从带有gorm的两个表中选择

I'm using gorm and postgresql for a side-project, and I don't know how to solve this problem in 1 request:

My User type is the following:

type User struct {
    UserId    string
    Email     string
    FirstName string
    LastName  string
    Phone     string
    Address_1 string
    Address_2 string
    City      string
    State     string
    Zip       string
    Gender    string
    ImageUri  string
    Roles     []Role `gorm:"foreignkey:UserId"`
}

My Role type is the following:

type Role struct {
    UserId string
    Role   string
}

I want to get all users with their associated roles, but right now i'm doing this with 2 requests and I want to do it only with one:

func (s *Store) ListUsers() ([]User, error) {
    users := []User{}
    if err := db.Joins("join roles ON roles.user_id = users.user_id").Find(&users).Error; err != nil {
        return nil, err
    }

    for i, user := range users {
        roles := []Role{}
        if err := db.Where("user_id = ?", user.UserId).Model(&Role{}).Find(&roles).Error; err != nil {
            return User{}, errors.Wrap(err, "failed to get roles")
        }
        users[i].Roles = roles
    }

    return users, nil
}

I tried with several different requests, using Related etc... but my Roles slice is always empty. Any ideas ?

[EDIT] My sql schema

CREATE TABLE IF NOT EXISTS users (
  user_id varchar PRIMARY KEY UNIQUE NOT NULL,
  email varchar UNIQUE NOT NULL,
  first_name varchar,
  last_name varchar,
  phone varchar,
  address_1 varchar,
  address_2 varchar,
  city varchar,
  state varchar,
  zip varchar,
  gender varchar,
  image_uri varchar
);

CREATE TABLE IF NOT EXISTS roles (
  user_id varchar REFERENCES users (user_id) ON DELETE CASCADE,
  role varchar NOT NULL
);

There @har07 soultions it's probably what you need db.Preload("Roles").Find(&users) but you can't get Roles because you don't have primary key declared in you user struct, so at the end your user should look like this:

type User struct {
    UserId    string `gorm:"primary_key"`
    Email     string
    FirstName string
    LastName  string
    Phone     string
    Address_1 string
    Address_2 string
    City      string
    State     string
    Zip       string
    Gender    string
    ImageUri  string
    Roles     []Role `gorm:"foreignkey:UserId"`
}