Symfony2: How to validate a form collection?

Question

symfony

There is the essence of contests and there is the essence of prizes. In the prizes there are fields "place" and "prize name".
Entities are connected by a one-to-many relationship.
The essence of competitions

/**
     * @ORM\OneToMany(targetEntity="Prize", mappedBy="contest", cascade={"persist"})
     *
     */
    protected $prizes;

Essence of prizes

/**
     * @ORM\ManyToOne(targetEntity="Contest", inversedBy="prizes")
     * @ORM\JoinColumn(name="contest_id", referencedColumnName="id")
     */
    protected $contest;

And there is a form in which to create a contest, in which you can add any number of prizes, but the "place" and "prize name" fields should not be empty.
In the essence of prizes, I added @Assert \NotBlank() annotations, but this did not help, when submitting the form, there is no message that the field cannot be empty, but an error appears saying that name=NULL cannot be saved in the database.
Then I found this article symfony.com/doc/current/reference/constraints/Coll... and added the following thing to the essence of the competition

/**
     * @ORM\OneToMany(targetEntity="Prize", mappedBy="contest", cascade={"persist"})
     * @Assert\Collection(
     *     fields = {
     *         "place" = @Assert\NotBlank(),
     *         "name" = @Assert\NotBlank(),
     *     },
     *     allowMissingFields = true
     * )
     *
     */
    protected $prizes;

In this case, in any scenario (whether the required fields are filled in or not), the message "This field was not expected" is displayed.
How to properly validate the fields I need?

Answer 1

symfony.com/doc/current/reference/constraints/Vali...

Answer 2

If you are using FormType then look this way stackoverflow.com/questions/10138505/symfony2-vali...