How to create mini cms with OOP? - php

Question

Im using OOP and im new with that. I just dont get it...i tryed everything and i just can't make a simple text edit, for ex:
I want to make a form where i can edit text from main page. So for ex i want to edit footer text "copyright by bla bla" i want to edit that by using simple form. It sounds easy but for me with oop...its not that much.
This is example of my register/login system and i tryed to make it similar to this but can't figure it out.
class DB{
private static $_instance = null;
private $_pdo,
$_query,
$_error = false,
$_results,
$_count = 0;
private function __construct(){
try{
$this->_pdo = new PDO('mysql:host=' . Config::get('mysql/host') . ';dbname=' . Config::get('mysql/db'), Config::get('mysql/username'), Config::get('mysql/password'));
} catch(PDOException $e){
die($e->getMessage());
}
}
public static function getInstance(){
if(!isset(self::$_instance)){
self::$_instance = new DB();
}
return self::$_instance;
}
public function query($sql, $params = array()){
$this->_error = false;
if($this->_query = $this->_pdo->prepare($sql)){
$x = 1;
if(count($params)){
foreach($params as $param){
$this->_query->bindValue($x, $param);
$x++;
}
}
if($this->_query->execute()){
$this->_results = $this->_query->fetchAll(PDO::FETCH_OBJ);
$this->_count = $this->_query->rowCount();
} else {
$this->_error = true;
}
}
return $this;
}
public function action($action, $table, $where = array()){
if(count($where) === 3){
$operators = array('=', '>', '<', '>=', '<=');
$field = $where[0];
$operator = $where[1];
$value = $where[2];
if(in_array($operator, $operators)){
$sql = "{$action} FROM {$table} WHERE {$field} {$operator} ?";
if(!$this->query($sql, array($value))->error()){
return $this;
}
}
}
return false;
}
public function get($table, $where){
return $this->action('SELECT *', $table, $where);
}
public function delete($table, $where){
return $this->action('DELETE', $table, $where);
}
public function insert($table, $fields = array()){
$keys = array_keys($fields);
$values = null;
$x = 1;
foreach($fields as $field){
$values .= '?';
if($x < count($fields)){
$values .= ', ';
}
$x++;
}
$sql = "INSERT INTO {$table} (`" . implode('`, `', $keys) . "`) VALUES ({$values})";
if(!$this->query($sql, $fields)->error()){
return true;
}
return false;
}
public function update($table, $id, $fields){
$set = '';
$x = 1;
foreach($fields as $name => $value){
$set .= "{$name} = ?";
if($x < count($fields)){
$set .= ', ';
}
$x++;
}
$sql = "UPDATE {$table} SET {$set} WHERE id = {$id}";
if(!$this->query($sql, $fields)->error()){
return true;
}
return false;
}
public function results(){
return $this->_results;
}
public function first(){
return $this->results()[0];
}
public function error(){
return $this->_error;
}
public function count(){
return $this->_count;
}
}