Is there a way to enforce a unique column using doctrine2?

I'm assuming this is what you want?

<?php
/**
 * @Entity
 * @Table(name="ecommerce_products",uniqueConstraints={@UniqueConstraint(name="search_idx", columns={"name", "email"})})
 */
class ECommerceProduct
{
}

http://www.doctrine-project.org/docs/orm/2.0/en/reference/annotations-reference.html#annref-uniqueconstraint

Since I don't have your code I can't give you a practical example.

Just providing an alternate solution that is a little simpler.

If it is a single column, you could simply add a unique on the column definition:

class User
{
   /**
    * @Column(name="username", length=300, unique=true)
    */
   protected $username;
}

Documentation on this: https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/annotations-reference.html#annref_column

If you need a unique index on multiple columns, you still need to use the method Andreas provided.

note: I'm not sure since which version this is available. It might be this was not yet available in 2011.