Fatal error: Uncaught Error: Call to a member function select() on null

Question

I am kinda new to OOP in php and I am facing this problem every time in the model but I can't find the error causing this.

I get an error saying: Fatal error: Uncaught Error: Call to a member function select() on null in my model in the getCategories function (See below code).

<?php

class model_additem extends model{
    public function __construct(){
        DB::setConnection(DB_ADMIN,DB_ADMIN_PASS);
    }

    public function insertItem($picName,$n,$d,$p,$ui,$ic,$pt,$pd="good"){
        $data = ["pic_name"=>$picName,"pic_desc"=>$pd,"pic_type"=>$pt];
        $img = parent::$db->saveTo("pictures")->setData($data)->execute();

        if($img){
            $imgId = parent::$db->lastInsertId();

            $data = ["name"=>$n,"description"=>$d,"price"=>$p,"image_id"=>$imgId,"owner_id"=>$ui,"category_id"=>$ic];
            $prod = parent::$db->saveTo("products")->setData($data)->execute();
            return $prod;
        }
        return false;
    }

    public function getCategories(){
        $data = parent::$db->select()->from('category')->fetch('all');
        if($data) return $data;
        return false;
    }


}

And here is my CONTROLLER file:

<?php

class controller_additem extends controller{
    public function __construct(){
        Load::view("admin".DS."header");
        Load::view('additem/additem');
        Load::view("admin".DS."footer");
        require_once 'CheckAdmin.php'; // Check if the user is admin to enter page + more.


    }

    public function index(){
        $item = $this->model("additem");
        if(isset($_POST["addItem"])){
            $iName = filter_input(INPUT_POST,"iName",FILTER_SANITIZE_MAGIC_QUOTES);
            $iDesc = filter_input(INPUT_POST,"iDesc",FILTER_SANITIZE_MAGIC_QUOTES);
            $iPrice = filter_input(INPUT_POST,"iPrice",FILTER_SANITIZE_NUMBER_FLOAT);
            $iCat = filter_input(INPUT_POST,"category",FILTER_SANITIZE_NUMBER_INT);
            $iPic = $_FILES["iPicture"];

            $extention = explode(".",$iPic["name"]);
            $ext = end($extention);
            //pre($iPic);
            //validation
            //if($iPic["size"]> 2000000){}
            $picName = $iName.time().'.'.$ext;
            if(move_uploaded_file($iPic["tmp_name"],ROOT . "public/images/" . $picName)){
                $userId = Session::get("userId");

                $result = $item->insertItem($picName,$iName,$iDesc,$iPrice,$userId,$iCat,$ext);
                if($result){
                    Session::set("result","Item has been inserted successfully");
                }else{
                    Session::set("result","Error occured");
                }

            }
        }
        $cats = $item->getCategories();
        $uName = Session::get("userData")["name"];
        Load::view("additem/additem",$cats);
    }
}

I also have a db class in my engine file that handles functions related to database and the select function is in there:

class db{
    private static $db = null;
    private $sql = "";
    private $save_type;
    private $binded = array();
    private $query = '';
    private $last_insert_id;

    public function __construct(){
        if(self::$db == null){
            $user = DB_GUEST;
            $pass = DB_GUEST_PASS;
            if(Session::found("user_priv") == 'no'){
                $user = DB_USER;
                $pass = DB_USER_PASS;
            }
            if(Session::found("user_priv") == 'yes'){
                $user = DB_ADMIN;
                $pass = DB_ADMIN_PASS;
            }
            self::setConnection($user,$pass);
        }
    }

    public static function setConnection($user,$pass,$dbname=DB_NAME){
        try{
            self::$db = new PDO("mysql:host=localhost;dbname=$dbname",$user,$pass);
            self::$db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE,PDO::FETCH_ASSOC);
            self::$db->setAttribute(PDO::ATTR_ERRMODE,PDO::ERRMODE_EXCEPTION);
            self::$db->exec("SET NAMES utf8");
        }catch(PDOException $e){
            die($e->getMessage());
        }
    }

    public static function getDb(){
        if(self::$db == null){
            $user = DB_GUEST;
            $pass = DB_GUEST_PASS;
            if(Session::found("userId")){
                $user = DB_USER;
                $pass = DB_USER_PASS;
            }
            if(Session::found("admin")){
                $user = DB_ADMIN;
                $pass = DB_ADMIN_PASS;
            }
            self::setConnection($user,$pass);
        }
        return self::$db;
    }

