Ecto 查询以子项为条件获取孙子项

Question

获取特定 user 的 posts 的所有 comments 的最佳方法是什么，其中 post 是在特定日期发布的？

即some_user.posts.comments where post.published_on == '2016-01-01'

我对作为中间步骤获取帖子不感兴趣，只对评论感兴趣。

Answer 1

您需要 join 和 assoc(post, :comments) 然后 select 只有评论：

from(p in Post,
  where: p.user_id == ^user.id and p.inserted_at == ^"2016-10-12T08:30:34Z",
  join: c in assoc(p, :comments),
  select: c)

iex(1)> user = Repo.get!(User, 1)
iex(2)> Repo.all from(p in Post, where: p.user_id == ^user.id and p.inserted_at == ^"2016-10-12T08:30:34Z", join: c in assoc(p, :comments), select: c)
[debug] QUERY OK source="posts" db=0.6ms
SELECT c1."id", c1."content", c1."post_id", c1."user_id", c1."inserted_at", c1."updated_at" FROM "posts" AS p0 INNER JOIN "comments" AS c1 ON c1."post_id" = p0."id" WHERE ((p0."user_id" = ) AND (p0."inserted_at" = )) [1, {{2016, 10, 12}, {8, 30, 34, 0}}]

[%MyApp.Comment{__meta__: #Ecto.Schema.Metadata<:loaded, "comments">,
  content: nil, id: 1, inserted_at: #Ecto.DateTime<2016-10-12 08:30:42>,
  post: #Ecto.Association.NotLoaded<association :post is not loaded>,
  post_id: 1, updated_at: #Ecto.DateTime<2016-10-12 08:30:42>,
  user: #Ecto.Association.NotLoaded<association :user is not loaded>,
  user_id: 1},
 %MyApp.Comment{__meta__: #Ecto.Schema.Metadata<:loaded, "comments">,
  content: nil, id: 2, inserted_at: #Ecto.DateTime<2016-10-12 08:39:41>,
  post: #Ecto.Association.NotLoaded<association :post is not loaded>,
  post_id: 1, updated_at: #Ecto.DateTime<2016-10-12 08:39:41>,
  user: #Ecto.Association.NotLoaded<association :user is not loaded>,
  user_id: 1},
 %MyApp.Comment{__meta__: #Ecto.Schema.Metadata<:loaded, "comments">,
  content: nil, id: 3, inserted_at: #Ecto.DateTime<2016-10-12 08:39:42>,
  post: #Ecto.Association.NotLoaded<association :post is not loaded>,
  post_id: 1, updated_at: #Ecto.DateTime<2016-10-12 08:39:42>,
  user: #Ecto.Association.NotLoaded<association :user is not loaded>,
  user_id: 1}]

我上面的应用程序没有 published_on : Ecto.Date，所以我使用了 inserted_at : Ecto.DateTime。只需将 inserted_at 更改为 published_on 并将值更改为可以由 ecto 转换为 Ecto.Date 的有效类型，它应该适用于您的应用程序。

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