小编Eri*_*kas的帖子

在Rails中,如果我有以下设置:

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post

  def self.approved
    where(approved: true)
  end
end

然后我可以做这样的事情:

post = Post.find(100)
comments = post.comments.approved

快速获得给定的所有批准的评论Post.

我怎样才能在Ecto中做类似的事情？

defmodule MyApp.Post do
  use Ecto.Model

  schema "posts" do
    #columns omitted
    has_many :comments, MyApp.Comment
  end
end

defmodule MyApp.Comment do
  use Ecto.Model

  schema "comments" do
    #columns omitted
    belongs_to :post, MyApp.Post
  end
end

我post有comments预装的:

post = MyApp.Post
       |> MyApp.Repo.get(100)
       |> MyApp.Repo.preload(:comments)

我甚至不确定从哪个approved范围开始MyApp.Comment.