# `Soundcheck.Check.Refactor.ExpensiveMountWork`
[🔗](https://github.com/leonqadirie/soundcheck/blob/v0.1.0/lib/soundcheck/check/refactor/expensive_mount_work.ex#L1)

## Basics

> #### This check is disabled by default. {: .neutral}
>
> [Learn how to enable it](`e:credo:config_file.html#checks`) via `.credo.exs`.

This check has a base priority of `normal` and works with any version of Elixir.

## Explanation

Flags database and HTTP calls in a LiveView's `mount/3` outside a
`connected?(socket)` branch. `mount/3` runs twice per page load, once
for the disconnected HTTP render and once when the socket connects, so
the query or request runs twice.

Before:

    def mount(_params, _session, socket) do
      {:ok, assign(socket, :posts, Repo.all(Post))}
    end

After:

    def mount(_params, _session, socket) do
      {:ok, assign_async(socket, :posts, fn -> {:ok, %{posts: Repo.all(Post)}} end)}
    end

Calls inside closures (`assign_async/3`, `start_async/3`) and inside
`if connected?(socket)` do not count. Modules match
`expensive_modules` (atoms or regexes on the alias-expanded name).
Pages that must render the data on the first, disconnected response
(for search engines) load it in both mounts on purpose; leave this
check off for them.

Confidence: medium. Tier: syntactic (works without compiling).

## Check-Specific Parameters

Use the following parameters to configure this check:

### `:excluded_paths`

  Paths to skip (atoms, binaries as path segments, or regexes).

*This parameter defaults to* `[~r/\/test\//, "test"]`.

### `:strict`

  Unused.

*This parameter defaults to* `false`.

### `:expensive_modules`

  Modules whose calls count as expensive: atoms or regexes.

*This parameter defaults to* `[~r/\.Repo$/, ~r/^(Req|Finch|HTTPoison|Tesla)$/]`.

## General Parameters

Like with all checks, [general params](`e:credo:check_params.html`) can be applied.

Parameters can be configured via the [`.credo.exs` config file](`e:credo:config_file.html`).

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