Get all posts of categories with just subcategories relations from GraphQL request

Question

Have a simple model like post / category / subcategory with relation between posts <-> subcategories & categories <-> subcategories.

Questions are :

• How to make the GraphQL request with the gatsby-source-contentful plugin in order to get all post in category page (without adding a relation field between posts & categories ?
• Is it the Contentful right way for having post classification in a 2 levels tree ?

Seems to be enable by Contentful API as said in this post : https://www.contentful.com/blog/2015/02/17/content-trees-tags-and-facets-in-contentful/

Thx for replies

{
  contentfulCategory(id: {eq: $id}) {
    id
    title
    post <- ?
    subcategories {
        slug
        title
        post {
            id
            title
        }
    }
  }
}

Maybe a way to do that is something close to :

{
  contentfulCategory(id: {eq: $id}) {
    id
    title
    subcategories {
        slug
        title
    }
  }
  allContentfulPost(filter to category ?) {
   edges {
    node {
     slug
     title
    }
  }
}