Advanced field value conversion using custom mapping types

Section author: Jan Sorgalla <jsorgalla@googlemail.com>

When creating entities, you sometimes have the need to transform field values before they are saved to the database. In Doctrine you can use Custom Mapping Types to solve this (see: Custom Mapping Types).

There are several ways to achieve this: converting the value inside the Type class, converting the value on the database-level or a combination of both.

This article describes the third way by implementing the MySQL specific column type Point.

The Point type is part of the Spatial extension of MySQL and enables you to store a single location in a coordinate space by using x and y coordinates. You can use the Point type to store a longitude/latitude pair to represent a geographic location.

The entity

We create a simple entity whith a field $point which holds a value object Point representing the latitude and longitude of the position.

The entity class:

<?php

namespace Geo\Entity;

/**
 * @Entity
 */
class Location
{
    /**
     * @Column(type="point")
     *
     * @var \Geo\ValueObject\Point
     */
    private $point;

    /**
     * @Column(type="string")
     *
     * @var string
     */
    private $address;

    /**
     * @param \Geo\ValueObject\Point $point
     */
    public function setPoint(\Geo\ValueObject\Point $point)
    {
        $this->point = $point;
    }

    /**
     * @return \Geo\ValueObject\Point
     */
    public function getPoint()
    {
        return $this->point;
    }

    /**
     * @param string $address
     */
    public function setAddress($address)
    {
        $this->address = $address;
    }

    /**
     * @return string
     */
    public function getAddress()
    {
        return $this->address;
    }
}

We use the custom type point in the @Column docblock annotation of the $point field. We will create this custom mapping type in the next chapter.

The point class:

<?php

namespace Geo\ValueObject;

class Point
{

    /**
     * @param float $latitude
     * @param float $longitude
     */
    public function __construct($latitude, $longitude)
    {
        $this->latitude  = $latitude;
        $this->longitude = $longitude;
    }

    /**
     * @return float
     */
    public function getLatitude()
    {
        return $this->latitude;
    }

    /**
     * @return float
     */
    public function getLongitude()
    {
        return $this->longitude;
    }
}

The mapping type

Now we’re going to create the point type and implement all required methods.

<?php

namespace Geo\Types;

use Doctrine\DBAL\Types\Type;
use Doctrine\DBAL\Platforms\AbstractPlatform;

use Geo\ValueObject\Point;

class PointType extends Type
{
    const POINT = 'point';

    public function getName()
    {
        return self::POINT;
    }

    public function getSqlDeclaration(array $fieldDeclaration, AbstractPlatform $platform)
    {
        return 'POINT';
    }

    public function convertToPHPValue($value, AbstractPlatform $platform)
    {
        list($longitude, $latitude) = sscanf($value, 'POINT(%f %f)');

        return new Point($latitude, $longitude);
    }

    public function convertToDatabaseValue($value, AbstractPlatform $platform)
    {
        if ($value instanceof Point) {
            $value = sprintf('POINT(%F %F)', $value->getLongitude(), $value->getLatitude());
        }

        return $value;
    }

    public function canRequireSQLConversion()
    {
        return true;
    }

    public function convertToPHPValueSQL($sqlExpr, AbstractPlatform $platform)
    {
        return sprintf('AsText(%s)', $sqlExpr);
    }

    public function convertToDatabaseValueSQL($sqlExpr, AbstractPlatform $platform)
    {
        return sprintf('PointFromText(%s)', $sqlExpr);
    }
}

We do a 2-step conversion here. In the first step, we convert the Point object into a string representation before saving to the database (in the convertToDatabaseValue method) and back into an object after fetching the value from the database (in the convertToPHPValue method).

The format of the string representation format is called Well-known text (WKT). The advantage of this format is, that it is both human readable and parsable by MySQL.

Internally, MySQL stores geometry values in a binary format that is not identical to the WKT format. So, we need to let MySQL transform the WKT representation into its internal format.

This is where the convertToPHPValueSQL and convertToDatabaseValueSQL methods come into play.

This methods wrap a sql expression (the WKT representation of the Point) into MySQL functions PointFromText and AsText which convert WKT strings to and from the internal format of MySQL.

Note

When using DQL queries, the convertToPHPValueSQL and convertToDatabaseValueSQL methods only apply to identification variables and path expressions in SELECT clauses. Expressions in WHERE clauses are not wrapped!

If you want to use Point values in WHERE clauses, you have to implement a user defined function for PointFromText.

Example usage

<?php

// Bootstrapping stuff...
// $em = \Doctrine\ORM\EntityManager::create($connectionOptions, $config);

// Setup custom mapping type
use Doctrine\DBAL\Types\Type;

Type::addType('point', 'Geo\Types\Point');
$em->getConnection()->getDatabasePlatform()->registerDoctrineTypeMapping('point', 'point');

// Store a Location object
use Geo\Entity\Location;
use Geo\ValueObject\Point;

$location = new Location();

$location->setAddress('1600 Amphitheatre Parkway, Mountain View, CA');
$location->setPoint(new Point(37.4220761, -122.0845187));

$em->persist($location);
$em->flush();
$em->clear();

// Fetch the Location object
$query = $em->createQuery("SELECT l FROM Geo\Entity\Location WHERE l.address = '1600 Amphitheatre Parkway, Mountain View, CA'");
$location = $query->getSingleResult();

/* @var Geo\ValueObject\Point */
$point = $location->getPoint();



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