Api.get!(Blog, 80)
|> Api.load(users: [posts: Ash.Query.filter(blog_id == ^80)])

There is not really a good way to accomplish this if I’m being honest. It’s not a pattern that would be easily generalizable to support all of the relationship features that Ash has. You’d potentially be able to accomplish this with a calculation on the parent object (blog) that produces a list of users and for each their posts in the parent blog. I.e

defmodule YourApp.Types.UserWithPosts do
  use Ash.Resource, data_layer: :embedded

  attributes do
    attribute :user, :struct do
      constraints [instance_of: User]
      allow_nil? false
    end

    attribute :posts, {:array, :struct} do
      constraints [items: [instance_of: Post]]
      allow_nil? false
    end
  end 
end

# in blog
calculate :users_and_posts, {:array, YourApp.Types.UserWithPosts}, YourCalculation

Where YourCalculation is a module that produces a list of those embedded types.