How to preload with nullable ForeignKey - go

Question

I have the following example:
type PostModel struct {
Id int64 `gorm:"primary_key;AUTO_INCREMENT;column:id"`
UserId *int64 `gorm:"column:userId;"`
User UserModel `gorm:"ForeignKey:Id;AssociationForeignKey:UserId"`
}
type UserModel struct {
Id int64 `gorm:"primary_key;AUTO_INCREMENT;column:id"`
}
when I use
db.Model(&model.PostModel{}).Where(where).Preload("User").Find(&post)
I got a Correct reply, but it has something wrong.
SELECT * FROM `user` WHERE (`id` IN (?,?,?,?,?,?,?,?,?,?))[0xc00023dce0 0xc00023dda0 0xc00023d9e0 0xc00023d920 0xc00023daa0 0xc00023db60 0xc00023dc20 0xc00023de60 0xc00023df20 0xc00023d790] 1
All userid are 1, but in gorm sql,it use pointer address to replace number. like 0xc00023dce0 0xc00023dda0 0xc00023d9e0 0xc00023d920 0xc00023daa0 0xc00023db60 0xc00023dc20 0xc00023de60 0xc00023df20 0xc00023d790.
How to fix it?

Answer 1

I wrote a sample code as you described and put Gorm in log mode to see the SQLs but it prints correct SQLs:
[2020-03-29 21:29:42] [0.17ms] SELECT * FROM "post_models"
[4 rows affected or returned ]
[2020-03-29 21:29:42] [0.18ms] SELECT * FROM "user_models" WHERE ("id" IN (1,2,1,3))
[3 rows affected or returned ]
As you see queries are correct.
package main
import (
"fmt"
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/sqlite"
"log"
"os"
)
type PostModel struct {
Id int64 `gorm:"primary_key;column:id"`
UserId *int64 `gorm:"column:userId;"`
User UserModel `gorm:"ForeignKey:UserId"`
}
type UserModel struct {
Id int64 `gorm:"primary_key;column:id"`
}
func preloadingSample() error {
_ = os.Remove("test.db") // Remove file to make sure DB is empty
db, err := gorm.Open("sqlite3", "test.db")
if err != nil {
return fmt.Errorf("open DB failed: %w", err)
}
defer db.Close()
db.LogMode(true)
err = db.AutoMigrate(
&PostModel{},
&UserModel{},
).Error
if err != nil {
return fmt.Errorf("migration failed: %w", err)
}
// Put some sample data in DB
sampleUsers := []UserModel{
{},
{},
{},
}
for idx := range sampleUsers {
err = db.Create(&sampleUsers[idx]).Error
if err != nil {
return fmt.Errorf("failed to create: %w", err)
}
}
samplePosts := []PostModel{
{User: sampleUsers[0]},
{User: sampleUsers[1]},
{User: sampleUsers[0]},
{User: sampleUsers[2]},
}
for idx := range samplePosts {
err = db.Create(&samplePosts[idx]).Error
if err != nil {
return fmt.Errorf("failed to create: %w", err)
}
}
var posts []PostModel
err = db.Preload("User").Find(&posts).Error
if err != nil {
return fmt.Errorf("error in find: %w", err)
}
fmt.Printf("%+v\n", posts)
return nil
}
func main() {
err := preloadingSample()
if err != nil {
log.Fatal(err)
}
}