Update form to work when deploying Ajax

This is Ajax that I want to implement. When the form is submitted, it displays a GIF to show that it is loading, and then depending on the result, an alert appears with a message written by json_encode , and some.

$("#form").submit(function(e) {
    e.preventDefault();

    $("#loading").fadeIn();

    $.ajax({
        type: "POST",
        url: "Operations.php",
        data: $("#form").serialize(),
        dataType: "json",
        success: function(data) {
            $("#loading").hide();
            showAlert("result-success", data.msg);
        },
        error: function(jqXHR, textStatus, errorThrown) {
            $("#loading").hide();
            showAlert("result-error", "Ocorreu um erro ao continuar");
        }
    });
});

Below, the Operations.php file receives POST the class name and the id through two hidden , executes an operation depending on the form and finally sends a result and a message to JSON, which will be displayed by the alert created by Ajax

<?php

$class = filter_input(INPUT_POST, "class");
$id = filter_input(INPUT_POST, "id");

@require_once "../../php/Connection.php";
@require_once "../../php/ServiceDatabase.php";
@require_once "../../php/" . $class . ".php";

$Operation = new ServiceDatabase($connection, new $class);

switch ($_REQUEST["submit"]) {
    case "insert":
        $Operation->setPostVariables();

        if ($Operation->insert()) {
            $res = "success";
            $msg = "Dados inseridos com sucesso";
        }

        break;
    case "update":
        $Operation->setPostVariables();

        if ($Operation->update($id)) {
            $res = "success";
            $msg = "Dados atualizados com sucesso";
        }

        break;
    case "delete":
        if ($Operation->delete($id)) {
            $res = "success";
            $msg = "Dados apagados com sucesso";
        }

        break;
}

echo json_encode(array(
    "res" => $res,
    "msg" => $msg
));

Finally, the form. When submitted, it sends the values assigned to hidden , and also the value of button , which will cause an action to be executed.

<?php
session_start();

$class = ucfirst(filter_input(INPUT_GET, "t"));
$id = filter_input(INPUT_GET, "i");

require_once "../../php/" . $class . ".php";

$Table = new ServiceDatabase($connection, new $class);
?>

<form id="form" class="center-block" action="Operations.php" method="post">
    <h3>Alterar - <small><?php echo $class ?></small></h3>

    <input type="hidden" value="<?php echo $class ?>" name="class"/>
    <input type="hidden" value="<?php echo $id ?>" name="id"/>

    <?php echo $Table->generateAdminTables($id); ?>

    <button type="submit" name="submit" value="update" class="btn btn-primary btn-update">Atualizar</button>
    <button type="submit" name="submit" value="delete" class="btn btn-danger btn-delete fright">Apagar</button>
</form>

The Problem

Ajax runs and displays the alert when it falls in success , but does not display any messages. It is undefined , and in addition, no operation of the second file is executed, although it shows success. If I simply comment on Ajax, everything works fine.

Issue # 1

Upon request, the return of data is Object { res: null, msg: null } . Another detail I forgot to comment on is that by removing Ajax and clicking the button to refresh the data, when it redirects to the Operations.php file to perform some operation, you can see printed on the screen information json_encode .