Bylaw.Credo.Check.Ecto.PreferRepoOneOverAllFirst (bylaw_credo v0.3.1)

Basics

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

Explanation

Prefer a single-row Repo read over loading every matching row and taking the first result in Elixir.

Examples

Avoid:

query
|> Repo.all()
|> List.first()

query
|> Repo.all()
|> Enum.at(0)

query
|> Repo.all()
|> hd()

When the query is expected to return zero or one row, prefer:

Repo.one(query)

When the query intentionally selects the first row from an ordered result, preserve that intent in the query:

query
|> Ecto.Query.first()
|> Repo.one()

Use the bang variants when a missing row is exceptional. For primary-key lookups, prefer Repo.get/2 or Repo.get!/2.

Notes

This check uses static AST analysis. It reports direct Repo.all and first-element selection with List.first/1, Enum.at/2 with the literal index 0, or hd/1, including piped forms. It cannot infer whether the caller expects uniqueness or an ordered first row. Other Enum.at/2 indices are outside this check's scope because they express different offset and ordering semantics.

Options

This check has no check-specific options. Configure it with an empty option list.

Usage

Add this check to Credo's checks: list in .credo.exs:

%{
  configs: [
    %{
      name: "default",
      checks: [
        {Bylaw.Credo.Check.Ecto.PreferRepoOneOverAllFirst, []}
      ]
    }
  ]
}

Check-Specific Parameters

There are no specific parameters for this check.

General Parameters

Like with all checks, general params can be applied.

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