Cron job – running PHP in the background

Background jobs

If you wish to write responsive web applications, you will need to  push some operations in the background. That way you can just register request for some long running task and immediately return to the client.

If you search the web, there are many ways how to achieve this, but not so many implementation are ready to do it in constraint environment of simple web hosting.

My web page is hosted by GoDaddy with so called “Linux hosting with cPanel”. I have PHP and MySql, but not much beside this. GoDaddy luckily allows cron jobs.  We simply register some command as “cron job” to run unattended at specified frequency.

For proof of concept I will need simple php program and run it as cron job.  At each cron job iteration we will insert one record into database table. We just want to proof that php program can run in the background as  cron job.

Create some database and add “tasklog” table.

create table tasklog (
    id int not null auto_increment,
    created datetime,
    primary key (id)
)

Our simple PHP program is :

<?php
try {
    $host = "localhost";
    $dbname = "your_database";
    $user = "your_db_user";
    $pass = "your_password";

    # MySQL with PDO_MYSQL
    $db = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
    $db->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

    $stmt = $db->prepare("INSERT INTO tasklog(`created`) VALUES(NOW())");
    $stmt->execute();
  
    $db = null;
}
catch(PDOException $e) {
    echo $e->getMessage();
}

To test it, just put the “taskrun.php” in your “public_html” folder and navigate to it. If something will go wrong in the program, the settings for exceptions are set to report it to the client. Please test the program until everything not running smoothly.

Register cron job

You can put program file to any folder. If folder is not under “public_html” folder, it will be inaccessible from the public web and that way will be much more secure. We create new “jobs” folder under our root home folder and move “taskrun.php” program there.

In the “cPanel” locate “Advanced” section and select “Cron Jobs”:

2015-10-22 22_42_41-cPanel - MainCreate new job with a one minute frequency as:

/usr/local/bin/php "$HOME/jobs/taskrun.php" > /dev/null 2>&1

To prevent email to be sent for each iteration, we put redirection into the command ( > /dev/null 2>&1 ).

2015-10-22 22_45_26-cPanel - Cron JobsWait a minute and check if there are some records in the “tasklog” table. You will see something like this:

2015-10-23 00_10_00-n1plcpnl0026.prod.ams1.secureserver.net _ localhost _ bisagasamples _ tasklog _

Success !

Of course, this is only proof of concept for running something unattended in the background. But I think there are already some open source job-task runner out there.

 

Doctrine DBAL – working with database

In this article I am going to cover using MySql database in Symfony 2 application.

I will use the simplest possible database access technology PHP offers – PDO,  but in slightly extended form of Doctrine DBAL. So if you want to use Doctrine ORM , this article is not right place to start.

Before we begin

We need some sample data in the database,  so we create a database “dbsamples” with “country” table and import data from this csv file. Because I will not use full Doctrine ORM ,  generating db schema is not an option, I will create database manually.

create table country (
    id int not null auto_increment,
    name char varying(250) not null,
    formal_name	char varying(250),
    legal_type char varying(100),
    legal_sub_type char varying(100),
    sovereignty char varying(100),
    capitol_city char varying(100),
    currency_code char varying(30), 
    currency_name char varying(100),
    telephone_code char varying(100),
    iso2code char varying(2),
    iso3code char varying(3),
    iso3num char varying(3),
    domain_code char varying(20),
    primary key (id),
    key ix_name (name),
    key ix_formal_name (formal_name)
)

You can use phpMyAdmin for that,  it is usually installed by default. If you need true utf8 database, you need to set character set to utf8mb4.

Connecting to the database

Because we use Symfony standard framework, we already have  connection parameters in a configuration file (“parameters.yml”).

