试图在php中获取非对象的属性

Question

I'm getting an error

"Trying to get property of non object" on : if ($result4->num_rows > 0) .

Why this is occurring?And how to prevent it happening again. I'm just starting with php... Can it be solved? Thank you in advance.

if (isset($_POST['submit'])) 
{
    if (isset($_POST['ID'])) {
    $sql = "SHOW COLUMNS FROM Employees";
    $result = mysqli_query($con,$sql);
     while($row = mysqli_fetch_array($result)){
                $tempname = $row['Field'];

                // Changes Function
                $sqlCheck = "SELECT * FROM Employees WHERE ID='".$_GET["id"]."' AND (".$row['Field']." NOT LIKE '".$_POST[$tempname]."')";
                $result3 = $con->query($sqlCheck);
                if ($result3->num_rows > 0) {
                // output data of each row
                while($row3 = $result3->fetch_assoc()) {
                    $sql3 = "INSERT INTO `Changes` (`Table`, `ID`, `Attribute`, `DateChanged`, `HRUser`, `OldValue`, `NewValue`)

VALUES ('Employees', '".$_GET["id"]."', '".$row["Field"]."', '".date("d/m/Y h:i:sa")."', '$login_session', '$row3[$tempname]', '$_POST[$tempname]')";
                    if ($con->query($sql3) === TRUE) {
                    } else {
                    echo "Error: " . $sql3 . "<br>" . $con->error;
                    }
                }
                }

Answer 1

Do not mix both mysqli fuctions and OOP Concept Try this Code

if (isset($_POST['submit'])) 
{
    if (isset($_POST['AFNumber'])) {
    $sql = "SHOW COLUMNS FROM Employees";
    $result = mysqli_query($con,$sql);
     while($row = mysqli_fetch_array($result)){
                $tempname = $row['Field'];

                // Changes Function
                $sqlCheck = "SELECT * FROM Employees WHERE AFNumber='".$_GET["af"]."' AND (".$row['Field']." NOT LIKE '".$_POST[$tempname]."')";
                $result3 = mysqli_query($con,$sqlCheck);
                if (mysqli_num_rows($result3) > 0) {
                // output data of each row
                while($row3 = mysqli_fetch_array($result3)) {
                    $sql3 = "INSERT INTO `Changes` (`Table`, `AFNumber`, `Attribute`, `DateChanged`, `HRUser`, `OldValue`, `NewValue`)

VALUES ('Employees', '".$_GET["af"]."', '".$row["Field"]."', '".date("d/m/Y h:i:sa")."', '$login_session', '$row3[$tempname]', '$_POST[$tempname]')";
                    if (mysqli_query($con,$sql3) === TRUE) {
                    } else {
                    echo "Error: " . $sql3 . "<br>" . mysqli_error($con);
                    }
                }
                }
                //End Changes Function


                $sql2 = "UPDATE Employees SET ".$row['Field']."= '$_POST[$tempname]' WHERE AFNumber='".$_GET["af"]."'";
                $result2 = mysqli_query($con,$sql2);
                if (mysqli_query($con,$sql2) === TRUE) {
                } else {
                    echo "Error: " . $sql2 . "<br>" . mysqli_error($con);
                    echo '<script>swal("Error", "Something went wrong '.mysqli_error($con).'", "error");</script>';
                }

}       




    echo '<script>swal("Success", "Changes have been saved", "success");</script>';
} //End If POST Submit True
    else{

     $sql = "SHOW COLUMNS FROM Candidates";
    $result = mysqli_query($con,$sql);
     while($row = mysqli_fetch_array($result)){
                $tempname = $row['Field'];


            // Changes Function
                $sqlCheck = "SELECT * FROM Candidates WHERE CID='".$_GET["cid"]."' AND (".$row['Field']." NOT LIKE '%".$_POST[$tempname]."%')";
                $result4 = mysqli_query($con,$sqlCheck);
                if (mysqli_num_rows($result4) > 0) {
                // output data of each row
                while($row4 = mysqli_fetch_array($result4)) {
                    $sql4 = "INSERT INTO `Changes` (`Table`, `AFNumber`, `Attribute`, `DateChanged`, `HRUser`, `OldValue`, `NewValue`)

VALUES ('Candidates', '".$_GET["cid"]."', '".$row["Field"]."', '".date("d/m/Y h:i:sa")."', '$login_session', '$row4[$tempname]', '$_POST[$tempname]')";
                    if (mysqli_query($con,$sql4) === TRUE) {
                    } else {
                    echo "Error: " . $sql4 . "<br>" . mysqli_error($con);
                    }
                }
                }



    }

    echo '<script>swal("Success", "Changes have been saved", "success");</script>';


    }}