As our Post Entity is composed of Value Objects like Body or PostId, it's a good idea to make Custom Mapping Types or use Doctrine Embeddables for them, as seen in the Value Objects chapter. This will make the object mapping considerably easier:

namespace InfrastructurePersistenceDoctrineTypes;

use DoctrineDBALTypesType;
use DoctrineDBALPlatformsAbstractPlatform;
use DomainModelBody;

class BodyType extends Type
{
    public function getSQLDeclaration(
        array $fieldDeclaration, AbstractPlatform $platform
    ) {
        return $platform->getVarcharTypeDeclarationSQL(
            $fieldDeclaration
        );
    }

    /**
     * @param string $value
     * @return Body
     */
    public function convertToPHPValue(
        $value, AbstractPlatform $platform
    ) {
        return new Body($value);
    }

    /**
     * @param Body $value
     */
    public function convertToDatabaseValue(
        $value, AbstractPlatform $platform
    ) {
        return $value->content();
    }

    public function getName()
    {
        return 'body';
    }
}

namespace InfrastructurePersistenceDoctrineTypes;

use DoctrineDBALTypesType;
use DoctrineDBALPlatformsAbstractPlatform;
use DomainModelPostId;

class PostIdType extends Type
{
    public function getSQLDeclaration(
        array $fieldDeclaration, AbstractPlatform $platform
    ) {
        return $platform->getGuidTypeDeclarationSQL(
            $fieldDeclaration
        );
    }

    /**
     * @param string $value
     * @return PostId
     */
    public function convertToPHPValue(
        $value, AbstractPlatform $platform
    ) {
        return new PostId($value);
    }

    /**
     * @param PostId $value
     */
    public function convertToDatabaseValue(
        $value, AbstractPlatform $platform
    ) {
       return $value->id();
    }

    public function getName()
    { 
       return 'post_id';
    }
}

Don't forget to implement the __toString magic method on the PostId Value Object, as Doctrine requires this:

class PostId 
{ 
    // ...   
    public function __toString()
    {
        return $this->id;
    }
}

Doctrine offers multiple formats for the mapping, such as YAML, XML, or annotations. XML is our preferred choice, as it provides robust IDE autocompletion:

<?xml version="1.0" encoding="UTF-8"?>
<doctrine-mapping
    xmlns="http://doctrine-project.org/schemas/orm/doctrine-mapping"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://doctrine-project.org/schemas/orm/doctrine-mapping
    http://raw.github.com/doctrine/doctrine2/master/doctrine-mapping.xsd">

    <entity name="DomainModelPost" table="posts">
        <id name="id" type="post_id" column="id">
            <generator strategy="NONE" />
        </id>
        <field name="body" type="body" length="250" column="body"/>
        <field name="createdAt" type="datetime" column="created_at"/>
    </entity>

</doctrine-mapping>