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62 lines
2.2 KiB
Markdown
62 lines
2.2 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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They are relatively limited in their current form, supporting only functional calculations,
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where you provide a module that takes a list of records and returns a list of values for that
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calculation. Eventually, there will be support for calculations that can be embedded into the
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data layer(for things like postgres) that will allow for sorting and filtering on calculated
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data.
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## Declaring calculations on a resource
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Example:
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```elixir
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defmodule Concat do
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# An example concatenation calculation, that accepts the delimeter as an argument, and the fields to concatenate as options
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use Ash.Calculation, type: :string
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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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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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end
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# Usage in a resource
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calculations do
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calculate :full_name, {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` 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]}, %{separator: ","})
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```
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See the documentation for `Ash.Query.calculate/4` for more information.
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