Exemplo de uso da função `StructScan` do pacote sqlx

1_create_tables.down.sql

DROP TABLE IF EXISTS items;
DROP TABLE IF EXISTS categories;
DROP TABLE IF EXISTS menus;

1_create_tables.up.sql

CREATE TABLE IF NOT EXISTS menus (
	id SERIAL PRIMARY KEY,
	name VARCHAR NOT NULL UNIQUE,
	description VARCHAR
);

CREATE TABLE IF NOT EXISTS categories (
	id SERIAL PRIMARY KEY,
	name VARCHAR NOT NULL UNIQUE,
	menu_id INTEGER NOT NULL,
	CONSTRAINT fk_menu FOREIGN KEY (menu_id)
		REFERENCES menus (id) MATCH SIMPLE
		ON UPDATE RESTRICT
		ON DELETE RESTRICT
);

CREATE TABLE IF NOT EXISTS items (
	id SERIAL PRIMARY KEY,
	name VARCHAR NOT NULL UNIQUE,
	description VARCHAR,
	category_id INTEGER,
	CONSTRAINT fk_category FOREIGN KEY (category_id)
		REFERENCES categories (id) MATCH SIMPLE
		ON UPDATE RESTRICT
		ON DELETE RESTRICT
);

2_insert_data.down.sql

TRUNCATE TABLE items CASCADE;
TRUNCATE TABLE categories CASCADE;
TRUNCATE TABLE menus CASCADE;

2_insert_data.up.sql

INSERT INTO menus (name, description) VALUES
    ('Comidas', 'Coisas de mastigar'),
    ('Bebidas', 'Coisas de beber'),
    ('Sobremesas', 'Coisas de engordar')
;

INSERT INTO categories (name, menu_id) VALUES
    ('Massas', (SELECT id FROM menus WHERE name = 'Comidas')),
    ('Risotos', (SELECT id FROM menus WHERE name = 'Comidas')),
    ('Caldos', (SELECT id FROM menus WHERE name = 'Comidas')),
    ('Sucos', (SELECT id FROM menus WHERE name = 'Bebidas')),
    ('Refrigerantes', (SELECT id FROM menus WHERE name = 'Bebidas')),
    ('Drinks e coquetéis', (SELECT id FROM menus WHERE name = 'Bebidas')),
    ('Doces', (SELECT id FROM menus WHERE name = 'Sobremesas')),
    ('Sorvetes', (SELECT id FROM menus WHERE name = 'Sobremesas'))
;

INSERT INTO items (name, category_id) VALUES
    ('Lasanha', (SELECT id FROM categories WHERE name = 'Massas')),
    ('Nhoque', (SELECT id FROM categories WHERE name = 'Massas')),
    ('Ravioli', (SELECT id FROM categories WHERE name = 'Massas')),
    ('Camarão', (SELECT id FROM categories WHERE name = 'Risotos')),
    ('Funghi', (SELECT id FROM categories WHERE name = 'Risotos')),
    ('Caldo verde', (SELECT id FROM categories WHERE name = 'Caldos')),
    ('Canja', (SELECT id FROM categories WHERE name = 'Caldos')),
    ('Limão', (SELECT id FROM categories WHERE name = 'Sucos')),
    ('Laranja', (SELECT id FROM categories WHERE name = 'Sucos')),
    ('Soda', (SELECT id FROM categories WHERE name = 'Refrigerantes')),
    ('Capeta', (SELECT id FROM categories WHERE name = 'Drinks e coquetéis')),
    ('Caipirosca', (SELECT id FROM categories WHERE name = 'Drinks e coquetéis')),
    ('Leite', (SELECT id FROM categories WHERE name = 'Doces')),
    ('Mamão', (SELECT id FROM categories WHERE name = 'Doces')),
    ('Coco', (SELECT id FROM categories WHERE name = 'Sorvetes')),
    ('Chocolate', (SELECT id FROM categories WHERE name = 'Sorvetes'))
;

main.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/jmoiron/sqlx"
	_ "github.com/lib/pq"
)

type defaultModel struct {
	ID   uint64 `db:"id" json:"id,omitempty"`
	Name string `db:"name" json:"name"`
	Timestamps
}

type Timestamps struct {
	CreatedAt *time.Time `db:"createdAt,omitempty" json:"createdAt,omitempty"`
	DeletedAt *time.Time `db:"deletedAt,omitempty" json:"deletedAt,omitempty"`
}

type Menu struct {
	defaultModel
	Description *string `db:"description" json:"description,omitempty"`
}

type Category struct {
	defaultModel
	Description *string `db:"description" json:"description,omitempty"`
	Menu        Menu    `db:"menu" json:"menu"`
}

type Item struct {
	defaultModel
	Description *string  `db:"description" json:"description,omitempty"`
	Category    Category `db:"category" json:"category,omitempty"`
}

func listItems(db *sqlx.DB) ([]Item, error) {
	query := `SELECT
		categories.id AS "category.id",
		categories.name AS "category.name",
		menus.id AS "category.menu.id",
		menus.name AS "category.menu.name",
		items.id,
		items.name,
		items.description
	FROM
		menus INNER JOIN categories ON menus.id = categories.menu_id
		INNER JOIN items ON items.category_id = categories.id
	ORDER BY
		items.name`

	rows, err := db.Queryx(query)
	if err != nil {
		return nil, err
	}
	items := []Item{}
	for rows.Next() {
		item := new(Item)
		if err := rows.StructScan(item); err != nil {
			log.Println(err)
			return nil, err
		}
		items = append(items, *item)
	}
	if err := rows.Close(); err != nil {
		log.Println(err)
		return nil, err
	}
	return items, nil
}

func main() {
	dsn := fmt.Sprintf("postgres://%s:%s@%s:%s/%s?sslmode=disable", os.Getenv("DB_USER"), os.Getenv("DB_PASS"), os.Getenv("DB_HOST"), os.Getenv("DB_PORT"), os.Getenv("DB_NAME"))
	db, err := sqlx.Open("postgres", dsn)
	if err != nil {
		log.Fatalln(err)
	}
	defer db.Close()

	items, err := listItems(db)
	if err != nil {
		log.Fatalln(err)
	}

	enc := json.NewEncoder(os.Stdin)
	enc.SetIndent("", "  ")
	if err := enc.Encode(items); err != nil {
		log.Fatalln(err)
	}
}

O exemplo esta muito bom mas usando SQLX podemos diminuir ligeiramente o tamanho da função listItens usando a função db.Select ;)

func listItems(db *sqlx.DB) ([]Item, error) {
	query := `SELECT
		categories.id AS "category.id",
		categories.name AS "category.name",
		menus.id AS "category.menu.id",
		menus.name AS "category.menu.name",
		items.id,
		items.name,
		items.description
	FROM
		menus INNER JOIN categories ON menus.id = categories.menu_id
		INNER JOIN items ON items.category_id = categories.id
	ORDER BY
		items.name`

	items := []Item{}
	err := db.Select(&items, query)
	return items, err
}

Genial! Diminui bastante!