# Aggregates

Aggregates allow you to retrieve summary information over groups of related data, like counts, sums, or averages. Define aggregates in the `aggregates` block of a resource.

Aggregates can work over relationships or directly over unrelated resources:

```elixir
aggregates do
  # Related aggregates - use relationship path
  count :published_post_count, :posts do
    filter expr(published == true)
  end

  sum :total_sales, :orders, :amount

  exists :is_admin, :roles do
    filter expr(name == "admin")
  end

  # Unrelated aggregates - use resource module directly
  count :matching_profiles_count, Profile do
    filter expr(name == parent(name))
  end
  
  sum :total_report_score, Report, :score do
    filter expr(author_name == parent(name))
  end
  
  exists :has_reports, Report do
    filter expr(author_name == parent(name))
  end
end
```

For unrelated aggregates, use `parent/1` to reference fields from the source resource.

## Aggregate Types

- **count**: Counts related items meeting criteria
- **sum**: Sums a field across related items
- **exists**: Returns boolean indicating if matching related items exist (also supports unrelated resources)
- **first**: Gets the first related value matching criteria
- **list**: Lists the related values for a specific field
- **max**: Gets the maximum value of a field
- **min**: Gets the minimum value of a field
- **avg**: Gets the average value of a field

## Using Aggregates

```elixir
# Using code interface options (preferred)
users = MyDomain.list_users!(
  load: [:published_post_count, :total_sales],
  query: [
    filter: [published_post_count: [greater_than: 5]],
    sort: [published_post_count: :desc]
  ]
)

# Manual query building (for complex cases)
User |> Ash.Query.filter(published_post_count > 5) |> Ash.read!()

# Loading on existing records
Ash.load!(users, :published_post_count)
```

### Join Filters

For complex aggregates involving multiple relationships, use join filters:

```elixir
aggregates do
  sum :redeemed_deal_amount, [:redeems, :deal], :amount do
    # Filter on the aggregate as a whole
    filter expr(redeems.redeemed == true)

    # Apply filters to specific relationship steps
    join_filter :redeems, expr(redeemed == true)
    join_filter [:redeems, :deal], expr(active == parent(require_active))
  end
end
```

## Inline Aggregates

Use aggregates inline within expressions:

```elixir
# Related inline aggregates
calculate :grade_percentage, :decimal, expr(
  count(answers, query: [filter: expr(correct == true)]) * 100 /
  count(answers)
)

# Unrelated inline aggregates
calculate :profile_count, :integer, expr(
  count(Profile, filter: expr(name == parent(name)))
)

calculate :stats, :map, expr(%{
  profiles: count(Profile, filter: expr(active == true)),
  reports: count(Report, filter: expr(author_name == parent(name))),
  has_active_profile: exists(Profile, active == true and name == parent(name))
})
```