# This file is auto-generated during the composer install
parameters:
    database_driver: pdo_mysql
    database_host: 127.0.0.1
    database_port: 3306
    database_name: dbsamples
    database_user: dbuser
    database_password: mypassword
    # [20] PDO::ATTR_EMULATE_PREPARES = false, 
    # [17] PDO::ATTR_STRINGIFY_FETCHES = false
    database_options: {20: 0, 17: 0}

I added one new parameter here, an array of custom driver options (“database_options”). By default all received data to php are stringified, it means you get all data in strings. To receive native data types from the database (int as integer for example), you need to set those options and use prepared statements. But this options will only work if you have luck and your hosting installed and enabled  “mysqlnd” native driver, check your hosting for the driver type.

In the config.yml file, this parameters are mapped to dbal connection  parameters:

# Doctrine Configuration
doctrine:
    dbal:
        driver:   "%database_driver%"
        host:     "%database_host%"
        port:     "%database_port%"
        dbname:   "%database_name%"
        user:     "%database_user%"
        password: "%database_password%"
        charset:  UTF8
        options: "%database_options%"

When we are in the symfony controller file (as in \AppBundle\Controller\DefaultController.php for example), we get connection directly from the container:

$cn = $this->getDoctrine()->getConnection();

or more specific for DBAL connection :

$cn = $this->container->get('doctrine.dbal.default_connection');

but because aquired connections are not pooled (php connections do not support connection pool yet), is actually the same if you create new connection by yourself :

$config = new \Doctrine\DBAL\Configuration();
$connectionParams = array('url'=>'mysql://dbuser:mypassword@localhost/dbsamples' );
$cn = \Doctrine\DBAL\DriverManager::getConnection($connectionParams, $config);

Selecting data

Selecting data in DBAL is easy and intuitive, just use connections executeQuery method. If you use parameters in SQL statement, this will create prepared statement for you and bind parameters automatically. You should always use prepared statements because they are more secure and more efficient as plain text statements.

//create prepared statement and execute it 
$stmt = $cn->executeQuery("SELECT * FROM country WHERE id = :id", array("id"=>157));

But there is even better way, using QueryBuilder object and assembling SQL statement with PHP code.

$stmt = $cn->createQueryBuilder()
        ->select("*")
        ->from("country")
        ->where("id = :id")
        ->setParameters(array("id"=>157))
        ->execute();

Fetch data to types

To get result from a statement, we need to execute one of the “fetch” methods.

$country = $stmt->fetch();

By default we receive each result row as an array, or as array of arrays for multiple records. We can even fetch directly to an instance of an class:

//fetch result to class instance 
$stmt->setFetchMode(\PDO::FETCH_CLASS | \PDO::FETCH_PROPS_LATE, "\Bisaga\Database\Model\Country");
        
/*@var $country \Bisaga\Database\Model\Country  */
$country = $stmt->fetch();

Don’t forget we have all the power of PDO library at our disposal.

With little help from variable type hinting , we get full code completion on received object instance in the IDE:

2015-09-27 11_05_12-Untitled - paint.net 4.0.6Well, that’s of course possible only in case we use same exact names in database and in php class :

<?php

namespace Bisaga\Database\Model;

/**
 * Country table 
 */
class Country {
    /**
     * Row identifier 
     * @var integer auto numbered unique identifier
     */
    public $id;

    /**
     * Country name 
     * @var string country name  
     */
    public $name;
    
    /**
     * Formal country name 
     * @var string 
     */
    public $formal_name;

    /**
     * Country legal type 
     * @var string  
     */
    public $legal_type;
    
    /**
     * Country legal subtype 
     * @var string 
     */
    public $legal_sub_type;

    /**
     * Country sovereignty 
     * @var string  
     */
    public $sovereignty;

    /**
     * Country capitol 
     * @var string 
     */
    public $capitol_city;
    
    /**
     * Currency code 
     * @var string  
     */
    public $currency_code;
    
    /**
     * Country currency name  
     * @var string 
     */
    public $currency_name;

    /**
     * Country telephone code 
     * @var string
     */
    public $telephone_code;
    
    /**
     * Country 2 characters iso code 
     * @var string 
     */
    public $iso2code;

    /**
     * Country 3 characters iso code 
     * @var string 
     */
    public $iso3code;

