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@alexedwards
Last active April 23, 2024 20:05
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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
}
@harlow
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harlow commented Aug 2, 2016

Great example @alexedwards. If you're logging from Middleware how would you handle the call chain so Env is avail in the middleware too?

@nkumar15
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nkumar15 commented Jun 17, 2017

Any suggestion on @harlow question? I am also thinking about this question. What if I want to share logger object in middleware and data access functions?

@hypnoglow
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@nkumar15 What is the problem?
This will work since BooksIndex(env) returns http.Handler.
And you can pass logger directly to the middleware.

http.Handle("/books", loggerMiddleware(books.BooksIndex(env), env.Logger))
http.ListenAndServe(":3000", nil)

@paracha3
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paracha3 commented Feb 9, 2018

Not clear how (specially where) the db.Close() will be done? I am surprised i don't see defer db.Close() anywhere.
What am i missing?

@aarjan
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aarjan commented Mar 5, 2018

@paracha3, you can defer the db close operation in the main function, just after error check; since it is the root node where db is instantiated.

@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) 👍

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