Small tips in Go

Go

Use the underscore to make your numbers readable

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package main

import "fmt"

func main() {
    number := 10000000
    better := 10_000_000

    fmt.Println(number == better)
}

Passing the same argument multiple times to fmt.Printf

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package main

import "fmt"

func main() {
    name := "Bob"
    fmt.Printf("My name is %[1]s. Yes, you heard that right: %[1]s\n", name)
}

avoid deadlock in database

func GetListFollows will not release a connection in database connection pool before rows.Close, so in the
call of func GetUserDetail, there is a new need of connection, but what if every GetUserDetail is waiting
for a new connection and there is no idle connection, as the connection pool is fixed? Then there is a deadlock.

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func GetListFollows(ctx context.Context, id int) ([]*User, error) {
	users := []*User{}
	query := "SELECT source_id, target_id FROM follows where source_id = ?"
	rows, err := sqlDB.QueryContext(ctx, query, id)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil, nil
		}
		return nil, err
	}
	defer rows.Close()

	for rows.Next() {
		follow := &Follow{}
		if err := rows.Scan(&follow.SourceID, &follow.TargetID); err != nil {
			return nil, err
		}

		user, err := GetUserDetail(ctx, follow.TargetID)
		if err != nil {
			return nil, err
		}

		users = append(users, user)
	}

	return users, nil
}
func GetUserDetail(ctx context.Context, id int) (*User, error) {
	user := &User{}
	query := "SELECT id, name, username, bio FROM users WHERE id = ?"
	row := sqlDB.QueryRowContext(ctx, query, id)
	err := row.Scan(&user.ID, &user.Name, &user.UserName, &user.Bio)
	if err != nil {
		if err == sql.ErrNoRows {
			return nil, nil
		}
		return nil, err
	}

	return user, nil
}