php switching to mysqli: num_rows issue - php

Question

I recently started updating some code to MySQL improved extension, and have been successful up until this point:
// old code - works
$result = mysql_query($sql);
if(mysql_num_rows($result) == 1){
$row = mysql_fetch_array($result);
echo $row['data'];
}
// new code - doesn't work
$result = $mysqli->query($sql) or trigger_error($mysqli->error." [$sql]");
if($result->num_rows == 1) {
$row = $result->fetch_array();
echo $row['data'];
}
As shown I am trying to use the object oriented style.
I get no mysqli error, and vardump says no data... but there definitely is data in the db table.

Answer 1

Try this:
<?php
// procedural style
$host = "host";
$user = "user";
$password = "password";
$database = "db";
$link = mysqli_connect($host, $user, $password, $database);
IF(!$link){
echo ('unable to connect to database');
}
ELSE {
$sql = "SELECT * FROM data_table LIMIT 1";
$result = mysqli_query($link,$sql);
if(mysqli_num_rows($result) == 1){
$row = mysqli_fetch_array($result, MYSQLI_BOTH);
echo $row['data'];
}
}
mysqli_close($link);
// OOP style
$mysqli = new mysqli($host,$user, $password, $database);
$sql = "SELECT * FROM data_table LIMIT 1";
$result = $mysqli->query($sql) or trigger_error($mysqli->error." [$sql]"); /* I have added the suggestion from Your Common Sence */
if($result->num_rows == 1) {
$row = $result->fetch_array();
echo $row['data'];
}
$mysqli->close() ;
// In the OOP style if you want more than one row. Or if you query contains more rows.
$mysqli = new mysqli($host,$user, $password, $database);
$sql = "SELECT * FROM data_table";
$result = $mysqli->query($sql) or trigger_error($mysqli->error." [$sql]"); /* I have added the suggestion from Your Common Sence */
while($row = $result->fetch_array()) {
echo $row['data']."<br>";
}
$mysqli->close() ;
?>

Answer 2

As it was said, you're not checking for the errors.
Run all your queries this way
$result = $mysqli->query($sql) or trigger_error($mysqli->error." [$sql]");
if no errors displayed and var dumps are saying no data - then the answer is simple: your query returned no data. Check query and data in the table.

Answer 3

In PHP v 5.2 mysqli::num_rows is not set before fetching data rows from the query result:
$mysqli = new mysqli($host,$user, $password, $database);
if ($mysqli->connect_errno) {
trigger_error(sprintf(
'Cannot connect to database. Error %s (%s)',
$mysqli->connect_error,
$mysqli->connect_errno
));
}
$sql = "SELECT * FROM data_table";
$result = $mysqli->query($sql);
// a SELECT query will generate a mysqli_result
if ($result instanceof mysqli_result) {
$rows = array();
while($row = $result->fetch_assoc()) {
$rows[] = $row;
}
$num_rows = $result->num_rows; // or just count($rows);
$result->close();
// do something with $rows and $num_rows
} else {
//$result will be a boolean
}
$mysqli->close() ;