Go
Summary - database/sql
Combine Query and Transaction to write a user record.
database/sql summary
In this group you registered a driver with _, set up the pool with sql.Open + Ping, ran queries with Query/QueryRow/Exec, wrote safe queries with placeholders and Prepare, and managed transactions with Begin/Commit/Rollback.
Three habits: don't forget rows.Close() and rows.Err(), never concatenate input into SQL, and always use tx inside a transaction.
A repository layer
In real applications SQL code is gathered in a repository type; the rest of the code only sees its methods:
type UrunRepo struct{ db *sql.DB }
func (r UrunRepo) Ad(id int) (string, error) {
var ad string
err := r.db.QueryRow("SELECT ad FROM urunler WHERE id = ?", id).Scan(&ad)
return ad, err
}
In tests this type can be replaced by an interface and tried with fake data.
Exercise Repository interface
Define type UrunRepo interface { Ad(id int) (string, error) }. Write the Ad method for a map-based type memRepo map[int]string (return errors.New("yok") if missing). Print r.Ad(1) with var r UrunRepo = memRepo{1: "Kalem"}.
Show example solution
package main
import (
"errors"
"fmt"
)
type UrunRepo interface {
Ad(id int) (string, error)
}
type memRepo map[int]string
func (m memRepo) Ad(id int) (string, error) {
ad, ok := m[id]
if !ok {
return "", errors.New("yok")
}
return ad, nil
}
func main() {
var r UrunRepo = memRepo{1: "Kalem"}
fmt.Println(r.Ad(1))
}
Test yourself
-
Why check <code>rows.Err()</code> after the loop?
- To tell whether Next returned false because of an error or the end
- To get the row count
- To open a transaction
- To close the connection
Show answer
To tell whether Next returned false because of an error or the end — Next returns false both at the end and on a read error; rows.Err() tells the difference.
-
Scan the results
var ad string
err := db.QueryRow("SELECT ad FROM urunler WHERE id = ?", 3).____(&ad)
Show answer
var ad string
err := db.QueryRow("SELECT ad FROM urunler WHERE id = ?", 3).Scan(&ad)
-
Group summary
- sql.Open + Ping
- Pool and connection test
- Query + rows.Next
- Reading many rows
- ? / $1
- Safe parameter
- Begin / Commit
- All-or-nothing work
Next lesson: The middleware concept
