OeditusCredo.Check.Warning.NPlusOneQuery (OeditusCredo v0.6.2)

Basics

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

Explanation

N+1 query antipattern occurs when iterating over collections and querying the database for each item.

This leads to poor performance. Use Ecto's preload/2 to fetch associations in a single query.

Bad:

users = Repo.all(User)
Enum.map(users, fn user ->
  posts = Repo.get_by(Post, user_id: user.id)
  {user, posts}
end)

Good:

import Ecto.Query
users = User |> preload(:posts) |> Repo.all()
Enum.map(users, fn user -> {user, user.posts} end)

Check-Specific Parameters

Use the following parameters to configure this check:

:exclude_test_files

Set to true to skip test files (default: false)

This parameter defaults to nil.

General Parameters

Like with all checks, general params can be applied.

Parameters can be configured via the .credo.exs config file.