Post param parsed as integer

So I have my form with those fields POSTed:

utf8: ✓
_csrf_token: a1ILBA0eGSJSJggHJ25GYj8IIEACShkC8bgoudFN8DcUCC01EIT2Mxjl
_method: put
certification[id]: 10
certification[is_active]: true
certification[rncp_id]: 367
certification[acronym]: Diplôme
certification[level]: 7
commit: Update Certification

But on the server side, once the params are parsed, I get the following map:

%{
  id: 10,
  is_active: true,
  rncp_id: 367,
  acronym: "Diplôme",
  level: "7"
}

:id is an integer so I’m happy it was parsed, but neither :rncp_id nor :level are. Why does :rncp_id gets parsed as integer while :level correctly won’t?

I’m guessing this is because its name finishes with _id, but could this any how make sense here?

This breaks my changeset afterwards, with some: errors: [rncp_id: {"is invalid", [type: :string, validation: :cast]}] error.

Why is this happening? Why such subjective rule if so? Anyway the fields are casted afterwards so it wouldn’t matter to keep it as a string.

Anyway, I’ll go for a dirty:

    params = case params[:rncp_id] do
      v when is_integer(v) -> Map.put(params, :rncp_id, Integer.to_string(v))
      _ -> params
    end

for now.

Thanks