Question

The second echo below throws the error “Trying to get property of non-object?” The first echo prints fine.

$sql = "SELECT id
        FROM files
        WHERE url = '$url'";

$result = $this->mysqli->query($sql);

echo "companyId: " . $result->fetch_object()->id;
echo "\ncompanyId: " . $result->fetch_object()->id;

I’ve doubled up the echo for simplicity of demonstrating this error. I’m actually trying to check if $result->fetch_object()->id is set and then do something with the value if it is. I can’t get that to work correctly because the second time i use it, it throws the error “trying to get property of non-object.”

if(isset($result->fetch_object()->id))
    echo $result->fetch_object()->id;

Answer 1

The mysqli-resultsets works with cursors. This means, if you call fetch_object() the object is fetched (of course), the cursor moves on and now the previously retrieved object not present in the resultset anymore. Retrieve the object into a variable and interact with that, instead of calling fetch_object() multiple times.

$o = $result->fetch_object();