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reach lib reach plugins ecto smells repo_call_in_loop.ex
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lib/reach/plugins/ecto/smells/repo_call_in_loop.ex 

defmodule Reach.Plugins.Ecto.Smells.RepoCallInLoop do

  @moduledoc "Detects Repo calls inside enumerable loops that can cause N+1 queries."



  @behaviour Reach.Smell.Check



  alias Reach.IR

  alias Reach.Smell.Finding

  alias Reach.Smell.Helpers



  @enum_loop_fns [:map, :each, :flat_map, :filter, :reduce, :reject]

  @repo_modules [Repo, Ecto.Repo]



  @impl true

  def kinds, do: [:ecto_repo_call_in_loop]



  @impl true

  def run(project) do

    project.nodes

    |> Enum.flat_map(fn

      {_id, %{type: :call, meta: %{module: Enum, function: fun}} = call}

      when fun in @enum_loop_fns ->

        findings_for_enum_call(call)



      _entry ->

        []

    end)

  end



  defp findings_for_enum_call(call) do

    call.children

    |> Enum.filter(&(&1.type == :fn))

    |> Enum.flat_map(&repo_calls/1)

    |> Enum.map(fn repo_call ->

      Finding.new(

        kind: :ecto_repo_call_in_loop,

        message: "Repo call inside Enum callback may cause N+1 queries; batch or preload instead",

        location: Helpers.location(repo_call)

      )

    end)

  end



  defp repo_calls(fn_node) do

    fn_node

    |> IR.all_nodes()

    |> Enum.filter(&repo_call?/1)

  end



  defp repo_call?(%{type: :call, meta: %{module: module}}) when module in @repo_modules, do: true

  defp repo_call?(_node), do: false

end