Doctrine2 - how to do uniqueness validation?

Question

Doctrine ORM

The entity itself has a line

* @ORM\Table(name="certificates", uniqueConstraints={@ORM\UniqueConstraint(name="number", columns={"number"})})

those. doctrine knows that the number field has a unique parameter in the database
. How can I make sure that the doctrine checks whether the data is inserted into the database or not before writing the data to the database?