Connection to sql database on multiple php pages

Question

I am creating a site where several pages need connection to the database to perform their operations, for example, I made a login system, so the user clicks 'login' opens a modal in bootstrap to enter the data. I created the "validaLogin.php" page to do the user checks and put a require "validalogin.php"; on the navbar to call such a page. What happens is the following: within this page I make the connection to the bank to perform the operations, but when I open a page that also needs connection to the bank, the error "connects to MYQL" has already been declared and cannot be redeclared.

In short: Two pages are calling the same connection function with the bank twice and gives the error, there is some way to make a connection only for the whole site?

function conectaAoMySQL(){

  $conn = new mysqli(HOST, USER, PASSWORD, DATABASE);
  
  if ($conn->connect_error)
    throw new Exception('Falha na conexão com o MySQL: ' . $conn->connect_error);

  return $conn;   
}

Answer 1

Whenever multiple pages will perform requests or inclusions choose "require_once" or "include_once" as they avoid duplicate inclusions in cases where a page accidentally tries to call a file 2 times.

Answer 2

Create a connection file instead of a function for this, I will show a way using a functional example

php connection.

<?php
    $servername = "localhost"; /* pode deixar localhost */
    $username = "root"; /* nome do usuario do banco de dados */ 
    $password = "1521128"; /* senha do banco de dados caso exista senao deixa $password = "" */
    $dbname = "meubancodedados"; /* nome do seu banco de dados*/

    // Criando a conexão com o banco de dados
    $conn = new mysqli($servername, $username, $password, $dbname);
    // Checando a conexão com o banco de dados
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    } 
?>

and in the other files you need connection just put this at the beginning of the file

<?php include("conexao.php"); ?>

this way the entire file will have connection to the database being able to have 100 lines as much as 10,000 without having to call the function several times, and, ready you will get connection to all necessary files in a simple way

Answer 3

It follows code from the page "validaLogin.php".

<?php
include("conexaoMysql.php");

session_start();

function filtraEntradaV($dado){
    $dado = trim($dado);
    $dado = stripslashes($dado);
    $dado = htmlspecialchars($dado);
    return $dado;
};  

if($_SERVER["REQUEST_METHOD"] == 'POST'){
    $login = filtraEntradaV($_POST["login"]);
    $senha = filtraEntradaV($_POST["senha"]);


    $sql = "SELECT Login FROM usuario where Login = '$login' and Senha = '$senha' ";
    $resultado = $conn->query($sql);

    if($resultado->num_rows <= 0){
        echo "<script>alert('Dados incorretos')</script>";}
    else
        $_SESSION["login"] = $login;

}


?>

Follow code from the other page

include("conexaoMysql.php");

function filtraEntradaC($dado){
    $dado = trim($dado);
    $dado = stripslashes($dado);
    $dado = htmlspecialchars($dado);
    return $dado;
}   

if($_SERVER["REQUEST_METHOD"] == 'POST'){
    $msgErro = '';
    $nome = $email = $motivo = $mensagem = "";


    $nome = filtraEntradaC($_POST["nome"]);
    $email = filtraEntradaC($_POST["email"]);
    $motivo = filtraEntradaC($_POST["motivo"]);
    $mensagem = filtraEntradaC($_POST["mensagem"]);

    try{


        $sql = "
            INSERT INTO clinicamedica.contato(Id, Nome, Email, Motivo, Mensagem)
            values (null, ? , ? , ? , ?);
        ";

        $stmt = $conn->prepare($sql);

        $stmt->bind_param("ssss", $nome , $email , $motivo , $mensagem);

        if (! $stmt->execute())
            throw new Exception("Erro ao realizar o contato: " . $conn->error);


        $formProcSucesso = true;
        } catch (Exception $e){
            $msgErro = $e->getMessage();
        }
}
?>

When I submit the form of this other page it accuses that login and password of the validaLogin page are not defined.