table references a table which in turn references another table - mysql

Question

I'm using gorm, and I have this structure where the User table contains a foreign key referencing Address, which then references Country.
type User struct {
ID int `gorm:"column:id; primaryKey; autoIncrement" json:"id"`
Address Address
AddressID int `gorm:"column:address_id;foreignKey:AddressID;references:ID" json:"address"`
}
type Address struct {
ID int `gorm:"column:ID;primaryKey;autoIncrement;" json:"id"`
CountryCode int `gorm:"column:country_code; foreignKey:CountryCode; references:Code" json:"country_code"`
Country Country
}
type Country struct {
Code int `gorm:"column:code; primaryKey; autoIncrement" json:"code"`
Name string `gorm:"column:name" json:"name"`
ContinentName string `gorm:"column:continent_name" json:"continentName"`
}
relationship explained in the photo:
Now when I return a user using:
db.Model(&user).Where().First() // or Find()
I get the Address, and Country Empty, like this:
{
ID: 1,
AddressID: 2,
Address: {
// empty address.
}
}
I did create function repopulating the Address and Country records for me, similar to this:
func PopulateUser(user) User {
addr = FindAddresByID(user.ID)
cntr = FindCountryByCode(addr.Code)
addr.Country = cntr
user.Address = addr
return user
}
but my questions:
is there a function in Gorm which can do that for me without me creating the function?
can Associations help in this case?
if I want the address to be deleted when the user deleted, how I can do this in Gorm?
I tried to find answers on my own, but the documentation is a bit messy.

Answer 1

The documentation shows the foreign key tags to go at the struct reference.
i.e in your case those should be at Address and Country instead of AddressID and CountryCode. Something like:
type User struct {
Address Address `gorm:"foreignKey:AddressID;references:ID"`
AddressID int `gorm:"column:address_id"`
}
type Address struct {
CountryCode int `gorm:"column:country_code"`
Country Country gorm:"foreignKey:CountryCode; references:Code"`
}
Please try with those.
For
Please see eager loading here
db.Preload("User").Preload("Address").Find(&users)
You can use cascade tag on the column.
type User struct {
gorm.Model
Name string
CompanyID int
Company Company `gorm:"constraint:OnUpdate:CASCADE,OnDelete:SET NULL;"`
}