与条件的ecto关联 [英] Ecto association with a condition

问题描述

假设我有两个模型，分别是Post和Comment，注释模型可以是normal和fancy这两种类型中的一种，由comments列中的type定义.桌子.

现在我想在我的Post模型上添加2个关联，其中1个引用花哨的注释，而1个引用普通的注释，我该怎么做?所以我想要这样的东西:

has_many :fancy_comments, MyApp.Comment, where: [type: 0]
has_many :normal_comments, MyApp.Comment, where: [type: 1]

解决方案

在ecto中不可用，在可组合查询的博客文章.

您还可以在查询中使用预加载:

fancy_query = from(c in Comments, where: type == 0)
Repo.preload(post, comments: fancy_query)

Let's say I have two models, Post and Comment and the comment model can be 1 out of 2 types, normal and fancy which is defined by the column type in the comments table.

Now I want to add 2 associations on my Post model, where one refers to fancy comments and one to normal ones, how would I do it? So I want something like this:

has_many :fancy_comments, MyApp.Comment, where: [type: 0]
has_many :normal_comments, MyApp.Comment, where: [type: 1]

解决方案

This is not available in Ecto, there is a lengthy discussion about it on this GitHub issue.

You could use a composable query for this:

defmodule MyApp.Comment do

  ...schema, etc.

  def fancy(query) do
    from c in query,
      where: type == 0
  end

  def normal(query) do
    from c in query,
      where: type == 1
  end    
end

You can then use has_many :comments, MyApp.Comment and query based on that:

assoc(post, :comments) |> Comment.fancy() |> Repo.all()

Here is a blog post about composable queries.

You can also use a preload with a query:

fancy_query = from(c in Comments, where: type == 0)
Repo.preload(post, comments: fancy_query)

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