Datagrid filter for relationship object as text field (insted dropdown) in sonata admin in symfony 2.4

Question

I have an entity “Action” in relation to “User”. Created Admin CRUD controller in SonataAdminBundle. Everything works fine, except that the user filter appears as a drop-down list. I have 8k users and is growing, so you must understand why this is a problem.
I want the custom filter to be text entered and sent to search withLIKE %username%

Now I add user filter as follows: $datagridMapper->add('user').

I know that I can add a filter type and a field type, but I cannot find the correct combination and parameters. Found information about http://sonata-project.org/bundles/doctrine-orm-admin/master/doc/reference/filter_field_definition.html , but still failed.

Final decision

After Alex Togo answered, I used this code:

$datagridMapper->add('user', 'doctrine_orm_callback', array(
'callback' => function($queryBuilder, $alias, $field, $value) {
    if (empty($value['value'])) {
        return;
    }
    $queryBuilder->leftJoin(sprintf('%s.user', $alias), 'u');
    $queryBuilder->where('u.username LIKE :username');
    $queryBuilder->setParameter('username', '%'.$value['value'].'%');
    return true;
},
'field_type' => 'text'
))

Answer 1

- . , this. "field_type" "text" ( "" , ) querybuilder, .

Answer 2

doctrine_orm_choice.

protected function configureDatagridFilters(DatagridMapper $datagridMapper)
{
    $datagridMapper->add(
            'module',
            'doctrine_orm_choice',
            [],
            'choice',
            [
                'choices' => $this->filterModuleList
            ]
        )

        ....