    /**
     * Country 3 characters numeric iso code 
     * @var string 
     */
    public $iso3num;
    
    /**
     * Country domain name suffix
     * @var string 
     */
    public $domain_code;
    
}

Custom columns mapping

Well, you really need to have a very good reason to select different names for columns in database, but sometimes you are not original owner of database. In that case you could introduce mapping function like this:

 /**
 * Function create instance of target type and fill target properties 
 * 
 * @param object $sourceObject Object instance or array as source 
 * @param string $targetClass Target class name fith full namespace 
 * @param array $mapping  array with mapping names, 
 *                        key represent name of the property in source object, 
 *                        value represent column name in target object 
 * @return any function return object instance of target type 
 */
private function castToClass($sourceObject, $targetClass, $mapping = null)
{
	$target = new $targetClass();
	if (is_array($sourceObject) || is_object($sourceObject)) {
		foreach ($sourceObject as $key => $value) {
			
			if (null === $mapping ) {
				$target->$key = $value;
			}
			elseif ( array_key_exists($key, $mapping) )
			{
				$mapped_name = $mapping[$key];
				$target->$mapped_name = $value; 
			}
		}
	}
	return $target;
}

Prepare sample for mapping

We create new table “currency” in the database  :

create table currency (
    numeric_code int not null,
    currency_code char varying(20) not null,
    primary key (numeric_code),
    key ix_code (currency_code)
)

and write new class “Currency” in php :

<?php

namespace Bisaga\Database\Model;
/*
 * Currency table 
 */
class Currency {
    /**
     * Currency code (840, 978 etc.)
     * @var integer currency numeric value 
     */
    public $id;
    /**
     * Currency code (USD, EUR etc.)
     * @var string currency code 
     */
    public $code;
}

We do not want push to far in this direction, we could start developing a new ORM or something and that is not our intention. We want to retain full power of SQL language in the application, without need to write to much PHP or SQL code manually.

Usage example:
 $stmt = $cn->createQueryBuilder()
                ->select("numeric_code, currency_code")
                ->from("currency")
                ->where("id = :id")
                ->setParameters(array("id"=>852))
                ->execute();
        
 $object = $stmt->fetch();
 /*@var $currency \Bisaga\Database\Model\Currency  */
 $currency = $this->castToClass($object, 
               "\Bisaga\Database\Model\Currency", 
               array("numeric_code" => "id", 
                     "currency_code"=>"code"));

Mapping array contain database columns first (as keys) and class properties second (as values).

Inserting data

Inserting data is straightforward :

$cn->insert("country", (array)$country);
$country->id = $cn->lastInsertId();

Because insert command expect array as second parameter, we simply convert object instance ($country)  to associative array.  After record is inserted, we inspect last inserted value in auto numbered column and return value to the program.

Update data

Update is very similar to insert, except we need to add third parameter to find existing record :

 $cn->update("country", (array)$country, array("id"=>$country->id));

Delete data

And deleting is event simpler:

$cn->delete("country", array("id"=>$country->id));

I didn’t mentioned that all commands are available as query builder methods.

Working with transactions

There is full transaction support directly in php code. We must explicitly start transaction and commit after last database command. In case of errors we need to call rollback on the used connection.

$cn->beginTransaction();
try {
	$cn->insert("country", (array)$country);
	$country->id = $cn->lastInsertId();
	$cn->commit();
} catch (Exception $exc) {
	$cn->rollBack();
	throw $exc;
}

If you think this is little verbose and want to shorten the code, you actually can, just use closure with “transactional” function :

/**
 * @param \Bisaga\Database\Model\Country $country
 */
public function insertWithClosure(\Bisaga\Model\Country $country)
{            
	// use closure form with beginTransaction/commit/rollBack support 
	$this->getConnection()->transactional(function(\Doctrine\DBAL\Connection $cn) use ($country) {
		/* @var $cn Connection */
		$cn->insert("country", (array)$country);
		$country->id = $cn->lastInsertId();
	});
}