How to duplicate category name - php

Question

I want to make a input box where first check duplicate category. If it find a duplicate category then it return false but if it don't find duplicate then insert new category name into database.
It check duplicate properly and insert category properly but show this error:
Catchable fatal error: Object of class mysqli_result could not be converted to
string in C:\wamp\www\ecommerce\class\category.php on line 23
Call Stack
# Time Memory Function Location
1 0.0006 137488 {main}() ..\catadd.php:0
2 0.0146 176512 Category->insertCat() ..\catadd.php:15
Here is the method that causes the error:
public function insertCat($catName)
{
$catName = $this->fm->validation($catName);
$catName = mysqli_real_escape_string($this->db->link, $catName);
if(empty($catName)){
$msg = 'Cat name can not empty';
return $msg;
}else{
$dcatName = "select * from tbl_category where catName='$catName'";
$rowCount = $this->db->select($dcatName);
$catRow = mysqli_num_rows($rowCount);
if( $catRow > 0 ){ /* <---- Line 23 ----- */
echo 'Cat Name already Exist';
}else{
$query = "INSERT INTO tbl_category (catName) VALUES ('$catName')";
$catResult= $this->db->insert($query);
if($catResult){
$msg = 'Cat name Updated';
return $msg;
return $msg;
}else{
$msg = 'Not updated';
return $msg;
}
}
}
}
The select method looks like:
// Select or Read data
public function select($query){
$result = $this->link->query($query) or die($this->link->error.__LINE__);
if($result->num_rows > 0)
{
return $result;
}
else
{
return false;
}
}
On compilation, I got this warning:
Warning: mysqli_num_rows() expects parameter 1 to be mysqli_result, boolean given in C:\wamp\www\ecommerce\class\category.php on line 22 ( $catRow = mysqli_num_rows($rowCount); is line 22)

Answer 1

Considering your select method looks like this:
public function select($query)
{
$result = $this->link->query($query) or die($this->link->error.__LINE__);
if($result->num_rows > 0){
return $result;
} else {
return false;
}
}
...this method already checks number of rows so this row:
$catRow = mysqli_num_rows($rowCount);
...is not needed, furthermore, causes an error if the select() method returns no rows, it returns false which will produce the error when you try to reference a method from a false return. You should be able to just do:
# This will either return the resource or false so you don't need
# to count rows
$rowCount = $this->db->select($dcatName);
if($rowCount) {
EDIT:
One point I should make is that you should probably modify your select() method (and any other query methods you have) to accept an array as a second parameter. That second array should let the method know that you need to bind_param so you can use that feature. This may be an SQL Injection vulnerability:
$dcatName = "select * from tbl_category where catName='$catName'";