关于GORM预加载时, 外键为0, 结果不正确的问题

小弟是新人一名, 使用gorm关联数据后, 发现预加载时, 如果外键的值是0, 则无法加载出数据内容. 求解决方案.

代码如下:

type Profile struct {
    ID    uint `gorm:"primary_key"`
    Refer int
    Name  string
}

type User struct {
    gorm.Model
    Profile   Profile `gorm:"ForeignKey:ProfileID;AssociationForeignKey:Refer"`
    ProfileID int
    Username  string
}

func main() {
    db, err := gorm.Open("sqlite3", "test.db")
    if err != nil {
        panic("failed to connect database")
    }
    defer db.Close()

    db.AutoMigrate(&Profile{}, &User{})

    var pro Profile
    pro.ID = 1
    pro.Refer = 0
    pro.Name = "root"
    db.FirstOrCreate(&pro)

    pro.ID = 2
    pro.Refer = 1
    pro.Name = "user"
    db.FirstOrCreate(&pro)

    pro.ID = 3
    pro.Refer = 2
    pro.Name = "admin"
    db.FirstOrCreate(&pro)

    var user User
    user.ID = 1
    user.ProfileID = 0
    user.Username = "张三"
    db.FirstOrCreate(&user)

    user.ID = 2
    user.ProfileID = 1
    user.Username = "李四"
    db.FirstOrCreate(&user)

    user.ID = 3
    user.ProfileID = 2
    user.Username = "王五"
    db.FirstOrCreate(&user)

    var users []User
    db.Preload("Profile").Find(&users)

    for _, user := range users {
        fmt.Println(user.Profile)
    }

}

输出结果:

1. {0 0 } // 正确时, 这里应该是 {1 0 root}
2. {2 1 user}
3. {3 2 admin}

数据库: