Простейшее CRUD приложение Go (вариант 2)

functions.go

package main

func getProducts() ([]Product, error) {
	rows, err := db.Query("SELECT id, name, price FROM products")
	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var products []Product
	for rows.Next() {
		var p Product
		if err := rows.Scan(&p.ID, &p.Name, &p.Price); err != nil {
			return nil, err
		}
		products = append(products, p)
	}

	return products, rows.Err()
}

func getProduct(id int) (Product, error) {
	var p Product

	row := db.QueryRow("SELECT id, name, price FROM products WHERE id = ?", id)
	if err := row.Scan(&p.ID, &p.Name, &p.Price); err != nil {
		return p, err
	}

	return p, nil
}

func createProduct(p Product) (int, error) {
	result, err := db.Exec(
		"INSERT INTO products (name, price) VALUES (?, ?)",
		p.Name, p.Price,
	)
	if err != nil {
		return 0, err
	}

	id, err := result.LastInsertId()
	if err != nil {
		return 0, err
	}

	return int(id), nil
}

func updateProduct(id int, p Product) error {
	_, err := db.Exec(
		"UPDATE products SET name = ?, price = ? WHERE id = ?",
		p.Name, p.Price, id,
	)
	return err
}

func deleteProduct(id int) error {
	_, err := db.Exec("DELETE FROM products WHERE id = ?", id)
	return err
}

main.go

package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"strconv"

	_ "github.com/go-sql-driver/mysql"
)

var db *sql.DB

func main() {
	var err error
	db, err = sql.Open("mysql", "user:password@/dbname")
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	http.HandleFunc("/products", productsHandler)
	http.HandleFunc("/product/", productHandler)

	// Тут указано 8080 потому, что приложениям запущенным от обычного пользователя
	// на уровне операционной системы запрещено работать с портами, номер которых
	// меньше чем 1024
	log.Fatal(http.ListenAndServe(":8080", nil))
}

func productsHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method == http.MethodGet {
		products, err := getProducts()
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		json.NewEncoder(w).Encode(products)
	} else if r.Method == http.MethodPost {
		var p Product
		err := json.NewDecoder(r.Body).Decode(&p)
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
		id, err := createProduct(p)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		fmt.Fprintf(w, "New product ID: %d", id)
	} else {
		http.Error(w, "Invalid request method", http.StatusMethodNotAllowed)
	}
}

func productHandler(w http.ResponseWriter, r *http.Request) {
	id, err := strconv.Atoi(r.URL.Path[len("/product/"):])
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	switch r.Method {
	case http.MethodGet:
		p, err := getProduct(id)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		json.NewEncoder(w).Encode(p)
	case http.MethodPut:
		var p Product
		err := json.NewDecoder(r.Body).Decode(&p)
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}
		err = updateProduct(id, p)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		fmt.Fprintf(w, "Product ID: %d updated", id)
	case http.MethodDelete:
		err := deleteProduct(id)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		fmt.Fprintf(w, "Product ID: %d deleted", id)
	default:
		http.Error(w, "Invalid request method", http.StatusMethodNotAllowed)
	}
}

model.go

package main

type Product struct {
	ID    int     `json:"id"`
	Name  string  `json:"name"`
	Price float64 `json:"price"`
}