Packages
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3.29.3
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3.27.8
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3.27.5
3.27.4
3.27.3
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3.27.1
3.27.0
3.26.0
3.25.2
3.25.1
3.25.0
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3.24.7
3.24.6
3.24.5
3.24.4
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3.24.1
3.24.0
3.23.1
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3.22.2
3.22.1
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3.21.1
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3.14.1
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3.13.2
3.13.1
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3.6.3
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3.1.8
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3.1.5
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3.1.1
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3.0.1
3.0.0
3.0.0-rc.46
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2.21.15
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2.20.3
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retired
2.19.2
retired
2.19.1
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2.19.0
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2.18.2
2.18.1
2.18.0
2.17.24
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2.17.1
2.17.0
2.16.1
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2.15.20
2.15.19
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2.15.1
2.15.0
2.14.21
2.14.20
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2.14.6
2.14.5
2.14.4
2.14.3
2.14.2
2.14.1
2.14.0
2.13.4
retired
2.13.3
2.13.2
2.13.1
2.13.0
2.12.1
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2.11.11
2.11.10
2.11.9
2.11.8
2.11.7
2.11.6
2.11.5
2.11.4
2.11.3
2.11.2
2.11.1
2.11.0
2.11.0-rc.3
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2.11.0-rc.0
2.10.2
2.10.1
2.10.0
2.9.29
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2.9.27
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2.9.23
2.9.22
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2.9.7
2.9.6
2.9.5
2.9.4
2.9.3
2.9.2
2.9.1
2.9.0
2.8.1
2.8.0
2.7.1
2.7.0
2.6.31
2.6.30
2.6.29
2.6.28
2.6.27
2.6.26
2.6.25
2.6.24
2.6.23
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2.6.13
2.6.11
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2.6.9
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2.6.7
2.6.6
2.6.5
2.6.4
2.6.3
2.6.2
2.6.1
2.6.0
2.5.16
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2.5.11
2.5.10
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1.52.0-rc.22
1.52.0-rc.21
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1.52.0-rc.19
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1.51.2
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1.40.0
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1.36.0
1.35.1
1.35.0
1.34.9
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1.33.0
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1.31.1
1.31.0
1.30.2
1.30.1
1.29.0-rc1
1.29.0-rc0
1.28.1
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1.27.1
1.27.0
1.26.13
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1.25.0
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1.23.3
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1.22.1
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1.20.1
1.20.0
1.19.1
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1.14.0
1.13.4
1.13.3
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1.13.0
1.12.0
1.11.1
1.11.0
1.10.0
1.9.0
1.8.0
1.7.0
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1.6.2
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1.6.0
1.5.1
1.5.0
1.4.1
1.4.0
1.3.1
1.3.0
1.2.1
1.2.0
1.1.3
1.1.2
1.1.0
1.0.3
1.0.2
1.0.1
1.0.0
0.13.1
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0.10.0
0.9.1
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0.3.0
0.2.0
0.1.9
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A declarative, extensible framework for building Elixir applications.
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usage-rules/calculations.md
<!--
SPDX-FileCopyrightText: 2019 ash contributors <https://github.com/ash-project/ash/graphs/contributors>
SPDX-License-Identifier: MIT
-->
# Calculations
Calculations allow you to define derived values based on a resource's attributes or related data. Define calculations in the `calculations` block of a resource:
```elixir
calculations do
# Simple expression calculation
calculate :full_name, :string, expr(first_name <> " " <> last_name)
# Expression with conditions
calculate :status_label, :string, expr(
cond do
status == :active -> "Active"
status == :pending -> "Pending Review"
true -> "Inactive"
end
)
# Using module calculations for more complex logic
calculate :risk_score, :integer, {MyApp.Calculations.RiskScore, min: 0, max: 100}
end
```
## Expression Calculations
Expression calculations use Ash expressions and can be pushed down to the data layer when possible:
```elixir
calculations do
# Simple string concatenation
calculate :full_name, :string, expr(first_name <> " " <> last_name)
# Math operations
calculate :total_with_tax, :decimal, expr(amount * (1 + tax_rate))
# Date manipulation
calculate :days_since_created, :integer, expr(
date_diff(^now(), inserted_at, :day)
)
end
```
## Expressions
In order to use expressions outside of resources, changes, preparations etc. you will need to use `Ash.Expr`.
It provides both `expr/1` and template helpers like `actor/1` and `arg/1`.
For example:
```elixir
import Ash.Expr
Author
|> Ash.Query.aggregate(:count_of_my_favorited_posts, :count, [:posts], query: [
filter: expr(favorited_by(user_id: ^actor(:id)))
])
```
See the expressions guide for more information on what is available in expresisons and
how to use them.
## Module Calculations
For complex calculations, create a module that implements `Ash.Resource.Calculation`:
```elixir
defmodule MyApp.Calculations.FullName do
use Ash.Resource.Calculation
# Validate and transform options
@impl true
def init(opts) do
{:ok, Map.put_new(opts, :separator, " ")}
end
# Specify what data needs to be loaded
@impl true
def load(_query, _opts, _context) do
[:first_name, :last_name]
end
# Implement the calculation logic
@impl true
def calculate(records, opts, _context) do
Enum.map(records, fn record ->
[record.first_name, record.last_name]
|> Enum.reject(&is_nil/1)
|> Enum.join(opts.separator)
end)
end
end
# Usage in a resource
calculations do
calculate :full_name, :string, {MyApp.Calculations.FullName, separator: ", "}
end
```
## Calculations with Arguments
You can define calculations that accept arguments:
```elixir
calculations do
calculate :full_name, :string, expr(first_name <> ^arg(:separator) <> last_name) do
argument :separator, :string do
allow_nil? false
default " "
constraints [allow_empty?: true, trim?: false]
end
end
end
```
## Using Calculations
```elixir
# Using code interface options (preferred)
users = MyDomain.list_users!(load: [full_name: [separator: ", "]])
# Filtering and sorting
users = MyDomain.list_users!(
query: [
filter: [full_name: [separator: " ", value: "John Doe"]],
sort: [full_name: {[separator: " "], :asc}]
]
)
# Manual query building (for complex cases)
User |> Ash.Query.load(full_name: [separator: ", "]) |> Ash.read!()
# Loading on existing records
Ash.load!(users, :full_name)
```
### Code Interface for Calculations
Define calculation functions on your domain for standalone use:
```elixir
# In your domain
resource User do
define_calculation :full_name, args: [:first_name, :last_name, {:optional, :separator}]
end
# Then call it directly
MyDomain.full_name("John", "Doe", ", ") # Returns "John, Doe"
```