[Proposal] For `Repo.reload` functions, add support for items with multiple primary keys

[Nicholas Moen]

Problem: The functions `Repo.reload/2` (and its associated bang function) do not support reloading items with multiple primary keys.

Current solution: Here are the helper functions I have created to accomplish this in some of my tests:

```elixir

defmodule MyProject.TestHelpers.Ecto.Repo do
  @moduledoc "`Ecto.Repo` test helpers."

  alias MyProject.Repo

  @doc "Similar to `Repo.reload/2`, but supports structs with multiple primary keys."
  def reload(%_{} = struct, opts \\ []) do
    case struct.__struct__.__schema__(:primary_key) do
      [_pk] ->
        Repo.reload(struct, opts)

      _pks ->
        get_by_clauses =
          struct.__struct__.__schema__(:primary_key)
          |> Keyword.new(fn primary_key_field ->
            {primary_key_field, Map.fetch!(struct, primary_key_field)}
          end)

        Repo.get_by(struct.__struct__, get_by_clauses, opts)
    end
  end

  @doc "Similar to `Repo.reload!/2`, but supports structs with multiple primary keys."
  def reload!(%_{} = struct, opts \\ []) do
    case struct.__struct__.__schema__(:primary_key) do
      [_pk] ->
        Repo.reload!(struct, opts)

      _pks ->
        get_by_clauses =
          struct.__struct__.__schema__(:primary_key)
          |> Keyword.new(fn primary_key_field ->
            {primary_key_field, Map.fetch!(struct, primary_key_field)}
          end)

        Repo.get_by!(struct.__struct__, get_by_clauses, opts)
    end
  end
end

```

Proposal: Is there any interest in integrating this functionality into Ecto?

I realize that I would have to modify the functions to use the abstractions used by the existing Repo.reload functions. I just wanted to reach out before doing any work in case the omission of this functionality is intentional.

Thanks

[José Valim]

I think the issue is reloading multiple records, because then you need to align the pairs (or write very verbose queries). Or perhaps there is a way we can work around that?

José Valim

https://dashbit.co/

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[Greg Rychlewski]

The best solution i can think of is to join on values lis.