如何通过ID查询数据库中的所有条目？

Question

I was following this tutorial on Udemy about building login form. Everything went well.

Now I'm trying to reuse the code. The problem I'm having is when I'm trying to query all entries from a database in order to get a total number of websites. Could you please advise?

Here is my count function (this is where I'm having issues in obtaining a total number of entries to the database for pagination):

function get_all_websites(){

        $all = array();

        $db = DB::getInstance();
        $all = $db->query("SELECT * FROM website");

        if(!$all->count()){
            echo 'No Websites available. Please check back later.';
        } else {
            foreach($all->results() as $all){
                $all->id = $all;
            }
        }

        return $all;

    }

    function get_websites_count(){

        return count(get_all_websites());

    }

if I use this I get all ID's listed.

function get_all_websites(){

    $all = array();

    $db = DB::getInstance();
    $all = $db->query("SELECT * FROM website");

    if(!$all->count()){
        echo 'No Websites available. Please check back later.';
    } else {
        foreach($all->results() as $all){
            echo $all->id;
        }
    }

}

Database class.

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;

            // Check if query has been prepared properly

            if($this->_query = $this->_pdo->prepare($sql)){

                $x = 1;
                if(count($params)){
                    foreach($params as $param){
                        $this->_query->bindValue($x, $param);
                        $x++;
                    }
                }

            // If the query has been prepared successfuly, store the result
                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;
        }

        // QUERYING DATA FROM DATABASE
        public function get($table, $where){
            return $this->action('SELECT *', $table, $where);
        }

        // DELETING DATA FROM DATABASE
        public function delete($table, $where){
            return $this->action('DELETE', $table, $where);
        }

        // INSERTING DATA INTO DATABASE
        public function insert($table, $fields = array()){
                $keys = array_keys($fields);
                $values = '';
                $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 results(){
            return $this->_results;
        }

        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 first(){
            return $this->results()[0];
        }

        public function error(){
            return $this->_error;
        }

        public function count(){
            return $this->_count;
        }

    }

Answer 1

This part doesn't seem right:

    } else {
        foreach($all->results() as $all){
            $all->id = $all;
        }
    }
    return $all;

but I'm not exactly sure what you want.

We could append each id to an array called $allWebsiteIds:

    } else {
        foreach($all->results() as $all){
            $allWebsiteIds[] = $all->id;
        }
    }
    return $allWebsiteIds;

That might give you what you want.

Answer 2

SQL provides built-in support for counting rows in a table.

SELECT COUNT(*) FROM ...

This is highly optimizable and avoids loading every row into PHP's memory.

Additionally, pay close attention to the construct of your loops; specifically what it means to say:

foreach($foo as $foo)

As part of your study, you should be able to say why that expression is almost never the intended one.

There is a broader rule: Never mutate that which you are iterating over.

Answer 3

Why not use the select to count the rows?

SELECT COUNT(1) FROM website;