[Proposal] Support lists in clauses of Repo.all_by

[Emmanouil Emmanouilidis]

It would be nice as a convenience to be able to do

```elixir

Repo.all_by(Person, email: ["a...@foo.com", "d...@bar.com"])

```

Today the value of each clause is literally compared with a `==`, resulting in messages like

```elixir

iex> Repo.all_by(Person, email: ["a...@foo.com", "d...@bar.com"])

** (Ecto.Query.CastError) deps/ecto/lib/ecto/repo/queryable.ex:25: value `["a...@foo.com", "d...@bar.com"]` in `where` cannot be cast to type :string in query:

from p0 in MyApp.Person,
  prefix: "public",
  where: po.id == ^["a...@foo.com", "d...@bar.com"],
  select: p0

``` 

It would be nice instead if a list was given to generate an `x in [...]` query.

Caveat: this might break usages where the field type is actually an `{:array, ...}` and the user did intent to compare with `==`.

Thanks for reading,
Manos

[José Valim]

The syntax here is explicit by design to avoid ambiguity and surprising security issues. For example, if you do:

    Repo.all_by(email: ^params[:email])

You may have intended a single email but now anyone can pass a list and you have to guarantee your code will work and be safe with both assumptions.

This is why null checks, memberships, and equality are all distinct operators in Ecto.

José Valim

https://dashbit.co/

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[Emmanouil Emmanouilidis]

Ah, I see, thanks for expanding on where you're coming from. Would including an option like `list_semantics: :equals / :in` (the default being `:equals` so that existing clients don't break), e.g. `Repo.all_by(Person, email: ["a...@foo.com", "d...@bar.com"], list_semantics: :in)` be any better? If I decided to try my hand in this, would it be something interesting for Ecto in general?

[José Valim]

Then you should use the regular query syntax that supports all of those things. We don’t plan to incorporate said options into Ecto!

José Valim

https://dashbit.co/

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