A Symfony2 Service & Doctrine entity combo for persisting variables and configuration to the database. Inspired heavily by Drupal's variable_get() and variable_set() functions, which can be found here: https://api.drupal.org/api/drupal/includes!bootstrap.inc/function/variable_set/7 .

Variable.php

<?php
namespace Your\ExampleBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;

/**
 * @ORM\Entity
 * @UniqueEntity("name")
 */
class Variable
{
    /**
     * @ORM\Id
     * @ORM\Column(type="integer")
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=32)
     */
    private $name;

    /**
     * @ORM\Column(type="object", nullable=true)
     */
    private $value;

    public function getId()
    {
        return $this->id;
    }

    public function getName()
    {
        return $this->name;
    }

    public function setName($name)
    {
        $this->name = $name;
        return $this;
    }

    public function getValue()
    {
        return $this->value;
    }

    public function setValue($value)
    {
        $this->value = $value;
        return $this;
    }
}

VariablesService.php

<?php
namespace Your\ExampleBundle\Service;

use Your\ExampleBundle\Entity\Variable;
use Doctrine\ORM\EntityManager;

/**
 * A Symfony2 Service for persisting variables and configuration to the database as an entity.
 * Service definition:
 *   variables:
 *       class: Your\ExampleBundle\Service\VariablesService
 *       arguments: [@doctrine.orm.entity_manager]
 *
 * @author Kalman Olah <hello _at_ kalmanolah _dot_ net>
 */
class VariablesService {

    private $em;

    /**
     * Constructs the Service
     * @param EntityManager $em The Doctrine EntityManager
     */
    public function __construct(EntityManager $em) {
        $this->em = $em;
    }

    /**
     * Loads a Variable
     * @param  string $name    Name of the Variable to load
     * @param  mixed  $default Default value to return if the Variable is not found
     * @return Variable|mixed  The Variable object, or the default value
     */
    public function load($name, $default = null)
    {
        $variable = $this->em->getRepository('YourExampleBundle:Variable')->findOneByName($name);

        return $variable ? $variable : $default;
    }

    /**
     * Removes a Variable
     * @param  string $name Name of the Variable to remove
     */
    public function remove($name)
    {
        $variable = $this->load($name);

        if ($variable) {
            $this->em->remove($variable);
            $this->em->flush();
        }
    }

    /**
     * Sets the value of a Variable
     * @param string $name  Name of the Variable whose value to set; if this Variable does not exist it will be created
     * @param mixed  $value Value to give the Variable: this can be any object that can be saved into a Doctrine ORM Object-type field
     */
    public function set($name, $value = null)
    {
        if ($value == null) {
            $this->remove($name);

            return;
        }

        $variable = $this->load($name);
        if (!$variable) {
            $variable = new Variable();
            $variable->setName($name);
        }

        $variable->setValue($value);

        $this->em->persist($variable);
        $this->em->flush();
    }

    /**
     * Gets the value of a Variable
     * @param  string $name    Name of the Variable whose value to get
     * @param  mixed  $default Default value to return if the Variable is not found
     * @return mixed           The value of the Variable object, or the default value
     */
    public function get($name, $default = null)
    {
        $variable = $this->load($name);

        return $variable ? $variable->getValue() : $default;
    }
}