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@alexedwards
Last active May 22, 2024 13:58
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.
├── books
│   ├── handlers.go
│   └── models.go
├── config
│   └── db.go
└── main.go
package config
import (
"database/sql"
_ "github.com/lib/pq"
)
type Env struct {
DB *sql.DB
}
func NewDB(dataSourceName string) (*sql.DB, error) {
db, err := sql.Open("postgres", dataSourceName)
if err != nil {
return nil, err
}
err = db.Ping()
if err != nil {
db.Close()
return nil, err
}
return db, nil
}
package books
import (
"bookstore/config"
"fmt"
"net/http"
)
func BooksIndex(env *config.Env) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
if r.Method != "GET" {
http.Error(w, http.StatusText(405), 405)
return
}
bks, err := AllBooks(env.DB)
if err != nil {
http.Error(w, http.StatusText(500), 500)
return
}
for _, bk := range bks {
fmt.Fprintf(w, "%s, %s, %s, £%.2f\n", bk.Isbn, bk.Title, bk.Author, bk.Price)
}
})
}
package main
import (
"bookstore/books"
"bookstore/config"
"log"
"net/http"
)
func main() {
db, err := config.NewDB("postgres://user:pass@localhost/bookstore")
if err != nil {
log.Panic(err)
}
defer db.Close()
env := &config.Env{DB: db}
http.Handle("/books", books.BooksIndex(env))
http.ListenAndServe(":3000", nil)
}
package books
import (
"database/sql"
)
type Book struct {
Isbn string
Title string
Author string
Price float32
}
func AllBooks(db *sql.DB) ([]*Book, error) {
rows, err := db.Query("SELECT * FROM books")
if err != nil {
return nil, err
}
defer rows.Close()
bks := make([]*Book, 0)
for rows.Next() {
bk := new(Book)
err := rows.Scan(&bk.Isbn, &bk.Title, &bk.Author, &bk.Price)
if err != nil {
return nil, err
}
bks = append(bks, bk)
}
if err = rows.Err(); err != nil {
return nil, err
}
return bks, nil
}
@mlevkov
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mlevkov commented May 27, 2018

a concrete example with logging and middleware would have been nice. I would not want to instantiate the data elements in every package, but rather pass them around once initiated.

@TFiroozian
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Have you seen the interface way? what if I want to have multiple packages in interface way .Should I make a config package as same as here?

@avoidik
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avoidik commented Oct 2, 2022

as far I can see there is an edge case in error handling in NewDB function which wasn't covered in this sample, as well as in the book, I'm talking about this code

func NewDB(dataSourceName string) (*sql.DB, error) {
	db, err := sql.Open("postgres", dataSourceName)
	if err != nil {
		return nil, err
	}
	if err = db.Ping(); err != nil {
		return nil, err
	}
	return db, nil
}

shouldn't it be like this?

func NewDB(dataSourceName string) (*sql.DB, error) {
	db, err := sql.Open("postgres", dataSourceName)
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			db.Close()
		}
	}()

	err = db.Ping()
	if err != nil {
		return nil, err
	}
	return db, nil
}

I understand that it's still a low-plausible case when db.Ping may fail, but still

@alexedwards
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Author

@avoidik You're right, thanks for spotting that. I've updated the Gist (and the books too) 👍

@ThatIknow
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ThatIknow commented May 14, 2024

@avoidik

Nice catch. Although, If the function were more bulky than it was then this style would be beneficial. But as it is, wouldn't it be cleaner to just do

......
......
if err != nil {
db.Close()
return nil, err
}

....

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