GORM create record with foreign key

Can't make record that refers to existed row.

I have two tables and one table references on another one. Table "Category" is already existed. I try to add new record on "Heritage" table but gorm try to do new record at Category.

type Category struct {
	gorm.Model
	Name string `gorm:"unique"`
}

type Site struct {
	gorm.Model
	Category         Category `gorm:"foreignkey:CategoryID"`
	DateInscribed    string
	HttpURL          string
	Latitude         float32
	Location         string
	Longitude        float32
	SecondaryDates   string
	ShortDescription string
	Site             string
}

As I say "Category" table is existed with all I needed rows. I try to do Site record but get issue "define a valid foreign key for relations or implement the Valuer/Scanner interface".

With this code I try to make record.

site := &models.Site{
	Category:         models.Category{Name: heritage.Category},
	DateInscribed:    heritage.DateInscribed,
	HttpURL:          heritage.HttpURL,
	Latitude:         heritage.Latitude,
	Location:         heritage.Location,
	Longitude:        heritage.Longitude,
	SecondaryDates:   heritage.SecondaryDates,
	ShortDescription: heritage.ShortDescription,
}

db.Create(site)

Seems I try to make new record on Category table but needed only add category_id value to Site record.

Normally you don't store the Name as a foreign key, but the ID value.
For that you need to add a new field CategoryID in Site of type uint:

type Site struct {
    gorm.Model
    Category         Category
    CategoryID       uint
    DateInscribed    string
    ...
}

This field will be automatically linked to the Category table, so if you use the default name, you don't need to write gorm:"foreignKey:CategoryID".

Then to create a Site object, you can do it in this way:

site := &models.Site{
	CategoryID: id,
    DateInscribed:    heritage.DateInscribed,
    ...
}
db.Create(site)

If you want to reuse the existing table Category, you will need to find the ID from name:

var id uint
db.Model(&models.Category{}).Where("name = ?", name).Select("ID").First(&id)

For me it is not clear from the GORM documentation what to do if you want to reference the Name field, maybe someone else can answer.

Hope this helps.