Problem with foreign key insertion in Postgres bank - Elixir / Phoenix

I'm new to using Elixir and would like to do a foreign key insertion in the bank (Postgres) via POST (it's a JSON)

below my modules

defmodule MeuProjeto.Carteiras.Carteira do
  use Ecto.Schema
  import Ecto.Changeset


  schema "carteiras" do
    field :campo_1, :string
    field :campo_2, :integer
    field :moedas_id, :id
    has_one :moeda, MeuProjeto.Moedas.Moeda

    timestamps()
  end

  @doc false
  def changeset(carteira, attrs) do
    carteira
    |> cast(attrs, [:campo_1, :campo_2])
    |> validate_required([:campo_1, :campo_2])
  end
end

and

defmodule MeuProjeto.Moedas.Moeda do
  use Ecto.Schema
  import Ecto.Changeset


  schema "moedas" do
    field :nome, :string
    belongs_to :carteira, MeuProjeto.Carteiras.Carteira

    timestamps()
  end

  @doc false
  def changeset(moeda, attrs) do
    moeda
    |> cast(attrs, [:nome])
    |> validate_required([:nome])
  end
end

In the database, the relationship already exists, currency_id is a foreign key in the "wallets" table.

When I do POST, it returns this error, showing the entire struct with the fields, and with the primary key missing message:

  

struct %MeuProjeto.Carteiras.Carteira{...} is missing primary key value

I still can not figure out how to put this primary key, I found that only using has_one and belongs_to it already made the association. I've also put in the validate_required field with the foreign key, but I read that this could generate security holes, and the error remained the same.

EDIT Ok, after searching I understood what the problem was.

First that I do not need this has_one / belongs_to relationship if I will not use the data from my table that the foreign key directs.

And after that I was missing the foreign_key_constraint () function in my Wallet schema.

The final code was thus:

defmodule MeuProjeto.Carteiras.Carteira do
  use Ecto.Schema
  import Ecto.Changeset


  schema "carteiras" do
    field :campo_1, :string
    field :campo_2, :integer
    field :moedas_id, :id

    timestamps()
  end

  @doc false
  def changeset(carteira, attrs) do
    carteira
    |> cast(attrs, [:campo_1, :campo_2, :moedas_id])
    |> foreign_key_constraint(:moedas_id)
    |> validate_required([:campo_1, :campo_2, :moedas_id])
  end
end

In the Currency schema, I just removed the has_one: currency, MyProject.Moedas.Moeda