ModelManagerException: Failed to create object - symfony

Question

I'm using Sonata Admin bundle. When I submit a "Create entity" form the ModelManagerException is thrown if the form has some empty fields.
I've tracked this down to the PDOException that is thrown first. The exception is thrown because my empty fields get null values, but my table does not allow null values. I don't want to have null fields, I want empty string instead. How do I tell Sonata Admin class to create new entity with empty strings instead of nulls for fields without values?
This is the query that throws the exception:
INSERT INTO some_table (name, username, email) VALUES (?, ?, ?)' with params [null, "my name", "test#mailinator.com"]
These are the exceptions:
ModelManagerException: Failed to create object: Acme\DemoBundle\Entity\SomeEntity
SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'name' cannot be null
PDOException: SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'name' cannot be null
I tried setting $this->name = ''; explicitly in SomeEntity constructor but it didn't help. The query still had null instead of ''. I tried overriding getNewInstance() on my Admin class to set name to '' value, but it didn't help either - query still had null instead.
The weird thing is that I can have empty fields on entity edit form - the entity updates fine and empty fields are saved correctly to the database. Why is this happening?
Example code:
<?php
namespace Acme\DemoBundle\Entity
use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
/**
* #ORM\Entity
* #ORM\Table(name="some_table")
*/
class SomeEntity
{
/**
* #ORM\Column(type="integer")
* #ORM\Id
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #ORM\Column(type="string", length=255)
*
* We can't use Assert\NotNull()
* because Admin bundle uses null values for empty fields!
*/
protected $name;
// Other fields and methods.
}

Answer 1

you have two choices:
1- if you want the name field can be null, you need to edit the name annotation:
/**
* #ORM\Column(type="string", length=255, nullable=true)
*/
protected $name;
2- if you want the name field be just an empty string when you create new instance, you just have to add the prePersist in your entityAdmin:
public function prePersist($object)
{
$object->setName('');
}
I hope it helps :)

Answer 2

There is some DBAL exception associated with this. Scroll lower on the symfony exception page and you'll see it.