Ecto Preload with Condition from the Main Query

Hi guys just wondering is it possible to preload but with a condition from the main query

Let’s say I have a model named Post. A Post has a tag which is a string. Then I want to query a specific Post for example Post with id = idA. While querying the Post I also want to preload all other Post which have a similar tag under a field called similar_posts in the query. So it looks something like this:

 %Post{
      id: "ID_A",
      tag: "TopicA",
      similar_posts: [
        %Post{
          id: "ID_B",
          tag: "topicA"
        },
        %Post{
          id: "ID_C",
          tag: "TopicA"
        }
      ]
    }

Let’s say I already created an association in the Post model:

has_many :similar_posts, MyApp.Post

When I tried

from(p in Post,
    preload: [similar_posts: ^from(pp in Post, 
         where: pp.id != p.id and
                pp.tag == p.tag, 
         order_by: pp.inserted_at
    )]
)

It error said that p is undefined. Can someone help me? Am I doing something wrong here or is it not possible and better to seperate the query itself after retrieving the result.