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97 lines
3.1 KiB
Markdown
97 lines
3.1 KiB
Markdown
# Calculations
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Calculations in Ash allow for displaying complex values as a top level value of a resource.
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## Declaring calculations on a resource
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### Expression Calculations
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The simplest kind of calculation refers to an Ash expression. For example:
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```elixir
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calculations do
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calculate :full_name, :string, expr(first_name <> " " <> last_name)
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end
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```
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See the [Expressions guide](/documentation/topics/expressions.md) for more.
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### Module Calculations
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When calculations require more complex code or can't be pushed down into the data layer, a module that uses `Ash.Calculation` can be used.
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```elixir
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defmodule Concat do
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# An example concatenation calculation, that accepts the delimiter as an argument,
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#and the fields to concatenate as options
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use Ash.Calculation
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# Optional callback that verifies the passed in options (and optionally transforms them)
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@impl true
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def init(opts) do
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if opts[:keys] && is_list(opts[:keys]) && Enum.all?(opts[:keys], &is_atom/1) do
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{:ok, opts}
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else
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{:error, "Expected a `keys` option for which keys to concat"}
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end
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end
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@impl true
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def calculate(records, opts, %{separator: separator}) do
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Enum.map(records, fn record ->
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Enum.map_join(opts[:keys], separator, fn key ->
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to_string(Map.get(record, key))
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end)
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end)
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end
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# You can implement this callback to make this calculation possible in the data layer
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# *and* in elixir. Ash expressions are already executable in Elixir or in the data layer, but this gives you fine grain control over how it is done
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# @impl true
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# def expression(opts, context) do
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# end
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end
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# Usage in a resource
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calculations do
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calculate :full_name, :string, {Concat, keys: [:first_name, :last_name]} do
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# You currently need to use the [allow_empty?: true, trim?: false] constraints here.
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# The separator could be an empty string or require a leading or trailing space,
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# but would be trimmed or even set to `nil` without the constraints.
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argument :separator, :string, constraints: [allow_empty?: true, trim?: false]
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end
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end
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```
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See the documentation for the calculations section in `Ash.Resource.Dsl` and the `Ash.Calculation` docs for more information.
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The calculations declared on a resource allow for declaring a set of named calculations that can be used by extensions.
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They can also be loaded in the query using `Ash.Query.load/2`, or after the fact using `c:Ash.Api.load/3`. Calculations declared on the resource will be keys in the resource's struct.
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## Custom calculations in the query
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Example:
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```elixir
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User
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|> Ash.Query.new()
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|> Ash.Query.calculate(:full_name, {Concat, keys: [:first_name, :last_name]}, :string, %{separator: ","})
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```
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See the documentation for `Ash.Query.calculate/4` for more information.
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## Arguments in calculations
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Using the above example with arguments, you can load a calculation with arguments like so:
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```elixir
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load(full_name: [separator: ","])
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```
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If the calculation uses an expression, you can also filter and sort on it like so:
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```elixir
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query
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|> Ash.Query.filter(full_name(separator: ","))
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|> Ash.Query.sort(full_name: {:asc, %{separator: ","}})
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```
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