udemy-go-web-1/test_connect/main.go

package main

import (
	"database/sql"
	"fmt"
	"log"
	"net/smtp"
	"os"

	_ "github.com/jackc/pgx/v5/stdlib"
)

func main() {
	// connect to a database
	conn, err := sql.Open("pgx", fmt.Sprintf("host=localhost port=5432 dbname=test_connect user=%s password=%s", os.Getenv("PGUSER"), os.Getenv("PGPWD")))
	if err != nil {
		log.Fatalf("Unable to connect to the database: %v\n", err)
	}
	defer conn.Close()

	// Send test email
	from := "me@here.com"
	auth := smtp.PlainAuth("", from, "", "localhost")
	_ = smtp.SendMail("localhost:1025", auth, from, []string{"you@there.com"}, []byte("Hello world"))

	log.Println("Connected to database!")

	// test my connection
	err = conn.Ping()
	if err != nil {
		log.Fatal("Cannot ping database!")
	}

	log.Println("Pinged database!")

	// get rows from table
	err = getAllRows(conn)
	if err != nil {
		log.Fatal(err)
	}

	// insert a row
	query := `insert into users (first_name, last_name) values ($1, $2)`
	_, err = conn.Exec(query, "Jack", "Brown")
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Inserted a row!")

	// get rows from table again
	err = getAllRows(conn)
	if err != nil {
		log.Fatal(err)
	}

	// update a row
	stmt := `update users set first_name = $1 where first_name = $2`
	_, err = conn.Exec(stmt, "Jackie", "Jack")
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Updated one or more rows")

	// get rows from table again
	err = getAllRows(conn)
	if err != nil {
		log.Fatal(err)
	}

	// get one row by id
	var firstName, lastName string
	var id int

	query = `select id, first_name, last_name from users where id = $1`
	row := conn.QueryRow(query, 1)

	err = row.Scan(&id, &firstName, &lastName)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Query row returns", id, firstName, lastName)

	// delete a row
	query = `delete from users where id = $1`
	_, err = conn.Exec(query, 3)
	if err != nil {
		log.Fatal(err)
	}

	log.Println("Delete a row")

	// get rows again
	err = getAllRows(conn)
	if err != nil {
		log.Fatal(err)
	}
}

func getAllRows(conn *sql.DB) error {
	rows, err := conn.Query("select id, first_name, last_name from users")
	if err != nil {
		log.Println(err)
		return err
	}
	defer rows.Close() // IMPORTANT!!

	var firstName, lastName string
	var id int

	for rows.Next() {
		err := rows.Scan(&id, &firstName, &lastName)
		if err != nil {
			log.Println(err)
			return err
		}
		fmt.Println("Record is", id, firstName, lastName)
	}

	if err = rows.Err(); err != nil {
		log.Fatalf("Error scanning rows: %v", err)
	}

	fmt.Println("----------------------------")

	return nil
}