无法在mysql插入/更新函数上使用try catch

I have three functions (insert-> for inserting data to database, update-> for updating data and save->it uses try catch)

function save($record,$pk)
{
    try{        
        $this->insert($record);      
    }
    catch(Exception $e)
    {
        $this->update($record,$pk);
    }
}

function insert($record) {
    global $pdo;
    $keys = array_keys($record);

    $values = implode(', ', $keys);
    $valuesWithColon = implode(', :', $keys);

    $query = 'INSERT INTO ' . $this->table . ' (' . $values . ') VALUES (:' . $valuesWithColon . ')';

    $stmt = $pdo->prepare($query);

    $stmt->execute($record);
}

function update($record,$pk)
{
    global $pdo;
    $parameters=[];
    foreach ($record as $key => $value) {
        $parameters[]=$key .'= :'. $key;

    }

    $list=implode(', ',$parameters);
    $query="UPDATE $this->table SET $list WHERE $pk=:pk";
    $record['pk']=$record[$pk];
    $stmt=$pdo->prepare($query);


    $stmt->execute($record);

}

the insert and update function works correctly. I want to use the save function to insert the data if not exists and replace the data if same PK exists.

My code to insert is:

if(isset($_POST['save'])){
    unset($_POST['save']);
    $department->save($_POST,'id');
}

The problem is: if there is no duplicate value, it inserts into the database. But if there is duplicate value(PK), it doesn't update into the database.

My array contains

Array
(
    [id] => 1
    [title] =>test
    [description] =>description    
)

It shows blank when i try to update via form.

P.S: If I replace "save" with "update" then it is updated in the database. But try catch of "save" is not working