tester.go

package main

import (
  "fmt"
  "github.com/jinzhu/gorm"
  _ "github.com/jinzhu/gorm/dialects/sqlite"
)

type Packs []*Pack
type Pack struct {
  ID     uint    `json:"id" gorm:"primary_key"`
  Name   string  `json:"name" sql:"unique_index"`
  Builds *Builds `json:"builds"`
} 

type Builds []*Build
type Build struct {
  ID     uint   `json:"id" gorm:"primary_key"`
  Pack   *Pack  `json:"-"`
  PackID uint   `json:"pack_id" sql:"index"`
  Name   string `json:"name" sql:"unique_index"`
  Mods   *Mods  `json:"mods" gorm:"many2many:build_mods;"`
} 

func main() {
  db, err := gorm.Open("sqlite3", "database.sqlite3")

  if err != nil {
    panic(err)
  }

  db.LogMode(true)
  db.AutoMigrate(&Pack{}, &Build{})

  pack1 := &Pack{Name: "Pack1"}
  db.Create(pack1)
  pack2 := &Pack{Name: "Pack2"}
  db.Create(pack2)
  pack3 := &Pack{Name: "Pack3"}
  db.Create(pack3)

  build1 := &Build{Name: "Build1", Pack: pack1}
  db.Create(build1)
  build2 := &Build{Name: "Build2", Pack: pack1}
  db.Create(build2)
  build3 := &Build{Name: "Build3", Pack: pack1}
  db.Create(build3)

  packs := &Packs{}
  if err := db.Preload("Builds").Find(packs).Error; err != nil {
    fmt.Printf("Failed to fetch packs. ", err)
    return
  }
  fmt.Println(packs)
}