QCharts/CoreBundle/Form/Transformer/DirectoryTransformer.php
public function reverseTransform($value)
    {
        if (is_null($value))
        {
            return null;
        }

        $dir = $this->objectManager->getRepository('CoreBundle:Directory')
            ->find($value);
        if ($dir === null)
        {
            throw new TransformationFailedException("The directory was not found!");
        }
        return $dir;
    }
public function reverseTransform($value)
    {
        if (is_null($value))
        {
            return null;
        }

        $dir = $this->objectManager->getRepository('CoreBundle:Directory')
            ->find($value);
        if ($dir === null)
        {
            throw new TransformationFailedException("The directory was not found!");
        }
        return $dir;
    }
Transforms a value from the transformed representation to its original
representation.

This method is called when {@link Form::submit()} is called to transform the requests tainted data
into an acceptable format for your data processing/model layer.

This method must be able to deal with empty values. Usually this will
be an empty string, but depending on your implementation other empty
values are possible as well (such as empty strings). The reasoning behind
this is that value transformers must be chainable. If the
reverseTransform() method of the first value transformer outputs an
empty string, the second value transformer must be able to process that
value.

By convention, reverseTransform() should return NULL if an empty string
is passed.

@param mixed $value The value in the transformed representation

@return mixed The value in the original representation

@throws TransformationFailedException When the transformation fails.