Are possible to make db.Preload() in GORM to be Auto-preload? - go

Question

model.go:
type First struct {
ID int `json:"id" gorm:"column:id;primary_key"`
Status string `json:"status" gorm:"column:status"`
SecondID int `json:"second_id" gorm:"column:second_id"`
SecondData Second `json:"second_data" gorm:"foreignKey:SecondID;references:ID"`
}
type Second struct {
ID int `json:"id" gorm:"column:second_id;primary_key"`
Status string `json:"status" gorm:"column:status"`
Description string `json:"description" gorm:"column:description"`
}
var res []model.First
db.Raw("first.*, second.* FROM first LEFT JOIN second ON first.second_id = second.second_id")
db.Preload("SecondData").Find(&res).Error
Output:
{
"id": 1,
"status": "A",
"second_id": 1
"second_data": {
"id": 1
"status": "B",
"description": "blablabla"
}
}
I don't really know how db.Preload() works. Why i should use db.Preload() to get "SecondData" every time i need do nested struct ? Are it's possible only use db.Row() or db.Table().Joins().Where().Find(), i mean's without db.Preload()?

Answer 1

If you want SecondData loaded every time when the First struct is loaded without using Preload, you might consider using hooks.
It might look something like this:
func (f *First) AfterFind(tx *gorm.DB) error {
return tx.First(&f.SecondData, f.SecondID).Error
}
So, when you load the First data, the AfterFind hook should be triggered.