main.go

package models

import (
	"db" //You have a storage layer wich init db and make is available on the namespace
)

type Model interface {
	GetId() string
	SetId(id string)
}

type modelImpl struct {
	id string
}

func (m *modelImpl) SetId(id string) {
	m.id = id
}

func (m *modelImpl) Save(debug bool) {
	if debug {
		db.Debug.Save(&m)
	}else{
		db.Save(&m)
	}
}

user.go

package models

import ("db")

type User struct {
	modelImpl
	UserName string
	FullName string
	Email    string
}

func NewUser(userName, fullName, email string) *User {
	u := &User{
		UserName: userName,
		FullName: fullName,
		Email:    email,
	}
	u.SetId(userName) // lets say names are ids here so we can rewrite GetId
	return u
}

func (u *User) GetId() string {
	return u.UserName
}