Function validate users registration

Question

I’m starting in OO in php, and with the function below I’m trying to check if the name coming from the form is equal to some value coming from my user table before making Insert in the table. I wish someone could shed some light since none of the attempts have worked so far and this is as close as I can get.

    public function validarDadosUsuario($validaNome) {
        require('conexao.php');
        $sql = "SELECT * FROM usuario";
        $result = $conn->query($sql);
        $dados = $result->fetchAll(PDO::FETCH_ASSOC);

        foreach ($dados as $row) {

            foreach ($row as $indice => $value) {

                if($row[$indice] == $validaNome) {
                    echo 'Nomes iguais';
                    $this->$validaNome = true;
                    break;

                } else {
                    echo 'Nomes diferentes';
                    $this->validaNome = false;
                }
            }

        }

        return $validaNome;
    }

$usuario = new Usuario($_POST['add_name'], $_POST['add_email'], $_POST['add_type'], $_POST['add_password']);

$user->validatedUsuario($_POST['add_name']);

Answer 1

If the function is only to validate the Name, you could already select in the table using the value passed by $_POST['add_nome'] and from that it is only you do the treatment using if the select returns True or False.

Kind of like this:

$usuario = new Usuario($_POST['add_nome'], $_POST['add_email'], $_POST['add_tipo'], $_POST['add_senha']);
$usuario->validarDadosUsuario($_POST['add_nome']);

public function validarDadosUsuario($validaNome) {
        require('conexao.php');
        $sql = "SELECT * FROM usuario WHERE nomeDacoluna = '$validaNome'"; //A condição WHERE pra buscar os dados na tabela
        $result = $conn->query($sql);

        //Retorna o número de linhas do resultado do select
        $retorno = $result->rowCount();

        //Verificando se o select retornou algum resultado;
        if($retorno != 0):
            echo 'Já existe esse Nome (Nome Repetido)';
        exit;
        else:
            echo 'Não Existe esse Nome (Nome Novo)';
        exit;
        endif;
    }