. Changes allow you to customize how an action executes with very fine-grained control. There are built-in changes that are automatically available as functions, but you can define your own and pass it in as shown below. You can add multiple, and they will be run in order. See the {{link:ash:guide:Actions}} guides for more.
```elixir
actions do
...
update :close do
# We don't want to accept any input here
accept []
change set_attribute(:status, :closed)
# A custom change could be added like so:
#
# change MyCustomChange
# change {MyCustomChange, opt: :val}
end
end
```
Now we can try it out in iex, opening a ticket and closing it:
```elixir
# parenthesis so you can paste into iex
ticket = (
Helpdesk.Tickets.Ticket
|> Ash.Changeset.for_create(:open, %{subject: "My mouse won't click!"})
|> Helpdesk.Tickets.create!()
)
ticket
|> Ash.Changeset.for_update(:close)
|> Helpdesk.Tickets.update!()
#Helpdesk.Tickets.Ticket<
...
status: :closed,
subject: "My mouse won't click!",
...
>
```
### Querying without persistence
So far, there is no persistence happening. All that this simple resource does is return the record back to us. You can see this lack of persistence by attempting to use a `read` action:
```elixir
Helpdesk.Tickets.read!(Helpdesk.Tickets.Ticket)
```
Which will raise an error explaining that there is no data to be read for that resource.
In order to add persistence, we need to add a {{link:ash:guide:Data Layers:Data Layer}} to our resources. Before we do that, however, lets go over how Ash allows us to work against many different data layers (or even no data layer at all). Resources without a data layer will implicitly be using `Ash.DataLayer.Simple`, which will just return structs and do no persistence.
Try the following in iex. We will open some tickets, and close some of them, and then configure the simple data layer to use those tickets
# Show the tickets that are closed and their subject does not contain "4"
Helpdesk.Tickets.Ticket
|> Ash.Query.filter(closed and not(contains(subject, "4")))
|> Ash.DataLayer.Simple.set_data(tickets)
|> Helpdesk.Tickets.read!()
```
The examples shown here could be implemented easily using things like `Enum.filter`, but the real power here is to allow you to use the same tools when working with any data layer. If you were using AshPostgres, the above code would be exactly the same, except for the call to `set_data/2`.
### Adding basic persistence
Before we get into working with relationships, lets add some actual persistence to our resource. This will let us add relationships and try out querying data.
There is a built in data layer that is good for testing and prototyping, that uses [ETS](https://elixir-lang.org/getting-started/mix-otp/ets.html).
To add it to your resource, simply modify it like so:
```elixir
use Ash.Resource,
data_layer: Ash.DataLayer.Ets
```
Now we can slightly modify our code above, by removing the `Ash.DataLayer.Simple.set_data/2` calls, and we can see our persistence in action. Keep in mind, ETS is in memory, meaning restarting your application/iex session will remove all of the data.
Finally, lets add our new resource to our registry
```elixir
# lib/helpdesk/tickets/registry.ex
entries do
...
entry Helpdesk.Tickets.Representative
end
```
You may notice that if you don't add the resource to the registry, or if you don't add the `belongs_to` relationship, that you'll get helpful errors at compile time. Helpful compile time validations are a core concept of Ash. We focus as often as possible on ensuring that your application is valid before it compiles.
## Working with relationships
There are a wide array of options when managing relationships, and going over all of them here wouldn't be reasonable. See the guide on {{link:ash:guide:Managing Relationships}} for a full explanation. For now, we'll show a simple example. Add the following action to allow us to assign a ticket to a representative.
Here we also show the use of action arguments, the method by which you can accept additional input to an action.
```elixir
update :assign do
# No attributes should be accepted
accept []
# We accept a representative's id as input here
argument :representative_id, :uuid do
# This action requires representative_id
allow_nil? false
end
# We use a change here to replace the related representative
# If there is a different representative for this ticket, it will be changed to the new one
# The representative itself is not modified in any way
What you've seen above constitutes some very simple usage of Ash, barely scratching the surface. In a lot of ways, it will look very similar to other tools that you've seen. If all that you ever used was the above, then realistically you won't see much benefit to using Ash over other options. Where Ash shines is in all of the additional turn-key tools that are built in, the ability to extend the framework yourself, and the consistent design patterns that enable unparalleled velocity, power and flexibility as your application and needs grow.
#### Clean up your code that uses Ash?
Creating and using changesets can be verbose. Check out the {{link:ash:guide:Code Interface}} to derive things like `Helpdesk.Tickets.Ticket.assign!(representative.id)`
#### Persist your data
See {{link:ash_postgres:guide:Get Started:AshPostgres}} to see how to back your resources with postgres. This is highly recommended, as the postgres data layer provides tons of advanced capabilities.
See the {{link:ash:guide:Data Layers}} guide on how you might write your own data layer.
#### Add an API
Check out the AshJsonApi and AshGraphql extensions to effortlessly build APIs around your resources
#### Authorize access and work with users
See the {{link:ash:guide:Policies}} guide for information on how to authorize access to your resources using actors and policies.
