validation.xml

<?xml version="1.0" encoding="UTF-8" ?>
<constraint-mapping xmlns="http://symfony.com/schema/dic/constraint-mapping"
                    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                    xsi:schemaLocation="http://symfony.com/schema/dic/constraint-mapping http://symfony.com/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd">

    <class name="SOTB\CoreBundle\Document\Torrent">
        <group-sequence-provider/>

        <property name="hash">
            <constraint name="MaxLength">
                <option name="limit">1024</option>
                <option name="groups">
                    <value>always</value>
                </option>
            </constraint>
            <constraint name="MinLength">
                <option name="limit">32</option>
                <option name="groups">
                    <value>hash</value>
                </option>
            </constraint>
        </property>
    </class>

</constraint-mapping>