t.Fatalf("errors happened when create: %v", err)
	}

	user.Languages = []Language{{Code: "zh-CN", Name: "Chinese"}, {Code: "en", Name: "English"}}
	for _, lang := range user.Languages {
		DB.Create(&lang)
	}
	user.Friends = []*User{{Name: "friend-1"}, {Name: "friend-2"}}

	if err := DB.Save(&user).Error; err != nil {
		t.Fatalf("errors happened when update: %v", err)
	}

	var user2 User