Fix SoftDeletable Doctrine Entities with Unique Index Columns (Symfony2)

If you are using the Gedmo SoftDeletable Doctrine extension for entities that have some unique index columns, you will probably encounter a MySQL error when trying to add new entity with the same values as one previously deleted:

SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry ... for key …

Find out how to avoid this by reading this post: Symfony2: Gedmo SoftDeletable Doctrine Entities with Unique Index Columns.