小编Joh*_*n P的帖子

通过示例指南工作。本章中详细介绍的内容在我的应用程序中不起作用。看起来很简单的东西。我有一个视频模型：

defmodule Rumbl.Video do
  use Rumbl.Web, :model

  schema "videos" do
    field :url, :string
    field :title, :string
    field :description, :string
    belongs_to :user, Rumbl.User
    belongs_to :category, Rumbl.Category

    timestamps()
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, [:url, :title, :description])
    |> validate_required([:url, :title])
    |> assoc_constraint(:category)
  end
end

我还有一个类别模型：

defmodule Rumbl.Category do
  use Rumbl.Web, :model

  schema "categories" do
    field :name, :string

    timestamps()
  end

  @doc """
  Builds a changeset based on …