# `Arc.ReadModel`
[🔗](https://github.com/Cratis/Arc.Elixir/blob/main/lib/arc/read_model.ex#L4)

A read model container: the module that declares queries over one model type.

The `model` is any struct, typically a Chronicle read model. Arc infers the TypeScript shape
from its fields, so the model stays a plain Chronicle read model.

    defmodule MyApp.Authors.Listing.Authors do
      @moduledoc "Queries over authors."
      use Arc.ReadModel, model: MyApp.Authors.Author

      @query many: true
      def all_authors(_args, _ctx), do: Chronicle.all(MyApp.Authors.Author)

      @query params: [id: :uuid], many: false
      def by_id(%{id: id}, _ctx), do: Chronicle.read_model(MyApp.Authors.Author, id)

      @observe many: true, watch: [MyApp.Authors.Author]
      def live_authors(_args, _ctx), do: Chronicle.all(MyApp.Authors.Author)
    end

Each annotated function takes `(args, ctx)` where `args` is a map of the declared, converted
parameters, and returns `{:ok, value}` or `{:error, results}`.

## Options of `use Arc.ReadModel`

  * `:model` - (required) the struct the queries return
  * `:types` - overrides for inferred field types in the generated proxy, for example
    `types: [id: :uuid]`. Arc infers a type from each struct default; a `nil` or `""` default is a string.

## `@query` / `@observe` options

  * `:params` - keyword list of `name: type`, or `name: {type, optional: true}`
  * `:many` - the query returns a list (default `true`); Arc applies `page`, `pageSize`,
    `sortBy` and `sortDirection` to lists unless the function returns an `Arc.Page`
  * `:authorize` / `:allow_anonymous` - override the module-level declaration
  * `:http_method` - `:get` or `:query` to prefer one in the generated client

`@observe` additionally takes:

  * `:watch` - Chronicle read model modules; the query re-runs when any of them changes
  * `:topics` - `Arc.Notifier` topics that re-run the query when notified

# `allow_anonymous`
*macro* 

Allows anonymous callers for every query of the module.

# `authorize`
*macro* 

Declares who may run every query of the module. See `Arc.Authorization`.

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*Consult [api-reference.md](api-reference.md) for complete listing*