Ecto Query preload with a query.

secure_preload.ex

@spec author_query() :: Ecto.Query.t()
  def author_query() do
    from user in User,
    select: [:name, :email]
  end
@spec query_active_charter_sessions(integer(), NaiveDateTime.t()) :: Ecto.Query.t()
  def query_active_charter_sessions(charter_id, active_threshold) do
    from(s in Session,
      join: c in Charter,
      on: c.id == s.charter_id,
      where: c.id == ^charter_id,
      where: ^active_threshold <= s.inserted_at,
      preload: author: ^author_query()
    )
  end
  
  %Testivator.SRM.Session{
    __meta__: #Ecto.Schema.Metadata<:loaded, "sessions">,
    author: %Testivator.URM.User{
      __meta__: #Ecto.Schema.Metadata<:loaded, "users">,
      activation_token: nil,
      activation_token_activated_at: nil,
      activation_token_expires_at: nil,
      auth_tokens: #Ecto.Association.NotLoaded<association :auth_tokens is not loaded>,
      charters: #Ecto.Association.NotLoaded<association :charters is not loaded>,
      current_sign_in_at: nil,
      current_sign_in_ip: nil,
      email: "[email protected]",
      id: nil,
      inserted_at: nil,
      last_sign_in_at: nil,
      last_sign_in_ip: nil,
      name: "Samanta Gorczany",
      new_password: nil,
      password: nil,
      password_hash: nil,
      password_reset_token: nil,
      password_reset_token_expires_at: nil,
      profile: #Ecto.Association.NotLoaded<association :profile is not loaded>,
      project: #Ecto.Association.NotLoaded<association :project is not loaded>,
      reports: #Ecto.Association.NotLoaded<association :reports is not loaded>,
      role: #Ecto.Association.NotLoaded<association :role is not loaded>,
      role_id: nil,
      session: #Ecto.Association.NotLoaded<association :session is not loaded>,
      updated_at: nil
    },