Database class for prepared statements in PHP using MySQLi

gistfile1.php

<?php
// Be sure to input YOUR database details below
// Watch the associated videos here: https://www.youtube.com/playlist?list=PLLs69n7Q4dCx5_7ZwnxTymH8X0iRP_2vw

define( 'DB_USER', 'DB USERNAME' );
define( 'DB_PASS', 'DB PASSWORD' );
define( 'DB_NAME', 'DB NAME' );
define( 'DB_HOST', 'localhost' );
define( 'DB_ENCODING', '' );

if ( !class_exists( 'DB' ) ) {
	class DB {
		public function connect() {
			return new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
		}
		public function query($query) {
			$db = $this->connect();
			$result = $db->query($query);
			
			while ( $row = $result->fetch_object() ) {
				$results[] = $row;
			}
			
			return $results;
		}
		public function insert($table, $data, $format) {
			// Check for $table or $data not set
			if ( empty( $table ) || empty( $data ) ) {
				return false;
			}
			
			// Connect to the database
			$db = $this->connect();
			
			// Cast $data and $format to arrays
			$data = (array) $data;
			$format = (array) $format;
			
			// Build format string
			$format = implode('', $format); 
			$format = str_replace('%', '', $format);
			
			list( $fields, $placeholders, $values ) = $this->prep_query($data);
			
			// Prepend $format onto $values
			array_unshift($values, $format); 

			// Prepary our query for binding
			$stmt = $db->prepare("INSERT INTO {$table} ({$fields}) VALUES ({$placeholders})");

			// Dynamically bind values
			call_user_func_array( array( $stmt, 'bind_param'), $this->ref_values($values));
			
			// Execute the query
			$stmt->execute();
			
			// Check for successful insertion
			if ( $stmt->affected_rows ) {
				return true;
			}
			
			return false;
		}
		public function update($table, $data, $format, $where, $where_format) {
			// Check for $table or $data not set
			if ( empty( $table ) || empty( $data ) ) {
				return false;
			}
			
			// Connect to the database
			$db = $this->connect();
			
			// Cast $data and $format to arrays
			$data = (array) $data;
			$format = (array) $format;
			
			// Build format array
			$format = implode('', $format); 
			$format = str_replace('%', '', $format);
			$where_format = implode('', $where_format); 
			$where_format = str_replace('%', '', $where_format);
			$format .= $where_format;
			
			list( $fields, $placeholders, $values ) = $this->prep_query($data, 'update');
			
			//Format where clause
			$where_clause = '';
			$where_values = '';
			$count = 0;
			
			foreach ( $where as $field => $value ) {
				if ( $count > 0 ) {
					$where_clause .= ' AND ';
				}
				
				$where_clause .= $field . '=?';
				$where_values[] = $value;
				
				$count++;
			}

			// Prepend $format onto $values
			array_unshift($values, $format);
			$values = array_merge($values, $where_values);

			// Prepary our query for binding
			$stmt = $db->prepare("UPDATE {$table} SET {$placeholders} WHERE {$where_clause}");
			
			// Dynamically bind values
			call_user_func_array( array( $stmt, 'bind_param'), $this->ref_values($values));
			
			// Execute the query
			$stmt->execute();
			
			// Check for successful insertion
			if ( $stmt->affected_rows ) {
				return true;
			}
			
			return false;
		}
		public function get_results($query) {
			return $this->query($query);
		}
		public function get_row($query) {
			$results = $this->query($query);
			
			return $results[0];
		}
		public function delete($table, $id) {
			// Connect to the database
			$db = $this->connect();
			
			// Prepary our query for binding
			$stmt = $db->prepare("DELETE FROM {$table} WHERE ID = ?");
			
			// Dynamically bind values
			$stmt->bind_param('d', $id);
			
			// Execute the query
			$stmt->execute();
			
			// Check for successful insertion
			if ( $stmt->affected_rows ) {
				return true;
			}
		}
		private function prep_query($data, $type='insert') {
			// Instantiate $fields and $placeholders for looping
			$fields = '';
			$placeholders = '';
			$values = array();
			
			// Loop through $data and build $fields, $placeholders, and $values			
			foreach ( $data as $field => $value ) {
				$fields .= "{$field},";
				$values[] = $value;
				
				if ( $type == 'update') {
					$placeholders .= $field . '=?,';
				} else {
					$placeholders .= '?,';
				}
				
			}
			
			// Normalize $fields and $placeholders for inserting
			$fields = substr($fields, 0, -1);
			$placeholders = substr($placeholders, 0, -1);
			
			return array( $fields, $placeholders, $values );
		}
		private function ref_values($array) {
			$refs = array();

			foreach ($array as $key => $value) {
				$refs[$key] = &$array[$key]; 
			}

			return $refs; 
		}
	}
}

$db = new DB;

//print_r($db->insert('objects', array('post_title'=>'Abstraction Test', 'post_content' => 'Abstraction test content'), array('%s', '%s')));
//print_r($db->update('objects', array('post_title'=>'Abstraction Test Update', 'post_content' => 'Abstraction test update content'), array('%s', '%s'), array('ID'=>28), array('%d')));
//print_r($db->get_results("SELECT * FROM objects"));
//print_r($db->get_row("SELECT * FROM objects"));
//print_r($db->delete('objects', 9));

Hi, know this is old, but this is very useful. Had a question - how would you construct an UPDATE with a more complex WHERE ? This looks like can only update using = operator. Can't use != , or OR etc?

Yes, this is very helpful. I used the insert function but got error in call_user_func_array( array( $stmt, 'bind_param'), $this->ref_values($values)); so i changed this line to $bp = call_user_func_array(array($stmt, "bind_param"), array_merge(array($format), $values));
Now there is no error and insertion also not happening. Any idea about my issue?

Change line 88 from
$where_values = '';
to
$where_values = array();