tech_blog_20220405_2.scala

val userSeq: Seq[User] = UserRepository.findAll();
val groupSeq: Seq[Group] = GroupRepository.findAll();
val groupMemberSeq: Seq[GroupMember] = GroupMembersRepository.findAll();
val result: Seq[UserView] = userSeq.map(user => { // ①
  val groupIdSeq: Seq[GroupId] =
    groupMemberSeq
      .filter(_.userId == user.id) // ②
      .map(_.groupId)
val userGroups: Seq[Group] = // ③
    groupSeq.filter(group =>
      groupIdSeq.contains(group.id)
    )
    
  UserView(
    user.id,
    user.name,
    userGroups
  )
})