我是来自python背景的Golang的新手，所以尝试了解新的和不同的概念。我正在尝试创建相关字段，然后从数据库中选择它们。

楷模：

type Company struct {
    gorm.Model
    Name string
}

type CreditCard struct {
    gorm.Model
    Number    int
    Company   Company
    CompanyId uint
}

type User struct {
    gorm.Model
    Name         string
    CreditCard   CreditCard
    CreditCardID uint
}

创建表和行并从数据库中选择

common.DB.AutoMigrate(
    &Company{},
    &CreditCard{},
    &User{},
)

user := User{
    Name:       "Alice",
    CreditCard: CreditCard{Number: 123456, Company: Company{Name: "Bank A"}},
}

common.DB.Create(&user)

var retrivedUser User
var creditCard CreditCard
var company Company
common.DB.First(&retrivedUser, 1).Related(&creditCard).Related(&company)

fmt.Println("user name", retrivedUser.Name)
fmt.Println("creditcard number", retrivedUser.CreditCard.Number)
fmt.Println("creditcard number related", creditCard.Number)
fmt.Println("company name", retrivedUser.CreditCard.Company.Name)
fmt.Println("company name related", company.Name)

打印：

user name Alice
creditcard number 0
creditcard number related 123456
company name 
company name related

两个问题：

1. 为什么我需要选择RelatedcreditCard作为单独的变量而不是使用点符号？
2. 我invalid association []在Related公司上遇到错误，并且没有点符号或相关工作。我该如何取回？