在scala的play json中指定嵌套对象

Given this code:

鉴于此代码：

    case class SocialUser(firstName: String, lastName: String)
    case class UserDetails(avatarUrl: String, phone: String)

    // I want to avoid having to specify each SocialUser field one by one but just use the implicit write as stated below
    implicit val socialUserWrites = Json.writes[SocialUser] 
    implicit val userDetailsWrites = Json.writes[UserDetails]
    case class Soc