$wpdb query not working in plugin - wordpress

Question

I'm trying to do a reviews plugin in Wordpress, and one of the thing that my client asked me to do was that a user should be able to rate only one product every 24 horas, so I have to establish a limit between rates.
And I made this function to check if the limit is reached:
function isAllowedToRate(){
global $wpdb;
$currentDate = date('Y-m-d');
$userId = get_current_user_id();
$table_name = $wpdb->prefix .'esvn_reviews';
$isAllowed = $wpdb->get_results(
"
SELECT user_id, fecha_calificacion
FROM {$table_name}
WHERE user_id = {$userId}
AND review_date = {$currentDate}
"
);
if( count( $isAllowed > 0 ) ){
return false;
}else{
return true;
}
}
But every time I try to run it, it returns false, the error that I'm getting from Wordpress is this:
<div id='error'>
<p class='wpdberror'><strong>WordPress database error:</strong> []<br />
<code>
SELECT user_id, fecha_calificacion
FROM wp_esvn_reviews
WHERE user_id = 6
AND fecha_calificacion = 2015-10-30
</code></p>
</div>
If I take the same SQL and run it directly into the database, it works like a charm, but I keep getting this error from Wordpress and the function always returns false.

Answer 1

You need to wrap your date in single quotes.
$isAllowed = $wpdb->get_results(
"
SELECT user_id, fecha_calificacion
FROM {$table_name}
WHERE user_id = {$userId}
AND review_date = '{$currentDate}'
"
);
Alternatively you could use $wpdb->prepare(), which I would consider better form.
$sql = <<<SQL
SELECT user_id, fecha_calificacion
FROM {$table_name}
WHERE
user_id = %d -- this is formatted as a (d)igit
AND review_date = %s -- this is formatted as a (s)tring
SQL;
$isAllowed = $wpdb->get_results($wpdb->prepare($sql, $userId, $currentDate));

Answer 2

I found the error (in case someone needs the information in the future), I was treating $isAllowed as an array, and it was an object, I had to add ARRAY_A to the get_results:
$isAllowed = $wpdb->get_results(
"
SELECT user_id, fecha_calificacion
FROM {$table_name}
WHERE user_id = {$userId}
AND review_date = {$currentDate}
",ARRAY_A /* output as an associative array */
);