Error 1452: Cannot add or update a child row (GOLANG AND MYSQL)

im a golang intern .I have a problem using foreign keys in gorm. im trying to write a crud operation.im using gorm and when using foreign keys the error : Error 1452: Cannot add or update a child row appears.

package migrations

import "gorm.io/gorm"

type Category struct {
   gorm.Model
   ID    uint
   Title string `gorm:"type:varchar(255)"`
   Sort  int
}

package migrations

import "gorm.io/gorm"

type Contents struct {
   gorm.Model
   ID            uint
   CategoryModel Category `gorm:"foreignKey:cat_id"`
   CatId         uint
   Title         string `gorm:"type:varchar(255)"`
   Content       string `gorm:"content,type:varchar(255)"`
}

and i got this error :

> 2022/11/23 14:31:33 /home/channelead/Documents/blog-service-go/internal/activities/blog/Contents/action.go:26 Error 1452: Cannot add or update a child row: a foreign key constraint fails
>
> (service-blog-go.contents, CONSTRAINT fk_contents_category_model FOREIGN KEY (cat_id) REFERENCES categories (id))
[3.247ms] [rows:0] INSERT INTO contents (created_at,updated_at,deleted_at,cat_id,title,content) VALUES ('2022-11-23 14:31:33.972','2022-11-23 14:31:33.972',NULL,0,'khodaya csacas dg','testing ')

Please notice the insert query. You are giving 0 as cat_id which reference the ID of Category table. But there is no entry with 0 ID in Category table. Another important fact is you don’t need ID explicitly if you use gorm.Model because it has a ID field inside. And CategoryModel field should be renamed to Category. These are gorm default but you can configure these things. Please read the documentation. Here is the working code GITHUB LINK. You can clone the repo and run.

package storage
import (
"fmt"
"log"
"gorm.io/driver/sqlite"
"gorm.io/gorm"
"gorm.io/gorm/logger"
)
type Category struct {
gorm.Model
Title string `gorm:"type:varchar(255)"`
Sort  int
}
type Contents struct {
gorm.Model
Category   Category
CategoryID uint
Title      string `gorm:"type:varchar(255)"`
Content    string `gorm:"type:varchar(255)"`
}
func GormTest3() {
db, err := gorm.Open(sqlite.Open("gorm.db"), &gorm.Config{
Logger: logger.Default.LogMode(logger.Info),
})
if err != nil {
log.Fatal("could not open database")
}
err = db.AutoMigrate(&Contents{}, &Category{})
if err != nil {
log.Fatal("could not migrate database")
}
createTestData3(db)
fetchData3(db)
}
func createTestData3(db *gorm.DB) {
category := Category{
Title: "ABC",
Sort:  1,
}
err := db.Create(&category).Error
if err != nil {
fmt.Println("failed to create user data")
}
content := Contents{
CategoryID: category.ID,
Title:      "Good Content Title",
Content:    "Good Content",
}
err = db.Create(&content).Error
if err != nil {
fmt.Println("failed to create user data")
}
}
func fetchData3(db *gorm.DB) {
var cts []Contents
if err := db.Find(&cts).Error; err != nil {
fmt.Println("failed to load post")
}
fmt.Println(cts)
}

Ref: Gorm Has One