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# Ash: 8 - Aggregates
```elixir
Application.put_env(:ash, :validate_domain_resource_inclusion?, false)
Application.put_env(:ash, :validate_domain_config_inclusion?, false)
Mix.install([{:ash, "~> 3.0"}], consolidate_protocols: false)
```
## Aggregates
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### In this tutorial you will add an Aggregate on a Resource
[Aggregates](https://hexdocs.pm/ash/aggregates.html) in Ash allow for retrieving summary information over groups of related data. Aggregates can be either _count_, _first_, _sum_ or _list_.
Implement a count aggregate on the 'open tickets' a representative is assigned to.
First explore the comments in the code below, to make this work properly you have to add the inverse relationship of belongs_to inside the Representative resource.
To add an aggregate define an `aggregates do .. end` block inside the representative.
Inside the `aggregates` block, define a `count :count_of_open_tickets, :tickets do .. end` block.
Then inside this block, define a filter like so: `filter expr(status == :open)`
Also, notice what happens when you don't define a filter.
<details class="rounded-lg my-4" style="background-color: #96ef86; color: #040604;">
<summary class="cursor-pointer font-bold p-4"></i>Show Solution</summary>
<div class="p-4">
```elixir
aggregates do
count :count_of_open_tickets, :tickets do
filter expr(status == :open)
end
end
```
</div>
</details>
### Enter your solution
```elixir
defmodule Tutorial.Support.Ticket do
use Ash.Resource,
domain: Tutorial.Support,
data_layer: Ash.DataLayer.Ets
actions do
defaults [:read]
# On creation set the representative by providing the id
create :open do
accept [:subject, :description, :representative_id]
end
update :close do
accept []
change set_attribute(:status, :closed)
end
update :assign do
accept [:representative_id]
end
end
attributes do
uuid_primary_key(:id)
attribute :subject, :string, allow_nil?: false
attribute :description, :string, allow_nil?: true
attribute :status, :atom do
constraints one_of: [:open, :closed]
default :open
allow_nil? false
end
create_timestamp :created_at
update_timestamp :updated_at
end
relationships do
belongs_to :representative, Tutorial.Support.Representative
end
code_interface do
define :assign, args: [:representative_id]
# <- added representative_id
define :open, args: [:subject, :description, :representative_id]
define :close, args: []
end
end
defmodule Tutorial.Support.Representative do
use Ash.Resource,
domain: Tutorial.Support,
data_layer: Ash.DataLayer.Ets
actions do
defaults [:read]
create :create do
accept [:name]
end
end
attributes do
uuid_primary_key :id
attribute :name, :string
end
# Added the inverse relationship of belongs_to in the ticket.
# This way we can reference :tickets inside the aggregates.
relationships do
has_many :tickets, Tutorial.Support.Ticket
end
code_interface do
define :create, args: [:name]
end
# <- Add the aggregates here
end
```
```elixir
defmodule Tutorial.Support do
use Ash.Domain
resources do
resource Tutorial.Support.Ticket
resource Tutorial.Support.Representative
end
end
```
## Query the Aggregate
Use a [Bulk Create](https://hexdocs.pm/ash/create-actions.html#bulk-creates) to create 4 tickets, 3 of which are assigned to Joe.
```elixir
# Create a representative
joe = Tutorial.Support.Representative.create!("Joe Armstrong")
# Bulk create 4 tickets, 3 of which are assigned to Joe
[
%{subject: "I can't see my eyes!"},
%{subject: "I can't find my hand!", representative_id: joe.id},
%{subject: "My fridge is flying away!", representative_id: joe.id},
%{subject: "My bed is invisible!", representative_id: joe.id}
]
|> Ash.bulk_create(Tutorial.Support.Ticket, :open, return_records?: true)
```
Close the last ticket assigned to Joe.
```elixir
require Ash.Query
# Retrieve the last ticket
[last_ticket] =
Tutorial.Support.Ticket
|> Ash.Query.filter(representative_id == ^joe.id)
|> Ash.Query.sort(created_at: :desc)
|> Ash.Query.limit(1)
|> Ash.read!()
# Close the last ticket
Tutorial.Support.Ticket.close!(last_ticket)
```
```elixir
joe = Ash.load!(joe, [:count_of_open_tickets])
joe.count_of_open_tickets
```
The result should be __2__, as you opened 4 tickets, 3 were assigned to Joe, but the last assigned ticket was closed.
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