    //SELECT [name,pass,email]
    public function select(array $select=[]){
        $sql = "SELECT ";
        if(empty($select)){
            $sql .= "*";
        }else{
            filter_array($select);
            $select = implode(",",$select);
            $sql .= string($select);
        }
        $this->sql = $sql;

        return $this;
    }

    //FROM
    public function from($tbl){
        $this->sql .= " FROM " . string($tbl);
        return $this;
    }

    //WHERE
    public function where(array $where){
        //filter_array($where);
        $sql = " WHERE ";
        foreach($where as $key => $val){
            $sql .= $key . " LIKE '".$val."' AND ";
        }

        $this->sql .= rtrim($sql," AND ");
        return $this;
    }

    //JOIN
    public function join(array $tbl,$type="LEFT JOIN"){
        $sql = " ".strtoupper($type)." ";
        $sql .= implode(",",$tbl);

        $this->sql .= $sql;
        return $this;
    }

    //ON
    public function on($cond1,$cond2){
        $sql = " ON ";
        $sql .= string($cond1) . " = " . string($cond2);

        $this->sql .= $sql;
        return $this;
    }

    //ORDER BY
    public function order_by($order_by, $order_type="ASC"){
        $sql = " ORDER BY ";
        $sql .= string($order_by)." ".strtoupper(string($order_type));

        $this->sql .= $sql;
        return $this;
    }

    //LIMIT
    public function limit($limit){
        $this->sql .= " LIMIT " . int($limit);
        return $this;
    }

    //FETCH
    public function fetch($fetch_type=""){
        $fetch = "fetch";
        if($fetch_type){
            $fetch = "fetchAll";
        }

        try{
            $query = self::$db->query($this->sql);
            $this->reset();
            return $query->$fetch();
        }catch(PDOException $e){
            die($e->getMessage());
        }
    }

    //saveTo
    public function saveTo($tbl,$type="insert"){
        $tbl = string($tbl);
        $this->save_type = strtolower(string($type));

        if($this->save_type == "update"){
            $sql = "UPDATE ";
        }elseif($this->save_type == "replace"){
            $sql = "REPLACE INTO ";
        }else{
            $sql = "INSERT INTO ";
        }

        $sql .= $tbl . " SET ";
        $this->sql = $sql;
        return $this;
    }

    //SET DATA
    public function setData(array $data,$filter="string"){
        $filter = string($filter);

        foreach($data as $colomn => $value){
            $colomn = string($colomn);
            $value = $filter($value);
            $this->binded[$colomn] = $value;
            $this->sql .= $colomn . "=:" . $colomn . ",";
        }
        //pre($this->binded);
        $this->sql = rtrim($this->sql,",");
        return $this;
    }

    //execute
    public function execute(){
        try{
            $this->query = self::$db->prepare($this->sql);
            if($this->binded){
                foreach($this->binded as $colomn => $value){
                    $this->bind($colomn,$value);
                }
            }
            $result = $this->query->execute();

            if($this->save_type == 'insert'){
                $this->last_insert_id = self::$db->lastInsertId();
            }
            $this->reset();
            return $result;

        }catch(PDOException $e){
            die($e->getMessage());
        }
    }

    //BIND
    private function bind($placeholder,$value,$filter="string",$bind_type="bindValue"){
        return $this->query->$bind_type(":".$placeholder,$filter($value),PDO::PARAM_STR);
    }

    public function lastInsertId(){
        return $this->last_insert_id;
    }

    //DELETE
    public function delete($tbl,$col=false){
        $this->sql = "DELETE ";
        if($col){
            $this->sql .= string($col)." ";
        }
        $this->sql .= "FROM " . string($tbl);
        return $this;
    }

    //TRUNCATE
    public function truncate($tbl){
        $this->sql = 'TRUNCATE ' . string($tbl);
        return $this;
    }

    //View Query
    public function viewQ(){
        echo $this->sql;
    }

    //RESET
    private function reset(){
        $this->sql = "";
        $this->save_type = "";
        $this->query = "";
        $this->binded = array();
    }
}

The thing is that if you look in the model at the saveTo function, it appears to work. However, select doesn't nor the functions that comes after it.

Please help me, I tried to search for this error but couldn't find the solution for my particular problem.

Any help is highly appreciated! Thanks in advance.

EDIT: Thanks everybody for your help! I figured it out. There was a mistake in the model class so the there wasn't connection with the db.

Answer 1

It appears that $db is not defined in the parent class. Which is model. Are you sure you initialized it?

If you initialized it in the parent constructor (in the class model) you need to call it explicitly in your current constructor (in the class model_addItem). PHP will not do that automatically.

Answer 2

The error suggests that select() is called on a null object. Do a var_dump() on your parent::$db and make sure that the object is not actually empty.