Golang GORM has_many exemple

hasmany.go

package main

import (
	"fmt"
	"log"

	"github.com/Sirupsen/logrus"
	"github.com/jinzhu/gorm"
	_ "github.com/jinzhu/gorm/dialects/postgres"
)

var (
	DB *gorm.DB
)

type Topic struct {
	gorm.Model
	// TopicID uint `gorm:"primary_key"`
	Name    string
	Posts   []Post `gorm:"ForeignKey:ID"`
}

type Post struct {
	gorm.Model
	// PostID     uint `gorm:"primary_key"`
	Title      string
	TopicRefer uint `gorm:"column:id`
}

func main() {
	var err error
	dbConnect()
	// DB.LogMode(true)
	defer DB.Close()

	DB.AutoMigrate(&Topic{}, &Post{})
	model := Topic{}
	// DB.Model(&model).Related(&model.Posts, "TopicRefer")
	DB.Model(&model).Related(&model.Posts, "TopicRefer")
	defer DB.DropTable(&Topic{}, &Post{})
	DB.LogMode(true)

	// Create Topic Finance
	t := &Topic{Name: "Finance"}
	err = DB.Model(&Topic{}).Create(t).Error
	if err != nil {
		log.Fatal("Error creating topic finance: ", err)
	}

	// Create Post about blockchain
	p := &Post{Title: "blockchain", TopicRefer: 1}

	// Associate Post to Topic
	res := DB.Model(t).Association("Posts").Append(p)
	if res.Error != nil {
		log.Fatal("Can't attach post to topic: ", res.Error)
	}
	fmt.Printf(" Associate post to topic: %+v\n", res)

	// Get first Topic
	topic := Topic{}
	err = DB.Model(topic).First(&topic).Related(&topic.Posts, "TopicRefer").Error
	if err != nil {
		log.Fatal("Error getting topic: ", err)
	}

	// Print Topic
	fmt.Println("Topics: ", topic, topic.Posts)
	if len(topic.Posts) > 0 {
		fmt.Println("\n\n------ ITS WORKED !!!!! ------")
	}

	DB.LogMode(false)
}

func dbConnect() {
	var err error
	logrus.Print("DB connecting...")
	pgURL := fmt.Sprintf("postgresql://%s:%s@%s:%s/%s?sslmode=%v", "dev", "dev", "172.16.239.135",
		"5432", "dev", "disable")

	DB, err = gorm.Open("postgres", pgURL)
	if err != nil {
		logrus.Fatal("Error connecting postgres: ", err)
	}
	logrus.Print("DB connected")
}