Can't set up has-many association in GORM - go

Question

I'm trying to set up an association between Users and PredictionsBags. My problem is that everything works OK if I use GORM's assumed names for referring objects, but I'd like to change the names a bit.
type User struct {
gorm.Model
// We’ll try not using usernames for now
Email string `gorm:"not null;unique_index"`
Password string `gorm:"-"`
PasswordHash string `gorm:"not null"`
Remember string `gorm:"-"` // A user’s remember token.
RememberHash string `gorm:"not null;unique_index"`
Bags []PredictionsBag
}
Every user, of course, owns zero or more PredictionsBags:
type PredictionsBag struct {
gorm.Model
UserID uint // I want this to be "OwnerID"
Title string
NotesPublic string `gorm:"not null"` // Markdown field. May be published.
NotesPrivate string `gorm:"not null"` // Markdown field. Only for (private) viewing and export.
Predictions []Prediction
}
And I'd like to have .Related() work in the usual way:
func (ug *userGorm) ByEmail(email string) (*User, error) {
var ret User
matchingEmail := ug.db.Where("email = ?", email)
err := first(matchingEmail, &ret)
if err != nil {
return nil, err
}
var bags []PredictionsBag
if err := ug.db.Model(&ret).Related(&bags).Error; err != nil {
return nil, err
}
ret.Bags = bags
return &ret, nil
}
My problem is that I can't find a way to change PredictionsBag.UserID to anything else and still have GORM figure out the relationships involved. I've been reading http://gorm.io/docs/has_many.html#Foreign-Key and if I change the relevant lines to
type User struct {
// …
Bags []PredictionsBag `gorm:"foreignkey:OwnerID"`
}
and
type PredictionsBag struct {
// …
OwnerID uint
// …
}
I get this error:
[2019-07-28 14:23:49] invalid association []
What am I doing wrong? I've also been reading http://gorm.io/docs/belongs_to.html, but I'm not sure which page to follow more closely.

Answer 1

I'll have to Check Related() when I get home, but I think what you're looking for is Preload() This is my example that works with what you want.
package main
import (
"errors"
"fmt"
_ "github.com/go-sql-driver/mysql"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/mysql"
"log"
)
var DB *gorm.DB
func init() {
var err error
DB, err = gorm.Open("mysql", fmt.Sprintf("%s:%s#tcp(%s:3306)/%s?&parseTime=True&loc=Local", "root", "root", "localhost", "testing"))
if err != nil {
log.Fatal(err)
}
DB.DropTableIfExists(&User{}, &PredictionsBag{})
DB.AutoMigrate(&User{}, &PredictionsBag{})
user := User{Email:"dave#example.com"}
user.Bags = append(user.Bags, PredictionsBag{OwnerID: user.ID, NotesPrivate: "1", NotesPublic: "1"})
DB.Create(&user)
}
func main() {
user := User{Email:"dave#example.com"}
err := user.ByEmail()
if err != nil {
log.Println(err)
}
fmt.Println(user.ID, user.Email, "Bags:", len(user.Bags))
DB.Close()
}
type User struct {
gorm.Model
// We’ll try not using usernames for now
Email string `gorm:"not null;unique_index"`
Password string `gorm:"-"`
PasswordHash string `gorm:"not null"`
Remember string `gorm:"-"` // A user’s remember token.
RememberHash string `gorm:"not null;unique_index"`
Bags []PredictionsBag `gorm:"foreignkey:OwnerID"`
}
type PredictionsBag struct {
gorm.Model
OwnerID uint
Title string
NotesPublic string `gorm:"not null"` // Markdown field. May be published.
NotesPrivate string `gorm:"not null"` // Markdown field. Only for (private) viewing and export.
}
func (ug *User) ByEmail() error {
DB.Where("email = ?", ug.Email).Preload("Bags").Limit(1).Find(&ug)
if ug.ID == 0 {
return errors.New("no user found")
}
return nil
}
Using this might work with related, but I'm not sure what else needs to be changed:
Bags []PredictionsBag `gorm:"foreignkey:OwnerID;association_foreignkey:ID"`
Update:
I can get the Related() method to work, if you state the ForeignKey like the following:
DB.Where("email = ?", ug.Email).Limit(1).Find(&ug)
if ug.ID == 0 {
return errors.New("no user found")
}
if err := DB.Model(&ug).Related(&ug.Bags, "owner_id").Error; err != nil {
return err
}