I have a Phoenix app which is using ecto/postgres. I have setup two schemas (User has many Groups) and a seed file (contents below). I am running into an error when I add the group (which is supposed to have a user). I feel like the user association, where the constraint goes (requiring user_id vs assoc_constraint(:user)) and then how the seeding flows I am confused on.

Error I am getting

** (Ecto.InvalidChangesetError) could not perform insert because changeset is invalid.

Errors

    %{user_id: [{"can't be blank", [validation: :required]}]}

Applied changes

    %{description: "Random text", name: "Family"}

Params

    %{
      "description" => "Random text",
      "name" => "Family",
      "user" => %XXXX.Accounts.User{
        __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
        email: "example@gmail.com",
        groups: #Ecto.Association.NotLoaded<association :groups is not loaded>,
        id: 1,
        inserted_at: ~N[2020-05-19 22:43:11],
        name: "Example User",
        password: "secret",
        password_hash: "XXXXXXXX",
        phonenumber: "1 203-247-7113",
        updated_at: ~N[2020-05-19 22:43:11],
        username: "exampleuser"
      }
    }

Changeset

    #Ecto.Changeset<
      action: :insert,
      changes: %{description: "Random text", name: "Family"},
      errors: [user_id: {"can't be blank", [validation: :required]}],
      data: #XXXX.People.Group<>,
      valid?: false

User Schema

defmodule XXXX.Accounts.User do
  use Ecto.Schema
  import Ecto.Changeset

  schema "users" do
    field :email, :string
    field :name, :string
    field :password_hash, :string
    field :password, :string, virtual: true
    field :phonenumber, :string
    field :username, :string

    has_many :groups, XXXX.People.Group

    timestamps()
  end

  def changeset(user, attrs) do
    user
    |> cast(attrs, [:name, :username, :email, :password, :phonenumber])
    |> validate_required([:name, :username, :email, :password, :phonenumber])
    |> validate_length(:username, min: 4)
    |> validate_length(:password, min: 4)
    |> unique_constraint(:username)
    |> unique_constraint(:email)
    |> unique_constraint(:phonenumber)
    |> hash_password()
  end

  defp hash_password(changeset) do
    case changeset do
      %Ecto.Changeset{valid?: true, changes: %{password: password}} ->
        put_change(changeset, :password_hash, Pbkdf2.hash_pwd_salt(password))
      _ ->
        changeset
    end
  end
end

User Migration

defmodule XXXX.Repo.Migrations.CreateUsers do
  use Ecto.Migration

  def change do
    create table(:users) do
      add :name, :string, null: false
      add :username, :string, null: false
      add :email, :string, null: false
      add :password_hash, :string, null: false
      add :phonenumber, :string, null: false

      timestamps()
    end

    create unique_index(:users, [:username, :email, :phonenumber])
  end
end

Group Schema

defmodule XXXX.People.Group do
  use Ecto.Schema
  import Ecto.Changeset

  schema "groups" do
    field :description, :string
    field :name, :string

    belongs_to :user, XXXX.Accounts.User

    timestamps()
  end

  def changeset(group, attrs) do
    required_fields = [:name, :user_id]
    optional_fields = [:description]

    group
    |> cast(attrs, required_fields ++ optional_fields)
    |> validate_required(required_fields)
    |> assoc_constraint(:user)
  end
end

Group Migration

defmodule XXXX.Repo.Migrations.CreateGroups do
  use Ecto.Migration

  def change do
    create table(:groups) do
      add :name, :string, null: false
      add :description, :text
      add :user_id, references(:users, on_delete: :delete_all), null: false

      timestamps()
    end

  end
end

seeds.exs

alias XXXX.Repo
alias XXXX.People.Group
alias XXXX.Accounts.User


user_example_1 = %User{} |> User.changeset(%{
  name: "Example User",
  username: "exampleuser",
  phonenumber: "1 834-000-0000",
  email: "example@gmail.com",
  password: "secret"
}) |> Repo.insert!

example_group1 = %Group{} |> Group.changeset(%{
  name: "Family",
  description: "Random text",
  user: user_example_1
}) |> Repo.insert!